Intial commit - import scenario 2

22 files changed, 3096 insertions, 0 deletions

diff --git a/src/pl/edu/mimuw/cloudatlas/model/Attribute.java b/src/pl/edu/mimuw/cloudatlas/model/Attribute.java
new file mode 100644
index 0000000..d0af5bb
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/Attribute.java
@@ -0,0 +1,107 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+/**
+ * Represents an attribute (without value, name only).
+ * <p>
+ * A valid attribute name is an identifier starting with a letter and containing only letters and digits. It can
+ * additionally start with an ampersand - such names are reserved for queries.
+ * <p>
+ * This class is immutable.
+ */
+public class Attribute {
+	private final String name;
+	
+	/**
+	 * Creates a new <code>Attribute</code> object with the specified <code>name</code>.
+	 * 
+	 * @param name the name of the attribute
+	 * @throws IllegalArgumentException if the <code>name</code> does not meet the rules
+	 */
+	public Attribute(String name) {
+		if(!name.matches("^&?[a-zA-Z]{1}[a-zA-z0-9_]*$"))
+			throw new IllegalArgumentException("Invalid name: may contain only letters, digits, underscores, "
+					+ "must start with a letter and may optionally have an ampersand at the beginning.");
+		this.name = name;
+	}
+	
+	/**
+	 * Indicates whether an <code>attribute</code> represents a query. This is true if and only if attribute name starts with an
+	 * ampersand.
+	 * 
+	 * @param attribute the attribute to check
+	 * @return whether the <code>attribute</code> represents a query
+	 */
+	public static boolean isQuery(Attribute attribute) {
+		return attribute.getName().startsWith("&");
+	}
+	
+	/**
+	 * Gets the name of this attribute.
+	 * 
+	 * @return string representing name
+	 */
+	public String getName() {
+		return name;
+	}
+	
+	/**
+	 * Returns a hash code value for this attribute. For a proper behavior when using <code>Attribute</code> objects in
+	 * <code>HashMap</code>, <code>HashSet</code> etc. this is the hash code of a string representing attribute name.
+	 * 
+	 * @return hash code for this attribute
+	 */
+	@Override
+	public int hashCode() {
+		return name.hashCode();
+	}
+	
+	/**
+	 * Indicates whether another object is equal to this attribute.
+	 * 
+	 * @param object the object to check
+	 * @return true if and only if the <code>object</code> is an instance of <code>Attribute</code> class and has
+	 * identical name
+	 */
+	@Override
+	public boolean equals(Object object) {
+		if(object == null)
+			return false;
+		if(getClass() != object.getClass())
+			return false;
+		return name.equals(((Attribute)object).name);
+	}
+	
+	/**
+	 * Returns a textual representation of this attribute.
+	 * 
+	 * @return the name of this attribute
+	 */
+	@Override
+	public String toString() {
+		return name;
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/AttributesMap.java b/src/pl/edu/mimuw/cloudatlas/model/AttributesMap.java
new file mode 100644
index 0000000..86f8969
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/AttributesMap.java
@@ -0,0 +1,282 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.Map.Entry;
+
+/**
+ * Represents a map from <code>Attribute</code> to <code>Value</code>. It cannot contain duplicate keys.
+ */
+public class AttributesMap implements Iterable<Entry<Attribute, Value>>, Cloneable {
+	private Map<Attribute, Value> map = new HashMap<Attribute, Value>();
+	
+	private void checkNulls(Attribute attribute, Value value) {
+		if(attribute == null)
+			throw new NullPointerException("The attribute cannot be null.");
+		if(value == null)
+			throw new NullPointerException(
+					"The value cannot be null. You may want create a Value object that contains null.");
+	}
+	
+	/**
+	 * Adds to this map a new <code>attribute</code> mapping to the specified <code>value</code>. The
+	 * <code>attribute</code> cannot already exist in the map. To overwrite an existing attribute, use method
+	 * {@link #addOrChange(Attribute, Value)} instead.
+	 * 
+	 * @param attribute the attribute to add
+	 * @param value the value for the <code>attribute</code>
+	 * @throws IllegalArgumentException if the <code>attribute</code> already exists in this map
+	 * @throws NullPointerException if either the <code>attribute</code> or the <code>value</code> is <code>null</code>;
+	 * for null value, create a <code>Value</code> object containing <code>null</code>
+	 * @see #addOrChange(Attribute, Value)
+	 * @see #add(String, Value)
+	 * @see #add(Entry)
+	 * @see #add(AttributesMap)
+	 */
+	public void add(Attribute attribute, Value value) {
+		if(getOrNull(attribute) != null)
+			throw new IllegalArgumentException("Attribute \"" + attribute.getName()
+					+ "\" already exists. Use method addOrChange(Attribute, Value) instead.");
+		checkNulls(attribute, value);
+		map.put(attribute, value);
+	}
+	
+	/**
+	 * Adds a new attribute mapping to the specified <code>value</code>. Convenient version of
+	 * {@link #add(Attribute, Value)}.
+	 * 
+	 * @param name the attribute name
+	 * @param value the attribute value
+	 * @see #add(Attribute, Value)
+	 * @see #addOrChange(String, Value)
+	 */
+	public void add(String name, Value value) {
+		add(new Attribute(name), value);
+	}
+	
+	/**
+	 * Adds a new mapping to this map. Convenient version of {@link #add(Attribute, Value)}.
+	 * 
+	 * @param entry a pair containing both an attribute and a value
+	 * @see #add(Attribute, Value)
+	 * @see #addOrChange(Entry)
+	 */
+	public void add(Entry<Attribute, Value> entry) {
+		add(entry.getKey(), entry.getValue());
+	}
+	
+	/**
+	 * Adds all entries from another map to this map. This method uses {@link #add(Attribute, Value)}, so it throws an
+	 * exception when trying to overwrite an existing attribute.
+	 * 
+	 * @param attributes the map to add
+	 * @see #add(Attribute, Value)
+	 * @see #addOrChange(AttributesMap)
+	 */
+	public void add(AttributesMap attributes) {
+		for(Entry<Attribute, Value> entry : attributes.map.entrySet())
+			add(entry);
+	}
+	
+	/**
+	 * Adds to this map a new <code>attribute</code> mapping to the specified <code>value</code>. Unlike
+	 * {@link #add(Attribute, Value)}, this method overwrites an existing attribute with the same name.
+	 * 
+	 * @param attribute the attribute to add or overwrite
+	 * @param value the value for the <code>attribute</code>
+	 * @throws NullPointerException if either the <code>attribute</code> or the <code>value</code> is <code>null</code>;
+	 * for null value create a <code>Value</code> object containing <code>null</code>
+	 * @see #add(Attribute, Value)
+	 * @see #addOrChange(String, Value)
+	 * @see #addOrChange(Entry)
+	 * @see #addOrChange(AttributesMap)
+	 */
+	public void addOrChange(Attribute attribute, Value value) {
+		map.put(attribute, value);
+		checkNulls(attribute, value);
+	}
+	
+	/**
+	 * Adds a new attribute< mapping to the specified <code>value</code> or overwrites an existing one. Convenient
+	 * version of {@link #addOrChange(Attribute, Value)}.
+	 * 
+	 * @param name the attribute name
+	 * @param value the attribute value
+	 * @see #addOrChange(Attribute, Value)
+	 * @see #add(String, Value)
+	 */
+	public void addOrChange(String name, Value value) {
+		addOrChange(new Attribute(name), value);
+	}
+	
+	/**
+	 * Adds a new mapping to this map or overwrites an existing one with the same attribute name. Convenient version of
+	 * {@link #addOrChange(Attribute, Value)}.
+	 * 
+	 * @param entry a pair containing both an attribute and a value
+	 * @see #addOrChange(Attribute, Value)
+	 * @see #add(Entry)
+	 */
+	public void addOrChange(Entry<Attribute, Value> entry) {
+		addOrChange(entry.getKey(), entry.getValue());
+	}
+	
+	/**
+	 * Adds all entries from another map to this map. If any attribute with the same name exists in this map, it will be
+	 * overwritten.
+	 * 
+	 * @param attributes the map to add
+	 * @see #addOrChange(Attribute, Value)
+	 * @see #add(AttributesMap)
+	 */
+	public void addOrChange(AttributesMap attributes) {
+		for(Entry<Attribute, Value> entry : attributes.map.entrySet())
+			addOrChange(entry);
+	}
+	
+	private void checkAttribute(Attribute attribute) {
+		if(attribute == null)
+			throw new NullPointerException("The attribute cannot be null.");
+	}
+	
+	/**
+	 * Gets the value mapped to the specified <code>attribute</code>. If such mapping does not exist, this method throws
+	 * an exception. If this is not an expected behavior, use method {@link #getOrNull(Attribute)} instead.
+	 * 
+	 * @param attribute the attribute to obtain
+	 * @return the value mapped to the <code>attribute</code>
+	 * @throws IllegalArgumentException if no value is mapped to the <code>attribute</code>
+	 * @throws NullPointerException if the <code>attribute</code> is <code>null</code>
+	 * @see #getOrNull(Attribute)
+	 * @see #get(String)
+	 */
+	public Value get(Attribute attribute) {
+		Value value = getOrNull(attribute);
+		if(value == null)
+			throw new IllegalArgumentException("Attribute " + attribute.getName()
+					+ " does not exist. Use method getOrNull(Attribute) instead.");
+		return value;
+	}
+	
+	/**
+	 * Gets the value mapped to the specified attribute. Convenient version of {@link #get(Attribute)}.
+	 * 
+	 * @param name name of the attribute
+	 * @return the value mapped to the specified attribute
+	 * @see #get(Attribute)
+	 * @see #getOrNull(String)
+	 */
+	public Value get(String name) {
+		return get(new Attribute(name));
+	}
+	
+	/**
+	 * Gets the value mapped to the specified <code>attribute</code>. Unlike {@link #get(Attribute)}, this method
+	 * returns <code>null</code> if the requested mapping does not exist.
