/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.rya.rdftriplestore.inference;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.Stack;
import java.util.Timer;
import java.util.TimerTask;
import java.util.TreeMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.locks.ReentrantLock;

import org.apache.commons.lang3.mutable.MutableObject;
import org.apache.log4j.Logger;
import org.apache.rya.api.RdfCloudTripleStoreConfiguration;
import org.apache.rya.api.persist.RyaDAO;
import org.apache.rya.api.persist.RyaDAOException;
import org.apache.rya.api.persist.utils.RyaDAOHelper;
import org.apache.rya.api.persist.utils.RyaDaoQueryWrapper;
import org.apache.tinkerpop.gremlin.structure.Direction;
import org.apache.tinkerpop.gremlin.structure.Graph;
import org.apache.tinkerpop.gremlin.structure.T;
import org.apache.tinkerpop.gremlin.structure.Vertex;
import org.apache.tinkerpop.gremlin.tinkergraph.structure.TinkerGraph;
import org.eclipse.rdf4j.common.iteration.CloseableIteration;
import org.eclipse.rdf4j.model.IRI;
import org.eclipse.rdf4j.model.Resource;
import org.eclipse.rdf4j.model.Statement;
import org.eclipse.rdf4j.model.Value;
import org.eclipse.rdf4j.model.ValueFactory;
import org.eclipse.rdf4j.model.impl.SimpleValueFactory;
import org.eclipse.rdf4j.model.vocabulary.OWL;
import org.eclipse.rdf4j.model.vocabulary.RDF;
import org.eclipse.rdf4j.model.vocabulary.RDFS;
import org.eclipse.rdf4j.query.QueryEvaluationException;
import org.eclipse.rdf4j.rio.RDFHandlerException;
import org.eclipse.rdf4j.rio.helpers.AbstractRDFHandler;

import com.google.common.collect.Sets;

/**
 * Will pull down inference relationships from dao every x seconds. <br>
 * Will infer extra relationships. <br>
 * Will cache relationships in Graph for later use. <br>
 */
public class InferenceEngine {
    private static final Logger log = Logger.getLogger(InferenceEngine.class);
    private static final ValueFactory VF = SimpleValueFactory.getInstance();
    private static final IRI HAS_SELF = VF.createIRI(OWL.NAMESPACE, "hasSelf");
    private static final IRI REFLEXIVE_PROPERTY = VF.createIRI(OWL.NAMESPACE, "ReflexiveProperty");
    public static final String URI_PROP = "uri";

    private final ReentrantLock refreshLock = new ReentrantLock();

    private final AtomicReference<Graph> subClassOfGraph = new AtomicReference<>();
    private final AtomicReference<Graph> subPropertyOfGraph = new AtomicReference<>();

    private final Set<IRI> symmetricPropertySet = ConcurrentHashMap.newKeySet();;
    private final Map<IRI, IRI> inverseOfMap = new ConcurrentHashMap<>();
    private final Set<IRI> transitivePropertySet = ConcurrentHashMap.newKeySet();;
    private final Set<IRI> reflexivePropertySet = ConcurrentHashMap.newKeySet();;
    private final Map<IRI, Set<IRI>> domainByType = new ConcurrentHashMap<>();
    private final Map<IRI, Set<IRI>> rangeByType = new ConcurrentHashMap<>();
    private final Map<Resource, Map<IRI, Value>> hasValueByType = new ConcurrentHashMap<>();
    private final Map<IRI, Map<Resource, Value>> hasValueByProperty = new ConcurrentHashMap<>();
    private final Map<Resource, Map<Resource, IRI>> someValuesFromByRestrictionType = new ConcurrentHashMap<>();
    private final Map<Resource, Map<Resource, IRI>> allValuesFromByValueType = new ConcurrentHashMap<>();
    private final Map<Resource, List<Set<Resource>>> intersections = new ConcurrentHashMap<>();
    private final Map<Resource, Set<Resource>> enumerations = new ConcurrentHashMap<>();
    private final Map<IRI, List<IRI>> propertyChainPropertyToChain = new ConcurrentHashMap<>();
    // hasSelf maps.
    private final Map<IRI, Set<Resource>> hasSelfByProperty = new ConcurrentHashMap<>();
    private final Map<Resource, Set<IRI>> hasSelfByType = new ConcurrentHashMap<>();

    private RyaDAO<?> ryaDAO;
    private RdfCloudTripleStoreConfiguration conf;
    private RyaDaoQueryWrapper ryaDaoQueryWrapper;
    private final AtomicBoolean isInitialized = new AtomicBoolean();
    private final AtomicBoolean schedule = new AtomicBoolean(true);

