DirectTypeHierarchyInferencer.java

/*
 * Copyright Aduna (http://www.aduna-software.com/) (c) 1997-2007.
 *
 * Licensed under the Aduna BSD-style license.
 */
package org.openrdf.sail.inferencer.fc;

import java.util.Collection;
import java.util.HashSet;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import info.aduna.iteration.CloseableIteration;

import org.openrdf.model.Resource;
import org.openrdf.model.Statement;
import org.openrdf.model.URI;
import org.openrdf.model.Value;
import org.openrdf.model.ValueFactory;
import org.openrdf.model.vocabulary.RDF;
import org.openrdf.model.vocabulary.RDFS;
import org.openrdf.model.vocabulary.SESAME;
import org.openrdf.query.BindingSet;
import org.openrdf.query.MalformedQueryException;
import org.openrdf.query.QueryEvaluationException;
import org.openrdf.query.QueryLanguage;
import org.openrdf.query.impl.EmptyBindingSet;
import org.openrdf.query.parser.ParsedGraphQuery;
import org.openrdf.query.parser.QueryParserUtil;
import org.openrdf.rio.RDFHandlerException;
import org.openrdf.sail.Sail;
import org.openrdf.sail.SailConnectionListener;
import org.openrdf.sail.SailException;
import org.openrdf.sail.helpers.SailWrapper;
import org.openrdf.sail.inferencer.InferencerConnection;
import org.openrdf.sail.inferencer.InferencerConnectionWrapper;

/**
 * A forward-chaining inferencer that infers the direct-type hierarchy relations
 * {@link SESAME#DIRECTSUBCLASSOF sesame:directSubClassOf},
 * {@link SESAME#DIRECTSUBPROPERTYOF sesame:directSubPropertyOf} and
 * {@link SESAME#DIRECTTYPE sesame:directType}.
 * <p>
 * The semantics of this inferencer are defined as follows:
 * 
 * <pre>
 *    Class A is a direct subclass of B iff:
 *       1. A is a subclass of B and;
 *       2. A and B are not equa and;
 *       3. there is no class C (unequal A and B) such that 
 *          A is a subclass of C and C of B.
 *   
 *    Property P is a direct subproperty of Q iff:
 *       1. P is a subproperty of Q and;
 *       2. P and Q are not equal and;
 *       3. there is no property R (unequal P and Q) such that
 *          P is a subproperty of R and R of Q.
 *   
 *    Resource I is of direct type T iff:
 *       1. I is of type T and
 *       2. There is no class U (unequal T) such that:
 *           a. U is a subclass of T and;
 *           b. I is of type U.
 * </pre>
 */
public class DirectTypeHierarchyInferencer extends SailWrapper {

	protected final Logger logger = LoggerFactory.getLogger(this.getClass());

	/*-----------*
	 * Constants * 
	 *-----------*/

	private static final ParsedGraphQuery DIRECT_SUBCLASSOF_MATCHER;

	private static final ParsedGraphQuery DIRECT_SUBCLASSOF_QUERY;

	private static final ParsedGraphQuery DIRECT_SUBPROPERTYOF_MATCHER;

	private static final ParsedGraphQuery DIRECT_SUBPROPERTYOF_QUERY;

	private static final ParsedGraphQuery DIRECT_TYPE_MATCHER;

	private static final ParsedGraphQuery DIRECT_TYPE_QUERY;

	static {
		try {
			DIRECT_SUBCLASSOF_MATCHER = QueryParserUtil.parseGraphQuery(QueryLanguage.SERQL,
					"CONSTRUCT * FROM {X} sesame:directSubClassOf {Y} ", null);

			DIRECT_SUBPROPERTYOF_MATCHER = QueryParserUtil.parseGraphQuery(QueryLanguage.SERQL,
					"CONSTRUCT * FROM {X} sesame:directType {Y}", null);

			DIRECT_TYPE_MATCHER = QueryParserUtil.parseGraphQuery(QueryLanguage.SERQL,
					"CONSTRUCT * FROM {X} sesame:directSubPropertyOf {Y}", null);

			DIRECT_SUBCLASSOF_QUERY = QueryParserUtil.parseGraphQuery(
					QueryLanguage.SERQL,
					"CONSTRUCT {X} sesame:directSubClassOf {Y} "
							+ "FROM {X} rdfs:subClassOf {Y} "
							+ "WHERE X != Y AND "
							+ "NOT EXISTS (SELECT Z FROM {X} rdfs:subClassOf {Z} rdfs:subClassOf {Y} WHERE X != Z AND Z != Y)",
					null);

			DIRECT_SUBPROPERTYOF_QUERY = QueryParserUtil.parseGraphQuery(
					QueryLanguage.SERQL,
					"CONSTRUCT {X} sesame:directSubPropertyOf {Y} "
							+ "FROM {X} rdfs:subPropertyOf {Y} "
							+ "WHERE X != Y AND "
							+ "NOT EXISTS (SELECT Z FROM {X} rdfs:subPropertyOf {Z} rdfs:subPropertyOf {Y} WHERE X != Z AND Z != Y)",
					null);