+	 * 
+	 * @param attribute the attribute to obtain
+	 * @return the value mapped to the <code>attribute</code> or <code>null</code> if it does not exist
+	 * @throws NullPointerException if the <code>attribute</code> is <code>null</code>
+	 * @see #get(Attribute)
+	 * @see #getOrNull(String)
+	 */
+	public Value getOrNull(Attribute attribute) {
+		checkAttribute(attribute);
+		return map.get(attribute);
+	}
+	
+	/**
+	 * Gets the value mapped to the specified attribute. Convenient version of {@link #getOrNull(Attribute)}.
+	 * 
+	 * @param name name of the attribute
+	 * @return the value mapped to specified attribute or <code>null</code> if it does not exist
+	 * @see #getOrNull(Attribute)
+	 * @see #getOr(String)
+	 */
+	public Value getOrNull(String name) {
+		return getOrNull(new Attribute(name));
+	}
+	
+	/**
+	 * Removes the specified <code>attribute</code> and its value from this map. If the <code>attribute</code> does not
+	 * exist, this method performs nothing.
+	 * 
+	 * @param attribute the attribute to remove
+	 * @throws NullPointerException if the <code>attribute</code> is <code>null</code>
+	 * @see #remove(String)
+	 */
+	public void remove(Attribute attribute) {
+		checkAttribute(attribute);
+		map.remove(attribute);
+	}
+	
+	/**
+	 * Removes the specified attribute and its value from this map. Convenient version of {@link #remove(Attribute)}.
+	 * 
+	 * @param name the name of the attribute to remove
+	 * @see #remove(Attribute)
+	 */
+	public void remove(String name) {
+		map.remove(new Attribute(name));
+	}
+	
+	/**
+	 * Returns an iterator over all entries stored in this map.
+	 * 
+	 * @return an iterator for this map
+	 * @see java.util.Iterator
+	 * @see java.lang.Iterable
+	 */
+	@Override
+	public Iterator<Entry<Attribute, Value>> iterator() {
+		return map.entrySet().iterator();
+	}
+	
+	/**
+	 * Creates a copy of this map. Since <code>Value</code> and <code>Attribute</code> are immutable classes, this
+	 * method does not clone them.
+	 * 
+	 * @return a copy of this map containing identical entries
+	 */
+	@Override
+	public AttributesMap clone() {
+		AttributesMap result = new AttributesMap();
+		result.add(this);
+		return result;
+	}
+	
+	/**
+	 * Returns a string representation of this map listing all key-value pairs stored in it.
+	 * 
+	 * @return a string representation of this object
+	 */
+	@Override
+	public String toString() {
+		return map.toString();
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/IncompatibleTypesException.java b/src/pl/edu/mimuw/cloudatlas/model/IncompatibleTypesException.java
new file mode 100644
index 0000000..e8a962d
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/IncompatibleTypesException.java
@@ -0,0 +1,81 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import pl.edu.mimuw.cloudatlas.model.Value.Operation;
+
+/**
+ * An exception thrown when an unsupported binary operation on values is requested.
+ * 
+ * @see UnsupportedValueOperationException
+ * @see UnsupportedConversionException
+ */
+@SuppressWarnings("serial")
+public class IncompatibleTypesException extends UnsupportedOperationException {
+	private final Type left;
+	private final Type right;
+	private final Operation operation;
+	
+	/**
+	 * Creates a new object representing this exception.
+	 * 
+	 * @param left type of a left operand
+	 * @param right type of a right operand
+	 * @param operation an operation that caused this exception
+	 */
+	protected IncompatibleTypesException(Type left, Type right, Operation operation) {
+		super("Incompatible types: " + left + " and " + right + " in operation " + operation + ".");
+		this.left = left;
+		this.right = right;
+		this.operation = operation;
+	}
+	
+	/**
+	 * Gets a type of a left operand in an operation that caused this exception.
+	 * 
+	 * @return the type of the left operand
+	 */
+	public Type getLeft() {
+		return left;
+	}
+	
+	/**
+	 * Gets a type of a right operand in an operation that caused this exception.
+	 * 
+	 * @return the type of the right operand
+	 */
+	public Type getRight() {
+		return right;
+	}
+	
+	/**
+	 * Gets an object representing an operation that caused this exception.
+	 * 
+	 * @return an operation that caused this exception
+	 */
+	public Operation getOperation() {
+		return operation;
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/PathName.java b/src/pl/edu/mimuw/cloudatlas/model/PathName.java
new file mode 100644
index 0000000..c5ef4e8
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/PathName.java
@@ -0,0 +1,180 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Represent a fully qualified name of a zone, also known as a global name or a path name. This class is immutable.
+ */
+public class PathName {
+	/**
+	 * The object representing a name of the root zone (/).
+	 */
+	public static final PathName ROOT = new PathName("/");
+	
+	private final List<String> components;
+	private final String name;
+	
+	/**
+	 * Creates a <code>PathName</code> object representing the specified path. For the root zone, there are three
+	 * accepted forms: <code>null</code> reference, empty string or slash. Any other zone is represented by a string
+	 * starting with slash and containing names of zones at each level of hierarchy, separated by slashes. Zone name
+	 * must contain only letters and digits.
+	 * 
+	 * @param name path name of a zone, for instance: <code>/warsaw/uw/violet07</code>
+	 * @throws IllegalArgumentException if the <code>name</code> is incorrect
+	 */
+	public PathName(String name) {
+		// we accept null and "/" as names of a root zone, however, we convert all of them to ""
+		name = name == null || name.equals("/")? "" : name.trim();
+		if(!name.matches("(/\\w+)*"))
+			throw new IllegalArgumentException("Incorrect fully qualified name: " + name + ".");
+		this.name = name;
+		components = name.equals("")? new ArrayList<String>() : Arrays.asList(name.substring(1).split("/"));
+	}
+	
+	/**
+	 * Creates a <code>PathName</code> object from a collection of zones names. Every zone name must contain only
+	 * letters and digits.
+	 * 
+	 * @param components a collection of zones names at subsequent levels of hierarchy (starting from root); empty
+	 * collection represents the root zone
+	 * @throws IllegalArgumentException if any zone name is incorrect
+	 */
+	public PathName(Collection<String> components) {
+		this.components = new ArrayList<String>(components);
+		if(components.isEmpty())
+			this.name = "";
+		else {
+			String currentName = "";
+			for(String c : components) {
+				currentName += "/" + c;
+				if(!c.matches("\\w+"))
+					throw new IllegalArgumentException("Incorrect component " + c + ".");
+			}
+			this.name = currentName;
+		}
+	}
+	
+	/**
+	 * Gets zones names at subsequent levels of hierarchy, starting from root. For the root zone, this method returns an
+	 * empty collection. Modifying returned list will throw an exception.
+	 * 
+	 * @return a collection of zones names
+	 */
+	public List<String> getComponents() {
+		return Collections.unmodifiableList(components);
+	}
+	
+	/**
+	 * Gets a full path name. For the root zone, this method returns an empty string.
+	 * 
+	 * @return a path name represented by this object
+	 * @see #toString()
+	 */
+	public String getName() {
+		return name;
+	}
+	
+	/**
+	 * Gets a name one level up in a hierarchy. For the root zone, this method returns a new instance of the same zone.
+	 * 
+	 * @return a new <code>PathName</code> object representing a zone one level up in the hierarchy
+	 */
+	public PathName levelUp() {
+		List<String> componentsUp = new ArrayList<String>(components);
+		if(!componentsUp.isEmpty())
+			componentsUp.remove(componentsUp.size() - 1);
+		return new PathName(componentsUp);
+	}
+	
+	/**
+	 * Gets a name one level down in a hierarchy.
+	 * 
+	 * @param son zone name at a lower level
+	 * @return a new <code>PathName</code> object representing a zone one level down in the hierarchy
+	 */
+	public PathName levelDown(String son) {
+		return new PathName(name + "/" + son);
+	}
+	
+	/**
+	 * Gets a zone name at the lowest level (highest number) in a hierarchy.
+	 * 
+	 * @return a leaf zone
+	 * @throws UnsupportedOperationException if this object represents the root zone
+	 */
+	public String getSingletonName() {
+		try {
+			return components.get(components.size() - 1);
+		} catch(IndexOutOfBoundsException exception) {
+			throw new UnsupportedOperationException("getSingletonName() is not supported for the root zone.");
+		}
+	}
+	
+	/**
+	 * Returns a hash code value for this object. This method returns a hash code of a string representing full path
+	 * name.
+	 * 
+	 * @return a hash code for this object
+	 */
+	@Override
+	public int hashCode() {
+		return name.hashCode();
+	}
+	
+	/**
+	 * Indicates whether this object is equal to another. A <code>PathName</code> object is equal to other objects of
+	 * the same class representing identical path name.
+	 * 
+	 * @object the object to check
+	 * @return whether the <code>object</code> is equal to this name
+	 */
+	@Override
+	public boolean equals(Object object) {
+		if(object == null)
+			return false;
+		if(getClass() != object.getClass())
+			return false;
+		return name.equals(((PathName)object).name);
+	}
+	
+	/**
+	 * Returns a textual representation for this <code>PathName</code>. For the root zone, unlike {@link #getName()},
+	 * this method returns slash.
+	 * 
+	 * @return a path name for this object
+	 * @see #getName()
+	 */
+	@Override
+	public String toString() {
+		return name.equals("")? "/" : getName();
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/Type.java b/src/pl/edu/mimuw/cloudatlas/model/Type.java
new file mode 100644
index 0000000..ba6cf62
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/Type.java
@@ -0,0 +1,81 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+/**
+ * A type of a value that may be stored as an attribute.
+ */
+public abstract class Type {
+	/**
+	 * A primary type. This is a characteristic that every type has. It can be extended: for instance a collection may
+	 * be parameterized with a type of stored values.
+	 */
+	public static enum PrimaryType {
+		BOOLEAN, CONTACT, DOUBLE, DURATION, INT, LIST, NULL, SET, STRING, TIME,
+	}
+	
+	private final PrimaryType primaryType;
+	
+	/**
+	 * Creates a <code>Type</code> object with a given primary type.