    private final AtomicLong refreshGraphSchedule = new AtomicLong(5 * 60 * 1000); //5 min
    private Timer timer;

    public void init() throws InferenceEngineException {
        try {
            if (isInitialized()) {
                return;
            }

            checkNotNull(conf, "Configuration is null");
            checkNotNull(ryaDAO, "RdfDao is null");
            checkArgument(ryaDAO.isInitialized(), "RdfDao is not initialized");
            ryaDaoQueryWrapper = new RyaDaoQueryWrapper(ryaDAO, conf);

            refreshGraph();

            if (schedule.get()) {
                timer = new Timer(InferenceEngine.class.getName());
                timer.scheduleAtFixedRate(new TimerTask() {
                    @Override
                    public void run() {
                        try {
                            refreshGraph();
                        } catch (final InferenceEngineException e) {
                            throw new RuntimeException(e);
                        }
                    }
                }, refreshGraphSchedule.get(), refreshGraphSchedule.get());
            }

            setInitialized(true);
        } catch (final RyaDAOException e) {
            throw new InferenceEngineException(e);
        }
    }

    public void destroy() throws InferenceEngineException {
        setInitialized(false);
        if (timer != null) {
            timer.cancel();
        }
    }

    public void refreshGraph() throws InferenceEngineException {
        refreshLock.lock();
        try {
            //get all subclassof
            Graph graph = TinkerGraph.open();
            addPredicateEdges(RDFS.SUBCLASSOF, Direction.OUT, graph, RDFS.SUBCLASSOF.stringValue());
            //equivalentClass is the same as subClassOf both ways
            addPredicateEdges(OWL.EQUIVALENTCLASS, Direction.BOTH, graph, RDFS.SUBCLASSOF.stringValue());
            // Add unions to the subclass graph
            addUnions(graph);
            subClassOfGraph.set(graph);

            graph = TinkerGraph.open();
            addPredicateEdges(RDFS.SUBPROPERTYOF, Direction.OUT, graph, RDFS.SUBPROPERTYOF.stringValue());
            //equiv property really is the same as a subPropertyOf both ways
            addPredicateEdges(OWL.EQUIVALENTPROPERTY, Direction.BOTH, graph, RDFS.SUBPROPERTYOF.stringValue());
            subPropertyOfGraph.set(graph);

            refreshIntersectionOf();

            refreshOneOf();

            synchronized(symmetricPropertySet) {
                symmetricPropertySet.clear();
                symmetricPropertySet.addAll(fetchInstances(OWL.SYMMETRICPROPERTY));
            }
            synchronized(transitivePropertySet) {
                transitivePropertySet.clear();
                transitivePropertySet.addAll(fetchInstances(OWL.TRANSITIVEPROPERTY));
            }
            synchronized(reflexivePropertySet) {
                reflexivePropertySet.clear();
                reflexivePropertySet.addAll(fetchInstances(REFLEXIVE_PROPERTY));
            }

            refreshInverseOf();

            refreshPropertyChainPropertyToChain();

            refreshDomainRange();

            refreshPropertyRestrictions();
        } catch (final QueryEvaluationException e) {
            throw new InferenceEngineException(e);
        } finally {
            refreshLock.unlock();
        }
    }

    /**
     * Query for and collect all instances of a given type. Should only be called for types expected
     * to have few members, such as ontology vocabulary terms, as instances will be collected in
     * memory.
     */
    private Set<IRI> fetchInstances(final IRI type) throws QueryEvaluationException {
        final Set<IRI> instances = new HashSet<>();
        ryaDaoQueryWrapper.queryAll(null, RDF.TYPE, type, new AbstractRDFHandler() {
            @Override
            public void handleStatement(final Statement st) throws RDFHandlerException {
                if (st.getSubject() instanceof IRI) {
                    instances.add((IRI) st.getSubject());
                }
            }
        });
        return instances;
    }