			DIRECT_TYPE_QUERY = QueryParserUtil.parseGraphQuery(QueryLanguage.SERQL,
					"CONSTRUCT {X} sesame:directType {Y} FROM {X} rdf:type {Y} "
							+ "WHERE NOT EXISTS (SELECT Z FROM {X} rdf:type {Z} rdfs:subClassOf {Y} WHERE Z != Y)",
					null);
		}
		catch (MalformedQueryException e) {
			// Can only occur due to a bug in this code
			throw new RuntimeException(e);
		}
	}

	/*--------------*
	 * Constructors * 
	 *--------------*/

	public DirectTypeHierarchyInferencer() {
		super();
	}

	public DirectTypeHierarchyInferencer(Sail baseSail) {
		super(baseSail);
	}

	/*---------*
	 * Methods * 
	 *---------*/

	@Override
	public InferencerConnection getConnection()
		throws SailException
	{
		try {
			InferencerConnection con = (InferencerConnection)super.getConnection();
			return new DirectTypeHierarchyInferencerConnection(con);
		}
		catch (ClassCastException e) {
			throw new SailException(e.getMessage(), e);
		}
	}

	public void initialize()
		throws SailException
	{
		super.initialize();

		InferencerConnection con = getConnection();
		try {
			con.flushUpdates();
			con.commit();
		}
		finally {
			con.close();
		}
	}

	/*-----------------------------------------------------*
	 * Inner class DirectTypeHierarchyInferencerConnection *
	 *-----------------------------------------------------*/

	private class DirectTypeHierarchyInferencerConnection extends InferencerConnectionWrapper implements
			SailConnectionListener
	{

		/**
		 * Flag indicating whether an update of the inferred statements is needed.
		 */
		private boolean updateNeeded = false;

		public DirectTypeHierarchyInferencerConnection(InferencerConnection con) {
			super(con);
			con.addConnectionListener(this);
		}

		// called by base sail
		public void statementAdded(Statement st) {
			checkUpdatedStatement(st);
		}

		// called by base sail
		public void statementRemoved(Statement st) {
			checkUpdatedStatement(st);
		}

		private void checkUpdatedStatement(Statement st) {
			URI pred = st.getPredicate();

			if (pred.equals(RDF.TYPE) || pred.equals(RDFS.SUBCLASSOF) || pred.equals(RDFS.SUBPROPERTYOF)) {
				updateNeeded = true;
			}
		}

		@Override
		public void rollback()
			throws SailException
		{
			updateNeeded = false;
			super.rollback();
		}

		@Override
		public void flushUpdates()
			throws SailException
		{
			super.flushUpdates();

			if (!updateNeeded) {
				return;
			}

			try {
				// Determine which statements should be added and which should be
				// removed
				Collection<Statement> oldStatements = new HashSet<Statement>(256);
				Collection<Statement> newStatements = new HashSet<Statement>(256);

				evaluateIntoStatements(DIRECT_SUBCLASSOF_MATCHER, oldStatements);
				evaluateIntoStatements(DIRECT_SUBPROPERTYOF_MATCHER, oldStatements);
				evaluateIntoStatements(DIRECT_TYPE_MATCHER, oldStatements);

				evaluateIntoStatements(DIRECT_SUBCLASSOF_QUERY, newStatements);
				evaluateIntoStatements(DIRECT_SUBPROPERTYOF_QUERY, newStatements);
				evaluateIntoStatements(DIRECT_TYPE_QUERY, newStatements);

				logger.debug("existing virtual properties: {}", oldStatements.size());
				logger.debug("new virtual properties: {}", newStatements.size());

				// Remove the statements that should be retained from both sets
				Collection<Statement> unchangedStatements = new HashSet<Statement>(oldStatements);
				unchangedStatements.retainAll(newStatements);

				oldStatements.removeAll(unchangedStatements);
				newStatements.removeAll(unchangedStatements);

				logger.debug("virtual properties to remove: {}", oldStatements.size());
				logger.debug("virtual properties to add: {}", newStatements.size());

				Resource[] contexts = new Resource[] { null };

				for (Statement st : oldStatements) {
					removeInferredStatement(st.getSubject(), st.getPredicate(), st.getObject(), contexts);
				}

				for (Statement st : newStatements) {
					addInferredStatement(st.getSubject(), st.getPredicate(), st.getObject(), contexts);
				}

				updateNeeded = false;
			}
			catch (RDFHandlerException e) {
				Throwable t = e.getCause();
				if (t instanceof SailException) {
					throw (SailException)t;
				}
				else {
					throw new SailException(t);
				}
			}
			catch (QueryEvaluationException e) {
				throw new SailException(e);
			}
		}

		private void evaluateIntoStatements(ParsedGraphQuery query, Collection<Statement> statements)
			throws SailException, RDFHandlerException, QueryEvaluationException
		{
			CloseableIteration<? extends BindingSet, QueryEvaluationException> bindingsIter = getWrappedConnection().evaluate(
					query.getTupleExpr(), null, EmptyBindingSet.getInstance(), true);

			try {
				ValueFactory vf = getValueFactory();

				while (bindingsIter.hasNext()) {
					BindingSet bindings = bindingsIter.next();

					Value subj = bindings.getValue("subject");
					Value pred = bindings.getValue("predicate");
					Value obj = bindings.getValue("object");

					if (subj instanceof Resource && pred instanceof URI && obj != null) {
						statements.add(vf.createStatement((Resource)subj, (URI)pred, obj));
					}
				}
			}
			finally {
				bindingsIter.close();
			}
		}
	} // end inner class DirectTypeHierarchyInferencerConnection
}