+	 * 
+	 * @param primaryType a primary type for this type
+	 */
+	public Type(PrimaryType primaryType) {
+		this.primaryType = primaryType;
+	}
+	
+	/**
+	 * Returns a primary type of this type.
+	 * 
+	 * @return a primary type
+	 */
+	public PrimaryType getPrimaryType() {
+		return primaryType;
+	}
+	
+	/**
+	 * Indicates whether this type can be implicitly "cast" to given one and vice verse. This is introduced to deal with
+	 * null values. In practice, two types are compatible either if they are the same or if one them is a special
+	 * "null type".
+	 * 
+	 * @param type a type to check
+	 * @return whether two types are compatible with each other
+	 * @see TypePrimitive#NULL
+	 * @see ValueNull
+	 */
+	public boolean isCompatible(Type type) {
+		return getPrimaryType() == PrimaryType.NULL || type.getPrimaryType() == PrimaryType.NULL;
+	}
+	
+	/**
+	 * Indicates whether this type represents a collection.
+	 * 
+	 * @return true for collections, false otherwise
+	 */
+	public boolean isCollection() {
+		return false;
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/TypeCollection.java b/src/pl/edu/mimuw/cloudatlas/model/TypeCollection.java
new file mode 100644
index 0000000..9ace5c5
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/TypeCollection.java
@@ -0,0 +1,116 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import java.util.Collection;
+
+import pl.edu.mimuw.cloudatlas.model.Type;
+import pl.edu.mimuw.cloudatlas.model.TypePrimitive;
+import pl.edu.mimuw.cloudatlas.model.Value;
+import pl.edu.mimuw.cloudatlas.model.ValueNull;
+
+/**
+ * Represents a collection type with specified element type.
+ * 
+ * @see TypePrimitve
+ */
+public class TypeCollection extends Type {
+	private final Type elementType;
+	
+	/**
+	 * Creates a new collection type.
+	 * 
+	 * @param primaryType a type of this collection (set, list etc.)
+	 * @param elementType a type of an element of this collection; may be a complex type (for instance
+	 * <code>TypeCollection</code>)
+	 */
+	public TypeCollection(PrimaryType primaryType, Type elementType) {
+		super(primaryType);
+		switch(primaryType) {
+			case LIST:
+			case SET:
+				break;
+			default:
+				throw new IllegalArgumentException("This class can represent a collection only (list, set etc.).");
+		}
+		this.elementType = elementType;
+	}
+	
+	/**
+	 * Gets a type of elements stored in this collection.
+	 * 
+	 * @return type of element in this collection
+	 */
+	public Type getElementType() {
+		return elementType;
+	}
+	
+	/**
+	 * Returns a friendly textual representation of this collection, for instance: "SET of (STRING)".
+	 * 
+	 * @return a textual representation of this type
+	 */
+	@Override
+	public String toString() {
+		return getPrimaryType().toString() + " of (" + elementType.toString() + ")";
+	}
+	
+	@Override
+	public boolean isCompatible(Type type) {
+		return super.isCompatible(type)
+				|| (getPrimaryType() == type.getPrimaryType() && elementType
+						.isCompatible(((TypeCollection)type).elementType));
+	}
+	
+	@Override
+	public boolean isCollection() {
+		return true;
+	}
+	
+	/**
+	 * Returns a type of all elements in the specified collection. If the collection is empty, this method returns
+	 * {@link TypePrimitive#NULL}. If the collection contains at least two elements of distinct types that are not nulls,
+	 * an exception is thrown.
+	 * 
+	 * @param collection a collection of values to check
+	 * @return type of elements in this collection
+	 * @throws IllegalArgumentException if the collection contains non-null elements of different types
+	 */
+	public static Type computeElementType(Collection<Value> collection) {
+		Type mainType = null;
+		
+		for(Value v : collection) {
+			if(v.isNull())
+				v = ValueNull.getInstance();
+			if(mainType == null) {
+				if(v.getType().getPrimaryType() != Type.PrimaryType.NULL)
+					mainType = v.getType();
+			} else if(!mainType.isCompatible(v.getType()))
+				throw new IllegalArgumentException("Collection has non-null elements of different types.");
+		}
+		
+		return mainType == null? TypePrimitive.NULL : mainType;
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/TypePrimitive.java b/src/pl/edu/mimuw/cloudatlas/model/TypePrimitive.java
new file mode 100644
index 0000000..4940a16
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/TypePrimitive.java
@@ -0,0 +1,108 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+/**
+ * Convenient class for types that just wrap ordinary Java types.
+ * 
+ * @see TypeCollection
+ */
+public class TypePrimitive extends Type {
+	/**
+	 * Boolean type.
+	 */
+	public static final TypePrimitive BOOLEAN = new TypePrimitive(PrimaryType.BOOLEAN);
+	
+	/**
+	 * Contact type.
+	 */
+	public static final TypePrimitive CONTACT = new TypePrimitive(PrimaryType.CONTACT);
+	
+	/**
+	 * Double type.
+	 */
+	public static final TypePrimitive DOUBLE = new TypePrimitive(PrimaryType.DOUBLE);
+	
+	/**
+	 * Duration type.
+	 */
+	public static final TypePrimitive DURATION = new TypePrimitive(PrimaryType.DURATION);
+	
+	/**
+	 * Integer type.
+	 */
+	public static final TypePrimitive INTEGER = new TypePrimitive(PrimaryType.INT);
+	
+	/**
+	 * A special "null type" that represents null value of an unknown type. It can be converted to any other type.
+	 * 
+	 * @see Type#isCompatible(Type)
+	 * @see ValueNull
+	 */
+	public static final TypePrimitive NULL = new TypePrimitive(PrimaryType.NULL);
+	
+	/**
+	 * String type.
+	 */
+	public static final TypePrimitive STRING = new TypePrimitive(PrimaryType.STRING);
+	
+	/**
+	 * Time type.
+	 */
+	public static final TypePrimitive TIME = new TypePrimitive(PrimaryType.TIME);
+	
+	private TypePrimitive(PrimaryType primaryType) {
+		super(primaryType);
+		switch(primaryType) {
+			case BOOLEAN:
+			case CONTACT:
+			case DOUBLE:
+			case DURATION:
+			case INT:
+			case NULL:
+			case STRING:
+			case TIME:
+				break;
+			default:
+				throw new IllegalArgumentException(
+						"This class can represent a primitive type only (boolean, int etc.).");
+		}
+	}
+	
+	/**
+	 * Gets a textual representation of this type.
+	 * 
+	 * @return a string representing this type
+	 */
+	@Override
+	public String toString() {
+		return getPrimaryType().toString();
+	}
+	
+	@Override
+	public boolean isCompatible(Type type) {
+		return super.isCompatible(type) || getPrimaryType() == type.getPrimaryType();
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/UnsupportedConversionException.java b/src/pl/edu/mimuw/cloudatlas/model/UnsupportedConversionException.java
new file mode 100644
index 0000000..024c89f
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/UnsupportedConversionException.java
@@ -0,0 +1,67 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+/**
+ * An exception describing unsupported conversion of a value to another type.
+ * 
+ * @see IncompatibleTypesException
+ * @see UnsupportedValueOperationException
+ */
+@SuppressWarnings("serial")
+public class UnsupportedConversionException extends UnsupportedOperationException {
+	private final Type from;
+	private final Type to;
+	
+	/**
+	 * Creates a new instance of this this exception.
+	 * 
+	 * @param from source type of an unsupported conversion
+	 * @param to destination type of an unsupported conversion
+	 */
+	protected UnsupportedConversionException(Type from, Type to) {
+		super("Type " + from + " cannot be converted to " + to + ".");
+		this.from = from;
+		this.to = to;
+	}
+	
+	/**
+	 * Gets a source type of an unsupported conversion that caused this exception.
+	 * 
+	 * @return source type
+	 */
+	public Type getFrom() {
+		return from;
+	}
+	
+	/**
+	 * Gets a destination type of an unsupported conversion that caused this exception.
+	 * 
+	 * @return destination type
+	 */
+	public Type getTo() {
+		return to;
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/UnsupportedValueOperationException.java b/src/pl/edu/mimuw/cloudatlas/model/UnsupportedValueOperationException.java
new file mode 100644
index 0000000..e292265
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/UnsupportedValueOperationException.java
@@ -0,0 +1,69 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import pl.edu.mimuw.cloudatlas.model.Value.Operation;
+
+/**
+ * An exception caused by calling an unsupported unary operation on value.
+ * 
+ * @see IncompatibleTypesException
+ * @see UnsupportedConversionException
+ */
+@SuppressWarnings("serial")
+public class UnsupportedValueOperationException extends UnsupportedOperationException {
+	private final Type left;
+	private final Operation operation;
+	
+	/**
+	 * Creates a new object representing this exception.
+	 * 
+	 * @param left type of a value that was an argument of an operation that caused this exception
+	 * @param operation the operation that caused this exception
+	 */
+	protected UnsupportedValueOperationException(Type left, Operation operation) {
+		super("Type: " + left + " does not provide operation " + operation + ".");
+		this.left = left;
+		this.operation = operation;
+	}
+	
+	/**
+	 * Gets a type of value that was an argument to an operation that caused this exception.
+	 * 
+	 * @return first argument of the operation
+	 */
+	public Type getLeft() {
+		return left;
+	}
+	
+	/**
+	 * Gets an operation that caused this exception.
+	 * 
+	 * @return the operation
+	 */
+	public Operation getOperation() {
+		return operation;
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/Value.java b/src/pl/edu/mimuw/cloudatlas/model/Value.java
new file mode 100644
index 0000000..ad1887d
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/Value.java
@@ -0,0 +1,241 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import pl.edu.mimuw.cloudatlas.model.Value;
+
+/**
+ * A single value stored as an attribute.
+ */
+public abstract class Value {
+	/**
+	 * An operation that may be performed on values.