    /**
     * Query for all triples involving a given predicate and add corresponding edges to a
     * {@link Graph} in one or both directions.
     * @param predicate Find all connections via this predicate URI
     * @param dir Direction of interest: for a matching triple, if {@link Direction#OUT} add an edge
     *      from subject to object; if {@link Direction#IN} add an edge from object to subject;
     *      if {@link Direction#BOTH} add both.
     * @param graph A TinkerPop graph
     * @param edgeName Label that will be given to all added edges
     * @throws QueryEvaluationException
     */
    private void addPredicateEdges(final IRI predicate, final Direction dir, final Graph graph, final String edgeName)
            throws QueryEvaluationException {
        final CloseableIteration<Statement, QueryEvaluationException> iter = RyaDAOHelper.query(ryaDAO,
                null, predicate, null, conf);
        try {
            while (iter.hasNext()) {
                final Statement st = iter.next();
                if (Direction.OUT.equals(dir) || Direction.BOTH.equals(dir)) {
                    addStatementEdge(graph, edgeName, st);
                }
                if (Direction.IN.equals(dir) || Direction.BOTH.equals(dir)) {
                    addStatementEdge(graph, edgeName, VF.createStatement((Resource) st.getObject(),
                            st.getPredicate(), st.getSubject()));
                }
            }
        } finally {
            if (iter != null) {
                iter.close();
            }
        }
    }

    /**
     * Add unions to the subclass graph: if c owl:unionOf LIST(c1, c2, ... cn),
     * then any instances of c1, c2, ... or cn are also instances of c, meaning
     * c is a superclass of all the rest.
     * (In principle, an instance of c is likewise implied to be at least one of
     * the other types, but this fact is ignored for now to avoid
     * nondeterministic reasoning.)
     * @param graph the {@link Graph} to add to.
     * @throws QueryEvaluationException
     */
    private void addUnions(final Graph graph) throws QueryEvaluationException {
        final CloseableIteration<Statement, QueryEvaluationException> iter = RyaDAOHelper.query(ryaDAO, null, OWL.UNIONOF, null, conf);
        try {
            while (iter.hasNext()) {
                final Statement st = iter.next();
                final Value unionType = st.getSubject();
                // Traverse the list of types constituting the union
                Value current = st.getObject();
                while (current instanceof Resource && !RDF.NIL.equals(current)) {
                    final Resource listNode = (Resource) current;
                    CloseableIteration<Statement, QueryEvaluationException> listIter = RyaDAOHelper.query(ryaDAO,
                            listNode, RDF.FIRST, null, conf);
                    try {
                        if (listIter.hasNext()) {
                            final Statement firstStatement = listIter.next();
                            if (firstStatement.getObject() instanceof Resource) {
                                final Resource subclass = (Resource) firstStatement.getObject();
                                final Statement subclassStatement = VF.createStatement(subclass, RDFS.SUBCLASSOF, unionType);
                                addStatementEdge(graph, RDFS.SUBCLASSOF.stringValue(), subclassStatement);
                            }
                        }
                    } finally {
                        listIter.close();
                    }
                    listIter = RyaDAOHelper.query(ryaDAO, listNode, RDF.REST, null, conf);
                    try {
                        if (listIter.hasNext()) {
                            current = listIter.next().getObject();
                        }
                        else {
                            current = RDF.NIL;
                        }
                    } finally {
                        listIter.close();
                    }
                }
            }
        } finally {
            if (iter != null) {
                iter.close();
            }
        }
    }

    private void refreshInverseOf() throws QueryEvaluationException {
        final CloseableIteration<Statement, QueryEvaluationException> iter = RyaDAOHelper.query(ryaDAO, null, OWL.INVERSEOF, null, conf);
        final Map<IRI, IRI> invProp = new HashMap<>();
        try {
            while (iter.hasNext()) {
                final Statement st = iter.next();
                invProp.put((IRI) st.getSubject(), (IRI) st.getObject());
                invProp.put((IRI) st.getObject(), (IRI) st.getSubject());
            }
        } finally {
            if (iter != null) {
                iter.close();
            }
        }
        synchronized(inverseOfMap) {
            inverseOfMap.clear();
            inverseOfMap.putAll(invProp);
        }
    }