+	 */
+	public enum Operation {
+		EQUAL, COMPARE, ADD, SUBTRACT, MULTIPLY, DIVIDE, MODULO, AND, OR, REG_EXPR, NEGATE, VALUE_SIZE,
+	}
+	
+	/**
+	 * Gets type of this value.
+	 * 
+	 * @return type of this value
+	 */
+	public abstract Type getType();
+	
+	/**
+	 * Indicates whether this value is null. Distinct from a <code>Value</code> reference that is <code>null</code>
+	 * itself.
+	 * 
+	 * @return true if and only if this value is null
+	 */
+	public abstract boolean isNull();
+	
+	protected final void sameTypesOrThrow(Value value, Operation operation) {
+		if(!getType().isCompatible(value.getType()))
+			throw new IncompatibleTypesException(getType(), value.getType(), operation);
+	}
+	
+	/**
+	 * Checks whether this value is equal to the specified one (operator ==).
+	 * 
+	 * @param value the right side of the operator
+	 * @return a <code>ValueBoolean</code> representing true if and only if both values are equal
+	 * @throws UnsupportedValueOperationException if this operation is unsupported for these values
+	 */
+	public Value isEqual(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.EQUAL);
+	}
+	
+	/**
+	 * Indicates whether this object is equal to another one.
+	 * 
+	 * @param object the object to check
+	 * @return whether two objects are equal
+	 */
+	@Override
+	public boolean equals(Object object) {
+		if(!(object instanceof Value))
+			return false;
+		return ((ValueBoolean)isEqual((Value)object)).getValue();
+	}
+	
+	/**
+	 * Checks whether this value is lower than the specified one (operator <=).
+	 * 
+	 * @param value the right side of the operator
+	 * @return a <code>ValueBoolean</code> representing true if and only if this value is lower than the provided one
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value isLowerThan(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.COMPARE);
+	}
+	
+	/**
+	 * Returns a new value created by adding argument to this value (operator +).
+	 * 
+	 * @param the right side of the operator
+	 * @return a sum of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value addValue(Value value) {
+		// name clash with add from List interface
+		throw new UnsupportedValueOperationException(getType(), Operation.ADD);
+	}
+	
+	/**
+	 * Returns a new value created by subtracting argument from this value (operator -).
+	 * 
+	 * @param the right side of the operator
+	 * @return a difference of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value subtract(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.SUBTRACT);
+	}
+	
+	/**
+	 * Returns a new value created by multiplying this value by an argument (operator *).
+	 * 
+	 * @param the right side of the operator
+	 * @return a product of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value multiply(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.MULTIPLY);
+	}
+	
+	/**
+	 * Returns a new value created by dividing this value by an argument (operator /).
+	 * 
+	 * @param the right side of the operator
+	 * @return a quotient of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value divide(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.DIVIDE);
+	}
+	
+	/**
+	 * Returns a remainder of a division of this value by an argument (operator %).
+	 * 
+	 * @param the right side of the operator
+	 * @return a remainder
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * incompatible or non-numeric types)
+	 */
+	public Value modulo(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.MODULO);
+	}
+	
+	/**
+	 * Returns a result of a logical and (operator &&).
+	 * 
+	 * @param value the right side of the operator
+	 * @return a conjunction of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * non-boolean types)
+	 */
+	public Value and(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.AND);
+	}
+	
+	/**
+	 * Returns a result of a logical or (operator ||).
+	 * 
+	 * @param value the right side of the operator
+	 * @return an alternative of two values
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values (for example
+	 * non-boolean types)
+	 */
+	public Value or(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.OR);
+	}
+	
+	/**
+	 * Returns a result of applying to this value a regular expression specified as an argument..
+	 * 
+	 * @param value the regular expression
+	 * @return a <code>ValueBoolean</code> representing true if and only if this value matches provided regular
+	 * expression
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for these values
+	 */
+	public Value regExpr(Value value) {
+		throw new UnsupportedValueOperationException(getType(), Operation.REG_EXPR);
+	}
+	
+	/**
+	 * Returns a negation (numeric or logical) of this value. This may refer to operator - or !, depending on type.
+	 * 
+	 * @return a value that is negation of this value
+	 * @throws UnsupportedValueOperationException if this operator is unsupported for this value
+	 */
+	public Value negate() { // !, -
+		throw new UnsupportedValueOperationException(getType(), Operation.NEGATE);
+	}
+	
+	/**
+	 * Returns a size of this value. Semantic depends on type.
+	 * 
+	 * @return a size of this value
+	 * @throws UnsupportedValueOperationException if this operation is unsupported for this value
+	 */
+	public Value valueSize() {
+		// name clash with size from List interface
+		throw new UnsupportedValueOperationException(getType(), Operation.VALUE_SIZE);
+	}
+	
+	/**
+	 * Returns this value converted to another type.
+	 * 
+	 * @param to a desired type
+	 * @return this value converted to the <code>type</code>
+	 * @throws UnsupportedConversionException if a requested conversion is unsupported
+	 */
+	public abstract Value convertTo(Type to);
+	
+	/**
+	 * Returns a textual representation of this value. This method uses conversion to <code>ValueString</code>.
+	 * 
+	 * @return a textual representation of this value
+	 * @see #convertTo(Type)
+	 */
+	@Override
+	public String toString() {
+		return ((ValueString)convertTo(TypePrimitive.STRING)).getValue();
+	}
+	
+	/**
+	 * Returns a default value (such as uninitialized variable). This may be <code>0</code> for integer types,
+	 * <code>false</code> for boolean, <code>null</code> for complex types etc.
+	 * 
+	 * @return a default value of this type
+	 */
+	public abstract Value getDefaultValue();
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueBoolean.java b/src/pl/edu/mimuw/cloudatlas/model/ValueBoolean.java
new file mode 100644
index 0000000..1ca20fc
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueBoolean.java
@@ -0,0 +1,93 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import pl.edu.mimuw.cloudatlas.model.Value;
+import pl.edu.mimuw.cloudatlas.model.ValueBoolean;
+
+/**
+ * A class that wraps a Java <code>Boolean</code> object.
+ */
+public class ValueBoolean extends ValueSimple<Boolean> {
+	/**
+	 * Constructs a new <code>ValueBoolean</code> object wrapping the specified <code>value</code>.
+	 * 
+	 * @param value the value to wrap
+	 */
+	public ValueBoolean(Boolean value) {
+		super(value);
+	}
+	
+	@Override
+	public Type getType() {
+		return TypePrimitive.BOOLEAN;
+	}
+	
+	@Override
+	public Value getDefaultValue() {
+		return new ValueBoolean(false);
+	}
+	
+	@Override
+	public ValueBoolean isLowerThan(Value value) {
+		sameTypesOrThrow(value, Operation.COMPARE);
+		if(isNull() || value.isNull())
+			return new ValueBoolean(null);
+		return new ValueBoolean(!getValue() && ((ValueBoolean)value).getValue());
+	}
+	
+	@Override
+	public ValueBoolean and(Value value) {
+		sameTypesOrThrow(value, Operation.AND);
+		if(isNull() || value.isNull())
+			return new ValueBoolean(null);
+		return new ValueBoolean(getValue() && ((ValueBoolean)value).getValue());
+	}
+	
+	@Override
+	public ValueBoolean or(Value value) { // -
+		sameTypesOrThrow(value, Operation.OR);
+		if(isNull() || value.isNull())
+			return new ValueBoolean(null);
+		return new ValueBoolean(getValue() || ((ValueBoolean)value).getValue());
+	}
+	
+	@Override
+	public ValueBoolean negate() { // !
+		return new ValueBoolean(isNull()? null : !getValue());
+	}
+	
+	@Override
+	public Value convertTo(Type type) {
+		switch(type.getPrimaryType()) {
+			case BOOLEAN:
+				return this;
+			case STRING:
+				return getValue() == null? ValueString.NULL_STRING : new ValueString(getValue().toString());
+			default:
+				throw new UnsupportedConversionException(getType(), type);
+		}
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueContact.java b/src/pl/edu/mimuw/cloudatlas/model/ValueContact.java
new file mode 100644
index 0000000..5101d17
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueContact.java
@@ -0,0 +1,100 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import java.net.InetAddress;
+
+import pl.edu.mimuw.cloudatlas.model.Value;
+import pl.edu.mimuw.cloudatlas.model.ValueContact;
+
+/**
+ * A class that represents a contact to a node. The contact consists of a full path name of this node and its IP
+ * address.
+ * <p>
+ * This class is immutable.
+ */
+public class ValueContact extends Value {
+	private final PathName name;
+	private final InetAddress address;
+	
+	/**
+	 * Constructs a new <code>ValueContact</code> with the specified path name and IP address.
+	 * 
+	 * @param name the full path name of a node
+	 * @param address the IP address of the node
+	 */
+	public ValueContact(PathName name, InetAddress address) {
+		this.name = name;
+		this.address = address;
+	}
+	
+	@Override
+	public Value getDefaultValue() {
+		return new ValueContact(null, null);
+	}
+	
+	/**
+	 * Returns a name stored in this object.
+	 * 
+	 * @return the name of a node
+	 */
+	public PathName getName() {
+		return name;
+	}
+	
+	/**
+	 * Returns an IP address stored in this object.
+	 * 
+	 * @return the IP address of a node
+	 */
+	public InetAddress getAddress() {
+		return address;
+	}
+	
+	@Override
+	public Type getType() {
+		return TypePrimitive.CONTACT;
+	}
+	
+	@Override
+	public Value convertTo(Type type) {
+		switch(type.getPrimaryType()) {
+			case CONTACT:
+				return this;
+			case STRING:
+				if(isNull())
+					return ValueString.NULL_STRING;
+				else
+					return new ValueString("(" + name.toString() + ", " + address.toString() + ")");
+			default:
+				throw new UnsupportedConversionException(getType(), type);
+		}
+	}
+	
+	@Override
+	public boolean isNull() {
+		return name == null || address == null;
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueDouble.java b/src/pl/edu/mimuw/cloudatlas/model/ValueDouble.java
new file mode 100644
index 0000000..b979f5f
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueDouble.java
@@ -0,0 +1,111 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import pl.edu.mimuw.cloudatlas.model.Value;
+import pl.edu.mimuw.cloudatlas.model.ValueDouble;
+
+/**
+ * A class that wraps a Java <code>Double</code> object.
+ */
+public class ValueDouble extends ValueSimple<Double> {
+	/**
+	 * Constructs a new <code>ValueDouble</code> object wrapping the specified <code>value</code>.
+	 * 
+	 * @param value the value to wrap
+	 */
+	public ValueDouble(Double value) {
+		super(value);
+	}
+	
+	@Override
+	public Type getType() {
+		return TypePrimitive.DOUBLE;
+	}
+	
+	@Override
+	public Value getDefaultValue() {
+		return new ValueDouble(0.0);
+	}
+	
+	@Override
+	public ValueBoolean isLowerThan(Value value) {
+		sameTypesOrThrow(value, Operation.COMPARE);
+		if(isNull() || value.isNull())
+			return new ValueBoolean(null);
+		return new ValueBoolean(getValue() < ((ValueDouble)value).getValue());
+	}
+	
+	@Override
+	public ValueDouble addValue(Value value) {
+		sameTypesOrThrow(value, Operation.ADD);
+		if(isNull() || value.isNull())
+			return new ValueDouble(null);
+		return new ValueDouble(getValue() + ((ValueDouble)value).getValue());
+	}
+	
+	@Override
+	public ValueDouble subtract(Value value) {
+		sameTypesOrThrow(value, Operation.SUBTRACT);
+		if(isNull() || value.isNull())
+			return new ValueDouble(null);
+		return new ValueDouble(getValue() - ((ValueDouble)value).getValue());
+	}
+	
+	@Override
+	public ValueDouble multiply(Value value) {
+		sameTypesOrThrow(value, Operation.MULTIPLY);
+		if(isNull() || value.isNull())
+			return new ValueDouble(null);
+		return new ValueDouble(getValue() * ((ValueDouble)value).getValue());
+	}
+	
+	@Override
+	public ValueDouble divide(Value value) {
+		sameTypesOrThrow(value, Operation.DIVIDE);
+		if(isNull() || value.isNull())
+			return new ValueDouble(null);
+		return new ValueDouble(getValue() / ((ValueDouble)value).getValue());
+	}
+	
+	@Override
+	public ValueDouble negate() {
+		return new ValueDouble(isNull()? null : -getValue());
+	}
+	
+	@Override
+	public Value convertTo(Type type) {
+		switch(type.getPrimaryType()) {
+			case DOUBLE:
+				return this;
+			case INT:
+				return new ValueInt(getValue() == null? null : getValue().longValue());
+			case STRING:
+				return getValue() == null? ValueString.NULL_STRING : new ValueString(getValue().toString());
+			default:
+				throw new UnsupportedConversionException(getType(), type);
+		}
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueDuration.java b/src/pl/edu/mimuw/cloudatlas/model/ValueDuration.java
new file mode 100644
index 0000000..12c2c73
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueDuration.java
@@ -0,0 +1,173 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+
+/**
+ * A class representing duration in milliseconds. The duration can be negative. This is a simple wrapper of a Java
+ * <code>Long</code> object.
+ */
+public class ValueDuration extends ValueSimple<Long> {
+	/**
+	 * Constructs a new <code>ValueDuration</code> object wrapping the specified <code>value</code>.
+	 * 
+	 * @param value the value to wrap
+	 */
+	public ValueDuration(Long value) {
+		super(value);
+	}
+	
+	@Override
+	public Type getType() {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+	
+	@Override
+	public Value getDefaultValue() {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+	
+	/**
+	 * Constructs a new <code>ValueDuration</code> object from the specified amounts of different time units.
+	 * 
+	 * @param seconds a number of full seconds
+	 * @param milliseconds a number of milliseconds (an absolute value does not have to be lower than 1000)
+	 */
+	public ValueDuration(long seconds, long milliseconds) {
+		this(seconds * 1000l + milliseconds);
+	}
+	
+	/**
+	 * Constructs a new <code>ValueDuration</code> object from the specified amounts of different time units.
+	 * 
+	 * @param minutes a number of full minutes
+	 * @param seconds a number of full seconds (an absolute value does not have to be lower than 60)
+	 * @param milliseconds a number of milliseconds (an absolute value does not have to be lower than 1000)
+	 */
+	public ValueDuration(long minutes, long seconds, long milliseconds) {
+		this(minutes * 60l + seconds, milliseconds);
+	}
+	
+	/**
+	 * Constructs a new <code>ValueDuration</code> object from the specified amounts of different time units.
+	 * 
+	 * @param hours a number of full hours
+	 * @param minutes a number of full minutes (an absolute value does not have to be lower than 60)
+	 * @param seconds a number of full seconds (an absolute value does not have to be lower than 60)
+	 * @param milliseconds a number of milliseconds (an absolute value does not have to be lower than 1000)
+	 */
+	public ValueDuration(long hours, long minutes, long seconds, long milliseconds) {
+		this(hours * 60l + minutes, seconds, milliseconds);
+	}
+	
+	/**
+	 * Constructs a new <code>ValueDuration</code> object from the specified amounts of different time units.
+	 * 
+	 * @param days a number of full days
+	 * @param hours a number of full hours (an absolute value does not have to be lower than 24)
+	 * @param minutes a number of full minutes (an absolute value does not have to be lower than 60)
+	 * @param seconds a number of full seconds (an absolute value does not have to be lower than 60)
+	 * @param milliseconds a number of milliseconds (an absolute value does not have to be lower than 1000)
+	 */
+	public ValueDuration(long days, long hours, long minutes, long seconds, long milliseconds) {
+		this(days * 24l + hours, minutes, seconds, milliseconds);
+	}
+	
+	/**
+	 * Constructs a new <code>ValueDuration</code> object from its textual representation. The representation has
+	 * format: <code>sd hh:mm:ss.lll</code> where:
+	 * <ul>
+	 * <li><code>s</code> is a sign (<code>+</code> or <code>-</code>),</li>
+	 * <li><code>d</code> is a number of days,</li>
+	 * <li><code>hh</code> is a number of hours (between <code>00</code> and <code>23</code>),</li>
+	 * <li><code>mm</code> is a number of minutes (between <code>00</code> and <code>59</code>),</li>
+	 * <li><code>ss</code> is a number of seconds (between <code>00</code> and <code>59</code>),</li>
+	 * <li><code>lll</code> is a number of milliseconds (between <code>000</code> and <code>999</code>).</li>
+	 * </ul>
+	 * <p>
+	 * All fields are obligatory.
+	 * 
+	 * @param value a textual representation of a duration
+	 * @throws IllegalArgumentException if <code>value</code> does not meet described rules
+	 */
+	public ValueDuration(String value) {
+		this(parseDuration(value));
+	}
+	
+	private static long parseDuration(String value) {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+	
+	@Override
+	public ValueBoolean isLowerThan(Value value) {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+	
+	@Override
+	public ValueDuration addValue(Value value) {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+	
+	@Override
+	public ValueDuration subtract(Value value) {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+	
+	@Override
+	public ValueDuration multiply(Value value) {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+	
+	@Override
+	public Value divide(Value value) {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+	
+	@Override
+	public ValueDuration modulo(Value value) {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+	
+	@Override
+	public ValueDuration negate() {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+	
+	@Override
+	public Value convertTo(Type type) {
+		// TODO
+		throw new UnsupportedOperationException("Not yet implemented");
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueInt.java b/src/pl/edu/mimuw/cloudatlas/model/ValueInt.java
new file mode 100644
index 0000000..d48532d
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueInt.java
@@ -0,0 +1,133 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import pl.edu.mimuw.cloudatlas.model.Type.PrimaryType;
+import pl.edu.mimuw.cloudatlas.model.Value;
+import pl.edu.mimuw.cloudatlas.model.ValueInt;
+
+/**
+ * A class that wraps a Java <code>Long</code> object.
+ */
+public class ValueInt extends ValueSimple<Long> {
+	/**
+	 * Constructs a new <code>ValueInt</code> object wrapping the specified <code>value</code>.
+	 * 
+	 * @param value the value to wrap
+	 */
+	public ValueInt(Long value) {
+		super(value);
+	}
+	
+	@Override
+	public Type getType() {
+		return TypePrimitive.INTEGER;
+	}
+	
+	@Override
+	public Value getDefaultValue() {
+		return new ValueInt(0l);
+	}
+	
+	@Override
+	public ValueBoolean isLowerThan(Value value) {
+		sameTypesOrThrow(value, Operation.COMPARE);
+		if(isNull() || value.isNull())
+			return new ValueBoolean(null);
+		return new ValueBoolean(getValue() < ((ValueInt)value).getValue());
+	}
+	
+	@Override
+	public ValueInt addValue(Value value) {
+		sameTypesOrThrow(value, Operation.ADD);
+		if(isNull() || value.isNull())
+			return new ValueInt(null);
+		return new ValueInt(getValue() + ((ValueInt)value).getValue());
+	}
+	
+	@Override
+	public ValueInt subtract(Value value) {
+		sameTypesOrThrow(value, Operation.SUBTRACT);
+		if(isNull() || value.isNull())
+			return new ValueInt(null);
+		return new ValueInt(getValue() - ((ValueInt)value).getValue());
+	}
+	
+	@Override
+	public Value multiply(Value value) {
+		if(value.getType().getPrimaryType() == PrimaryType.DURATION)
+			return value.multiply(this);
+		sameTypesOrThrow(value, Operation.MULTIPLY);
+		if(isNull() || value.isNull())
+			return new ValueInt(null);
+		return new ValueInt(getValue() * ((ValueInt)value).getValue());
+	}
+	
+	@Override
+	public ValueDouble divide(Value value) {
+		sameTypesOrThrow(value, Operation.DIVIDE);
+		if(value.isNull())
+			return new ValueDouble(null);
+		if(((ValueInt)value).getValue() == 0l)
+			throw new ArithmeticException("Division by zero.");
+		if(isNull())
+			return new ValueDouble(null);
+		return new ValueDouble((double)getValue() / ((ValueInt)value).getValue());
+	}
+	
+	@Override
+	public ValueInt modulo(Value value) {
+		sameTypesOrThrow(value, Operation.MODULO);
+		if(value.isNull())
+			return new ValueInt(null);
+		if(((ValueInt)value).getValue() == 0l)
+			throw new ArithmeticException("Division by zero.");
+		if(isNull())
+			return new ValueInt(null);
+		return new ValueInt(getValue() % ((ValueInt)value).getValue());
+	}
+	
+	@Override
+	public ValueInt negate() {
+		return new ValueInt(isNull()? null : -getValue());
+	}
+	
+	@Override
+	public Value convertTo(Type type) {
+		switch(type.getPrimaryType()) {
+			case DOUBLE:
+				return new ValueDouble(getValue() == null? null : getValue().doubleValue());
+			case DURATION:
+				return new ValueDuration(getValue());
+			case INT:
+				return this;
+			case STRING:
+				return getValue() == null? ValueString.NULL_STRING : new ValueString(Long.toString(getValue()
+						.longValue()));
+			default:
+				throw new UnsupportedConversionException(getType(), type);
+		}
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueList.java b/src/pl/edu/mimuw/cloudatlas/model/ValueList.java
new file mode 100644
index 0000000..d914736
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueList.java
@@ -0,0 +1,275 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+import java.util.Set;
+
+import pl.edu.mimuw.cloudatlas.model.TypeCollection;
+import pl.edu.mimuw.cloudatlas.model.Value;
+import pl.edu.mimuw.cloudatlas.model.ValueList;
+
+/**
+ * A value representing a list of values of the specified type. Implements <code>List</code> interface.
+ * <p>
+ * All constructors expect type of elements stored in this list. This type is checked when adding elements to the list
+ * and an <code>IllegalArgumentException</code> is thrown in case of error.
+ * 
+ * @see java.util.List
+ */
+public class ValueList extends ValueSimple<List<Value>> implements List<Value> {
+	private TypeCollection type;
+	
+	/**
+	 * Creates a new <code>ValueList</code> containing all the elements in the specified list.
+	 * 
+	 * @param value a list which content will be copied to this value
+	 * @param elementType type of elements stored in this list
+	 */
+	public ValueList(List<Value> value, Type elementType) {
+		this(elementType);
+		if(value != null)
+			setValue(value);
+	}
+	
+	/**
+	 * Creates an empty list.
+	 * 
+	 * @param elementType type of elements stored in this list
+	 */
+	public ValueList(Type elementType) {
+		super(new ArrayList<Value>());
+		type = new TypeCollection(Type.PrimaryType.LIST, elementType);
+	}
+	
+	@Override
+	public Type getType() {
+		return type;
+	}
+	
+	@Override
+	public Value getDefaultValue() {
+		return new ValueList(((TypeCollection)this.getType()).getElementType());
+	}
+	
+	/**
+	 * Gets a <code>List</code> containing all the objects stored in this value. Modifying a return value will cause an
+	 * exception.
+	 */
+	@Override
+	public List<Value> getValue() {
+		return getList() == null? null : Collections.unmodifiableList(getList());
+	}
+	
+	@Override
+	public ValueList addValue(Value value) {
+		sameTypesOrThrow(value, Operation.ADD);
+		if(isNull() || value.isNull())
+			return new ValueList(null, ((TypeCollection)getType()).getElementType());
+		List<Value> result = new ArrayList<Value>(getValue());
+		result.addAll(((ValueList)value).getValue());
+		return new ValueList(result, ((TypeCollection)getType()).getElementType());
+	}
+	
+	@Override
+	public Value convertTo(Type type) {
+		switch(type.getPrimaryType()) {
+			case LIST:
+				if(getType().isCompatible(type))
+					return this;
+				throw new UnsupportedConversionException(getType(), type);
+			case SET:
+				if(this.type.getElementType().isCompatible(((TypeCollection)type).getElementType())) {
+					if(this.isNull())
+						return new ValueSet(null, this.type.getElementType());
+					Set<Value> l = new HashSet<Value>();
+					l.addAll(this);
+					return new ValueSet(l, this.type.getElementType());
+				}
+				throw new UnsupportedConversionException(getType(), type);
+			case STRING:
+				return getValue() == null? ValueString.NULL_STRING : new ValueString(getValue().toString());
+			default:
+				throw new UnsupportedConversionException(getType(), type);
+		}
+	}
+	
+	@Override
+	public ValueInt valueSize() {
+		return new ValueInt((getList() == null? null : (long)getList().size()));
+	}
+	
+	@Override
+	public void setValue(List<Value> list) {
+		if(list == null)
+			super.setValue(null);
+		else {
+			super.setValue(new ArrayList<Value>());
+			for(Value e : list)
+				add(e);
+		}
+	}
+	
+	private List<Value> getList() {
+		return super.getValue();
+	}
+	
+	private void checkElement(Value element) {
+		if(element == null)
+			throw new IllegalArgumentException("If you want to use null, create an object containing null instead.");
+		if(!type.getElementType().isCompatible(element.getType()))
+			throw new IllegalArgumentException("This list contains elements of type "
+					+ type.getElementType().toString() + " only. Not compatibile with elements of type: "
+					+ element.getType().toString());
+	}
+	
+	@Override
+	public boolean add(Value e) {
+		checkElement(e);
+		return getList().add(e);
+	}
+	
+	@Override
+	public void add(int index, Value element) {
+		checkElement(element);
+		getList().add(index, element);
+	}
+	
+	@Override
+	public boolean addAll(Collection<? extends Value> c) {
+		for(Value e : c)
+			checkElement(e);
+		return getList().addAll(c);
+	}
+	
+	@Override
+	public boolean addAll(int index, Collection<? extends Value> c) {
+		for(Value e : c)
+			checkElement(e);
+		return getList().addAll(index, c);
+	}
+	
+	@Override
+	public void clear() {
+		getList().clear();
+	}
+	
+	@Override
+	public boolean contains(Object o) {
+		return getList().contains(o);
+	}
+	
+	@Override
+	public boolean containsAll(Collection<?> c) {
+		return getList().containsAll(c);
+	}
+	
+	@Override
+	public Value get(int index) {
+		return getList().get(index);
+	}
+	
+	@Override
+	public int indexOf(Object o) {
+		return getList().indexOf(o);
+	}
+	
+	@Override
+	public boolean isEmpty() {
+		return getList().isEmpty();
+	}
+	
+	@Override
+	public Iterator<Value> iterator() {
+		return getList().iterator();
+	}
+	
+	@Override
+	public int lastIndexOf(Object o) {
+		return getList().lastIndexOf(o);
+	}
+	
+	@Override
+	public ListIterator<Value> listIterator() {
+		return getList().listIterator();
+	}
+	
+	@Override
+	public ListIterator<Value> listIterator(int index) {
+		return getList().listIterator(index);
+	}
+	
+	@Override
+	public boolean remove(Object o) {
+		return getList().remove(o);
+	}
+	
+	@Override
+	public Value remove(int index) {
+		return getList().remove(index);
+	}
+	
+	@Override
+	public boolean removeAll(Collection<?> c) {
+		return getList().removeAll(c);
+	}
+	
+	@Override
+	public boolean retainAll(Collection<?> c) {
+		return getList().retainAll(c);
+	}
+	
+	@Override
+	public Value set(int index, Value element) {
+		checkElement(element);
+		return getList().set(index, element);
+	}
+	
+	@Override
+	public int size() {
+		return getList().size();
+	}
+	
+	@Override
+	public List<Value> subList(int fromIndex, int toIndex) {
+		return new ValueList(getList().subList(fromIndex, toIndex), type.getElementType());
+	}
+	
+	@Override
+	public Object[] toArray() {
+		return getList().toArray();
+	}
+	
+	@Override
+	public <Y> Y[] toArray(Y[] a) {
+		return getList().toArray(a);
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueNull.java b/src/pl/edu/mimuw/cloudatlas/model/ValueNull.java
new file mode 100644
index 0000000..e0c3f2a
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueNull.java
@@ -0,0 +1,155 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import pl.edu.mimuw.cloudatlas.model.Value;
+import pl.edu.mimuw.cloudatlas.model.ValueNull;
+
+/**
+ * A special null value of an unknown type introduced to deal with nulls. This class is a singleton.
+ * 
+ * @see TypePrimitve#NULL
+ * @see Type#isCompatible(Value)
+ */
+public class ValueNull extends Value {
+	private static ValueNull instance = null;
+	
+	private ValueNull() {}
+	
+	/**
+	 * Gets a singleton instance of a <code>ValueNull</code> class. Every call to this method returns the same
+	 * reference.
+	 * 
+	 * @return an instance of <code>ValueNull</code>
+	 */
+	public static ValueNull getInstance() {
+		if(instance == null)
+			instance = new ValueNull();
+		return instance;
+	}
+	
+	@Override
+	public Value getDefaultValue() {
+		return instance;
+	}
+	
+	@Override
+	public Value convertTo(Type type) {
+		switch(type.getPrimaryType()) {
+			case STRING:
+				return ValueString.NULL_STRING;
+			default:
+				return this;
+		}
+	}
+	
+	@Override
+	public Type getType() {
+		return TypePrimitive.NULL;
+	}
+	
+	@Override
+	public boolean isNull() {
+		return true;
+	}
+	
+	@Override
+	public Value isEqual(Value value) {
+		return new ValueBoolean(isNull() && value.isNull());
+	}
+	
+	@Override
+	public Value isLowerThan(Value value) {
+		if(value == getInstance())
+			return this;
+		return value.isLowerThan(this);
+	}
+	
+	@Override
+	public Value addValue(Value value) {
+		if(value == getInstance())
+			return this;
+		return value.addValue(this);
+	}
+	
+	@Override
+	public Value subtract(Value value) {
+		if(value == getInstance())
+			return this;
+		return value.subtract(this);
+	}
+	
+	@Override
+	public Value multiply(Value value) {
+		if(value == getInstance())
+			return this;
+		return value.multiply(this);
+	}
+	
+	@Override
+	public Value divide(Value value) {
+		if(value == getInstance())
+			return this;
+		return value.divide(this);
+	}
+	
+	@Override
+	public Value modulo(Value value) {
+		if(value == getInstance())
+			return this;
+		return value.modulo(this);
+	}
+	
+	@Override
+	public Value and(Value value) {
+		if(value == getInstance())
+			return this;
+		return value.and(this);
+	}
+	
+	@Override
+	public Value or(Value value) {
+		if(value == getInstance())
+			return this;
+		return value.or(this);
+	}
+	
+	@Override
+	public Value regExpr(Value value) {
+		if(value == getInstance())
+			return this;
+		return value.regExpr(this);
+	}
+	
+	@Override
+	public Value negate() {
+		return this;
+	}
+	
+	@Override
+	public Value valueSize() {
+		return this;
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueSet.java b/src/pl/edu/mimuw/cloudatlas/model/ValueSet.java
new file mode 100644
index 0000000..c91374d
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueSet.java
@@ -0,0 +1,232 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Set;
+
+import pl.edu.mimuw.cloudatlas.model.TypeCollection;
+import pl.edu.mimuw.cloudatlas.model.Value;
+import pl.edu.mimuw.cloudatlas.model.ValueSet;
+
+/**
+ * A value representing a set of values of the specified type. Implements <code>Set</code> interface.
+ * <p>
+ * All constructors expect type of elements stored in this set. This type is checked when adding elements to the set and
+ * an <code>IllegalArgumentException</code> is thrown in case of error.
+ * 
+ * @see java.util.Set
+ */
+public class ValueSet extends ValueSimple<Set<Value>> implements Set<Value> {
+	private TypeCollection type;
+	
+	/**
+	 * Creates a new <code>ValueSet</code> containing all the elements in the specified set.
+	 * 
+	 * @param value a set which content will be copied to this value
+	 * @param elementType type of elements stored in this set
+	 */
+	public ValueSet(Set<Value> value, Type elementType) {
+		this(elementType);
+		if(value != null)
+			setValue(value);
+	}
+	
+	/**
+	 * Creates an empty set.
+	 * 
+	 * @param elementType type of elements stored in this set
+	 */
+	public ValueSet(Type elementType) {
+		super(new HashSet<Value>());
+		type = new TypeCollection(Type.PrimaryType.SET, elementType);
+	}
+	
+	@Override
+	public Type getType() {
+		return type;
+	}
+	
+	@Override
+	public Value getDefaultValue() {
+		return new ValueSet(((TypeCollection)this.getType()).getElementType());
+	}
+	
+	/**
+	 * Gets a <code>Set</code> containing all the objects stored in this value. Modifying a return value will cause an
+	 * exception.
+	 */
+	@Override
+	public Set<Value> getValue() {
+		return getSet() == null? null : Collections.unmodifiableSet(getSet());
+	}
+	
+	@Override
+	public ValueSet addValue(Value value) {
+		sameTypesOrThrow(value, Operation.ADD);
+		if(isNull() || value.isNull())
+			return new ValueSet(null, ((TypeCollection)getType()).getElementType());
+		Set<Value> result = new HashSet<Value>(getValue());
+		result.addAll(((ValueSet)value).getValue());
+		return new ValueSet(result, ((TypeCollection)getType()).getElementType());
+	}
+	
+	@Override
+	public ValueInt valueSize() {
+		return new ValueInt((getSet() == null? null : (long)getSet().size()));
+	}
+	
+	@Override
+	public void setValue(Set<Value> set) {
+		if(set == null)
+			super.setValue(null);
+		else {
+			super.setValue(new HashSet<Value>());
+			for(Value e : set)
+				add(e);
+		}
+	}
+	
+	private Set<Value> getSet() {
+		return super.getValue();
+	}
+	
+	private void checkElement(Value element) {
+		if(element == null)
+			throw new IllegalArgumentException("If you want to use null, create an object containing null instead.");
+		if(!type.getElementType().isCompatible(element.getType()))
+			throw new IllegalArgumentException("This set contains elements of type " + type.getElementType().toString()
+					+ " only. Not compatibile with elements of type: " + element.getType().toString());
+	}
+	
+	@Override
+	public boolean add(Value e) {
+		checkElement(e);
+		return getSet().add(e);
+	}
+	
+	@Override
+	public boolean addAll(Collection<? extends Value> c) {
+		for(Value e : c)
+			checkElement(e);
+		return getSet().addAll(c);
+	}
+	
+	@Override
+	public void clear() {
+		getSet().clear();
+	}
+	
+	@Override
+	public boolean contains(Object o) {
+		return getSet().contains(o);
+	}
+	
+	@Override
+	public boolean containsAll(Collection<?> c) {
+		return getSet().containsAll(c);
+	}
+	
+	@Override
+	public boolean isEmpty() {
+		return getSet().isEmpty();
+	}
+	
+	@Override
+	public Iterator<Value> iterator() {
+		return getSet().iterator();
+	}
+	
+	@Override
+	public boolean remove(Object o) {
+		return getSet().remove(o);
+	}
+	
+	@Override
+	public boolean removeAll(Collection<?> c) {
+		return getSet().removeAll(c);
+	}
+	
+	@Override
+	public boolean retainAll(Collection<?> c) {
+		return getSet().retainAll(c);
+	}
+	
+	@Override
+	public int size() {
+		return getSet().size();
+	}
+	
+	@Override
+	public Object[] toArray() {
+		return getSet().toArray();
+	}
+	
+	@Override
+	public <U> U[] toArray(U[] a) {
+		return getSet().toArray(a);
+	}
+	
+	@Override
+	public Value convertTo(Type type) {
+		switch(type.getPrimaryType()) {
+			case SET:
+				if(getType().isCompatible(type))
+					return this;
+				throw new UnsupportedConversionException(getType(), type);
+			case LIST:
+				if(this.type.getElementType().isCompatible(((TypeCollection)type).getElementType())) {
+					if(this.isNull())
+						return new ValueList(null, this.type.getElementType());
+					List<Value> l = new ArrayList<Value>();
+					l.addAll(this);
+					return new ValueList(l, this.type.getElementType());
+				}
+				throw new UnsupportedConversionException(getType(), type);
+			case STRING:
+				if(getValue() == null)
+					return ValueString.NULL_STRING;
+				StringBuilder sb = new StringBuilder();
+				sb.append("{");
+				boolean notFirst = false;
+				for(Value v : getValue()) {
+					if(notFirst) {
+						sb.append(", ");
+					} else
+						notFirst = true;
+					sb.append(v.toString());
+				}
+				sb.append("}");
+				return new ValueString(sb.toString());
+			default:
+				throw new UnsupportedConversionException(getType(), type);
+		}
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueSimple.java b/src/pl/edu/mimuw/cloudatlas/model/ValueSimple.java
new file mode 100644
index 0000000..76d9062
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueSimple.java
@@ -0,0 +1,89 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+/**
+ * Convenient class for wrapping Java types into <code>Value</code> objects.
+ * <p>
+ * This class is immutable.
+ * 
+ * @param <T> a wrapped type
+ */
+abstract class ValueSimple<T> extends Value {
+	private T value;
+	
+	/**
+	 * Constructs a new <code>Value</code> wrapping the specified <code>value</code>.
+	 * 
+	 * @param value the value to wrap
+	 */
+	public ValueSimple(T value) {
+		setValue(value);
+	}
+	
+	/**
+	 * Returns a hash code value for this object. This is a hash code of underlying wrapped object.
+	 * 
+	 * @return the hash code for this value
+	 */
+	@Override
+	public int hashCode() {
+		return getValue().hashCode();
+	}
+	
+	/**
+	 * Gets a wrapped object.
+	 * 
+	 * @return the wrapped value
+	 */
+	public T getValue() {
+		return value;
+	}
+	
+	/**
+	 * Sets a wrapped value. This method is not public to ensure that the underlying value cannot be changed.
+	 * 
+	 * @param value the value to set
+	 */
+	void setValue(T value) {
+		this.value = value;
+	}
+	
+	@Override
+	public boolean isNull() {
+		return value == null;
+	}
+	
+	@SuppressWarnings("unchecked")
+	@Override
+	public Value isEqual(Value v) {
+		sameTypesOrThrow(v, Operation.EQUAL);
+		if(isNull() && v.isNull())
+			return new ValueBoolean(true);
+		else if(isNull() || v.isNull())
+			return new ValueBoolean(false);
+		return new ValueBoolean(value.equals(((ValueSimple<T>)v).getValue()));
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueString.java b/src/pl/edu/mimuw/cloudatlas/model/ValueString.java
new file mode 100644
index 0000000..34af8d1
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueString.java
@@ -0,0 +1,120 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import java.text.ParseException;
+
+import pl.edu.mimuw.cloudatlas.model.Value;
+import pl.edu.mimuw.cloudatlas.model.ValueString;
+
+/**
+ * A class that wraps a Java <code>String</code> object.
+ */
+public class ValueString extends ValueSimple<String> {
+	/**
+	 * A result of conversion values representing null to <code>ValueString</code>.
+	 */
+	protected static final ValueString NULL_STRING = new ValueString("NULL");
+	
+	/**
+	 * Constructs a new <code>ValueString</code> object wrapping the specified <code>value</code>.
+	 * 
+	 * @param value the value to wrap
+	 */
+	public ValueString(String value) {
+		super(value);
+	}
+	
+	@Override
+	public Type getType() {
+		return TypePrimitive.STRING;
+	}
+	
+	@Override
+	public Value getDefaultValue() {
+		return new ValueString("");
+	}
+	
+	@Override
+	public ValueBoolean isLowerThan(Value value) {
+		sameTypesOrThrow(value, Operation.COMPARE);
+		if(isNull() || value.isNull())
+			return new ValueBoolean(null);
+		return new ValueBoolean(getValue().compareTo(((ValueString)value).getValue()) < 0);
+	}
+	
+	@Override
+	public ValueString addValue(Value value) {
+		sameTypesOrThrow(value, Operation.ADD);
+		if(isNull() || value.isNull())
+			return new ValueString(null);
+		return new ValueString(getValue().concat(((ValueString)value).getValue()));
+	}
+	
+	@Override
+	public ValueBoolean regExpr(Value value) {
+		sameTypesOrThrow(value, Operation.REG_EXPR);
+		if(isNull() || value.isNull())
+			return new ValueBoolean(null);
+		return new ValueBoolean(getValue().matches(((ValueString)value).getValue()));
+	}
+	
+	@Override
+	public Value convertTo(Type type) {
+		switch(type.getPrimaryType()) {
+			case BOOLEAN:
+				return new ValueBoolean(Boolean.parseBoolean(getValue()));
+			case DOUBLE:
+				try {
+					return new ValueDouble(Double.parseDouble(getValue()));
+				} catch(NumberFormatException exception) {
+					return new ValueDouble(null);
+				}
+			case DURATION:
+				return new ValueDuration(getValue());
+			case INT:
+				try {
+					return new ValueInt(Long.parseLong(getValue()));
+				} catch(NumberFormatException exception) {
+					return new ValueInt(null);
+				}
+			case STRING:
+				return getValue() == null? ValueString.NULL_STRING : this;
+			case TIME:
+				try {
+					return new ValueTime(getValue());
+				} catch(ParseException exception) {
+					return new ValueTime((Long)null);
+				}
+			default:
+				throw new UnsupportedConversionException(getType(), type);
+		}
+	}
+	
+	@Override
+	public ValueInt valueSize() {
+		return new ValueInt(getValue() == null? null : (long)getValue().length());
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ValueTime.java b/src/pl/edu/mimuw/cloudatlas/model/ValueTime.java
new file mode 100644
index 0000000..f494757
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ValueTime.java
@@ -0,0 +1,117 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import java.text.DateFormat;
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+
+import pl.edu.mimuw.cloudatlas.model.Value;
+import pl.edu.mimuw.cloudatlas.model.ValueTime;
+
+/**
+ * A class representing the POSIX time in milliseconds. This is a simple wrapper of a Java <code>Long</code> object.
+ */
+public class ValueTime extends ValueSimple<Long> {
+	/**
+	 * A format of string representing <code>ValueTime</code> when constructing from or converting to a
+	 * <code>String</code> object.
+	 */
+	public static final DateFormat TIME_FORMAT = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss.SSS");
+	
+	/**
+	 * Constructs a new <code>ValueTime</code> object wrapping the specified value.
+	 * 
+	 * @param value the POSIX time
+	 */
+	public ValueTime(Long value) {
+		super(value);
+	}
+	
+	@Override
+	public Type getType() {
+		return TypePrimitive.TIME;
+	}
+	
+	@Override
+	public Value getDefaultValue() {
+		return new ValueTime(0l);
+	}
+	
+	/**
+	 * Constructs a new <code>ValueTime</code> object from its textual representation.
+	 * 
+	 * @param time a time formatted according to {@link #TIME_FORMAT}
+	 * @throws ParseException if the <code>time</code> is incorrect
+	 * @see #TIME_FORMAT
+	 */
+	public ValueTime(String time) throws ParseException {
+		this(TIME_FORMAT.parse(time).getTime());
+	}
+	
+	@Override
+	public ValueBoolean isLowerThan(Value value) {
+		sameTypesOrThrow(value, Operation.COMPARE);
+		if(isNull() || value.isNull())
+			return new ValueBoolean(null);
+		return new ValueBoolean(getValue() < ((ValueTime)value).getValue());
+	}
+	
+	@Override
+	public ValueTime addValue(Value value) {
+		if(!value.getType().isCompatible(TypePrimitive.DURATION))
+			throw new IncompatibleTypesException(getType(), value.getType(), Operation.ADD);
+		if(isNull() || value.isNull())
+			return new ValueTime((Long)null);
+		return new ValueTime(getValue() + ((ValueDuration)value).getValue());
+	}
+	
+	@Override
+	public Value subtract(Value value) {
+		if(value.getType().isCompatible(TypePrimitive.DURATION)) {
+			if(isNull() || value.isNull())
+				return new ValueTime((Long)null);
+			return new ValueTime(getValue() - ((ValueDuration)value).getValue());
+		} else if(value.getType().isCompatible(TypePrimitive.TIME)) {
+			if(isNull() || value.isNull())
+				return new ValueTime((Long)null);
+			return new ValueDuration(getValue() - ((ValueTime)value).getValue());
+		}
+		throw new IncompatibleTypesException(getType(), value.getType(), Operation.SUBTRACT);
+		
+	}
+	
+	@Override
+	public Value convertTo(Type type) {
+		switch(type.getPrimaryType()) {
+			case STRING:
+				return getValue() == null? ValueString.NULL_STRING : new ValueString(TIME_FORMAT.format(getValue()));
+			case TIME:
+				return this;
+			default:
+				throw new UnsupportedConversionException(getType(), type);
+		}
+	}
+}
diff --git a/src/pl/edu/mimuw/cloudatlas/model/ZMI.java b/src/pl/edu/mimuw/cloudatlas/model/ZMI.java
new file mode 100644
index 0000000..0e1c852
--- /dev/null
+++ b/src/pl/edu/mimuw/cloudatlas/model/ZMI.java
@@ -0,0 +1,166 @@
+/**
+ * Copyright (c) 2014, University of Warsaw
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification, are permitted
+ * provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this list of
+ * conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+ * conditions and the following disclaimer in the documentation and/or other materials provided
+ * with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+ * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
+ * WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package pl.edu.mimuw.cloudatlas.model;
+
+import java.io.PrintStream;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map.Entry;
+
+/**
+ * A zone management information. This object is a single node in a zone hierarchy. It stores zone attributes as well as
+ * references to its father and sons in the tree.
+ */
+public class ZMI implements Cloneable {
+	private final AttributesMap attributes = new AttributesMap();
+	
+	private final List<ZMI> sons = new ArrayList<ZMI>();
+	private ZMI father;
+	
+	/**
+	 * Creates a new ZMI with no father (the root zone) and empty sons list.
+	 */
+	public ZMI() {
+		this(null);
+	}
+	
+	/**
+	 * Creates a new ZMI with the specified node as a father and empty sons list. This method does not perform any
+	 * operation on the <code>father</code>. Especially, setting this object as a <code>father</code>'s son must be done
+	 * separately.
+	 * 
+	 * @param father a father of this ZMI
+	 * @see #addSon(ZMI)
+	 */
+	public ZMI(ZMI father) {
+		this.father = father;
+	}
+	
+	/**
+	 * Gets a father of this ZMI in a tree.
+	 * 
+	 * @return a father of this ZMI or <code>null</code> if this is the root zone
+	 */
+	public ZMI getFather() {
+		return father;
+	}
+	
+	/**
+	 * Sets or changes a father of this ZMI in a tree. This method does not perform any operation on the
+	 * <code>father</code>. Especially, setting this object as a <code>father</code>'s son must be done separately.
+	 * 
+	 * @param father a new father for this ZMI
+	 * @see #addSon(ZMI)
+	 */
+	public void setFather(ZMI father) {
+		this.father = father;
+	}
+	
+	/**
+	 * Gets a list of sons of this ZMI in a tree. Modifying a return value will cause an exception.
+	 * 
+	 * @return
+	 */
+	public List<ZMI> getSons() {
+		return Collections.unmodifiableList(sons);
+	}
+	
+	/**
+	 * Adds the specified ZMI to the list of sons of this ZMI. This method does not perform any operation on a
+	 * <code>son</code>. Especially, setting this object as a <code>son</code>'s father must be done separately.
+	 * 
+	 * @param son
+	 * @see #ZMI(ZMI)
+	 * @see #setFather(ZMI)
+	 */
+	public void addSon(ZMI son) {
+		sons.add(son);
+	}
+	
+	/**
+	 * Removes the specified ZMI from the list of sons of this ZMI. This method does not perform any operation on a
+	 * <code>son</code>. Especially, its father remains unchanged.
+	 * 
+	 * @param son
+	 * @see #setFather(ZMI)
+	 */
+	public void removeSon(ZMI son) {
+		sons.remove(son);
+	}
+	
+	/**
+	 * Gets a map of all the attributes stored in this ZMI.
+	 * 
+	 * @return map of attributes
+	 */
+	public AttributesMap getAttributes() {
+		return attributes;
+	}
+	
+	/**
+	 * Prints recursively in a prefix order (starting from this ZMI) a whole tree with all the attributes.
+	 * 
+	 * @param stream a destination stream
+	 * @see #toString()
+	 */
+	public void printAttributes(PrintStream stream) {
+		for(Entry<Attribute, Value> entry : attributes)
+			stream.println(entry.getKey() + " : " + entry.getValue().getType() + " = " + entry.getValue());
+		System.out.println();
+		for(ZMI son : sons)
+			son.printAttributes(stream);
+	}
+	
+	/**
+	 * Creates an independent copy of a whole hierarchy. A returned ZMI has the same reference as a father (but the
+	 * father does not have a reference to it as a son). For the root zone, the copy is completely independent, since
+	 * its father is <code>null</code>.
+	 * 
+	 * @return a deep copy of this ZMI
+	 */
+	@Override
+	public ZMI clone() {
+		ZMI result = new ZMI(father);
+		result.attributes.add(attributes.clone());
+		for(ZMI son : sons) {
+			ZMI sonClone = son.clone();
+			result.sons.add(sonClone);
+			sonClone.father = result;
+		}
+		return result;
+	}
+	
+	/**
+	 * Prints a textual representation of this ZMI. It contains only attributes of this node.
+	 * 
+	 * @return a textual representation of this object
+	 * @see #printAttributes(PrintStream)
+	 */
+	@Override
+	public String toString() {
+		return attributes.toString();
+	}
+}