    private void refreshPropertyChainPropertyToChain() throws QueryEvaluationException {
        CloseableIteration<Statement, QueryEvaluationException> iter = RyaDAOHelper.query(ryaDAO, null,
                VF.createIRI("http://www.w3.org/2002/07/owl#propertyChainAxiom"),
                null, conf);
        final Map<IRI, IRI> propertyChainPropertiesToBNodes = new HashMap<>();
        final Map<IRI, List<IRI>> tempPropertyChainPropertyToChain = new HashMap<>();
        try {
            while (iter.hasNext()){
                final Statement st = iter.next();
                propertyChainPropertiesToBNodes.put((IRI)st.getSubject(), (IRI)st.getObject());
            }
        } finally {
            if (iter != null) {
                iter.close();
            }
        }
        // now for each property chain bNode, get the indexed list of properties associated with that chain
        for (final IRI propertyChainProperty : propertyChainPropertiesToBNodes.keySet()){
            final IRI bNode = propertyChainPropertiesToBNodes.get(propertyChainProperty);
            // query for the list of indexed properties
            iter = RyaDAOHelper.query(ryaDAO, bNode, VF.createIRI("http://www.w3.org/2000/10/swap/list#index"),
                    null, conf);
            final TreeMap<Integer, IRI> orderedProperties = new TreeMap<>();
            // TODO refactor this.  Wish I could execute sparql
            try {
                while (iter.hasNext()){
                    final Statement st = iter.next();
                    final String indexedElement = st.getObject().stringValue();
                    log.info(indexedElement);
                    CloseableIteration<Statement, QueryEvaluationException>  iter2 = RyaDAOHelper.query(ryaDAO, VF.createIRI(st.getObject().stringValue()), RDF.FIRST,
                            null, conf);
                    String integerValue = "";
                    Value anonPropNode = null;
                    Value propIRI = null;
                    if (iter2 != null){
                        while (iter2.hasNext()){
                            final Statement iter2Statement = iter2.next();
                            integerValue = iter2Statement.getObject().stringValue();
                            break;
                        }
                        iter2.close();
                    }
                    iter2 = RyaDAOHelper.query(ryaDAO, VF.createIRI(st.getObject().stringValue()), RDF.REST,
                            null, conf);
                    if (iter2 != null){
                        while (iter2.hasNext()){
                            final Statement iter2Statement = iter2.next();
                            anonPropNode = iter2Statement.getObject();
                            break;
                        }
                        iter2.close();
                        if (anonPropNode != null){
                            iter2 = RyaDAOHelper.query(ryaDAO, VF.createIRI(anonPropNode.stringValue()), RDF.FIRST,
                                    null, conf);
                            while (iter2.hasNext()){
                                final Statement iter2Statement = iter2.next();
                                propIRI = iter2Statement.getObject();
                                break;
                            }
                            iter2.close();
                        }
                    }
                    if (!integerValue.isEmpty() && propIRI!=null) {
                        try {
                            final int indexValue = Integer.parseInt(integerValue);
                            final IRI chainPropIRI = VF.createIRI(propIRI.stringValue());
                            orderedProperties.put(indexValue, chainPropIRI);
                        }
                        catch (final Exception e){
                            log.error("Error adding chain property to ordered properties", e);
                        }
                    }
                }
            } finally{
                if (iter != null){
                    iter.close();
                }
            }
            final List<IRI> properties = new ArrayList<>();
            for (final Map.Entry<Integer, IRI> entry : orderedProperties.entrySet()){
                properties.add(entry.getValue());
            }
            tempPropertyChainPropertyToChain.put(propertyChainProperty, properties);
        }

        // could also be represented as a list of properties (some of which may be blank nodes)
        for (final IRI propertyChainProperty : propertyChainPropertiesToBNodes.keySet()){
            final List<IRI> existingChain = tempPropertyChainPropertyToChain.get(propertyChainProperty);
            // if we didn't get a chain, try to get it through following the collection
            if ((existingChain == null) || existingChain.isEmpty()) {

                CloseableIteration<Statement, QueryEvaluationException>  iter2 = RyaDAOHelper.query(ryaDAO, propertyChainPropertiesToBNodes.get(propertyChainProperty), RDF.FIRST,
                        null, conf);
                final List<IRI> properties = new ArrayList<>();
                IRI previousBNode = propertyChainPropertiesToBNodes.get(propertyChainProperty);
                if (iter2.hasNext()) {
                    Statement iter2Statement = iter2.next();
                    Value currentPropValue = iter2Statement.getObject();
                    while ((currentPropValue != null) && (!currentPropValue.stringValue().equalsIgnoreCase(RDF.NIL.stringValue()))){
                        if (currentPropValue instanceof IRI){
                            iter2 = RyaDAOHelper.query(ryaDAO, VF.createIRI(currentPropValue.stringValue()), RDF.FIRST,
                                    null, conf);
                            if (iter2.hasNext()){
                                iter2Statement = iter2.next();
                                if (iter2Statement.getObject() instanceof IRI){
                                    properties.add((IRI)iter2Statement.getObject());
                                }
                            }
                            // otherwise see if there is an inverse declaration
                            else {
                                iter2 = RyaDAOHelper.query(ryaDAO, VF.createIRI(currentPropValue.stringValue()), OWL.INVERSEOF,
                                        null, conf);
                                if (iter2.hasNext()){
                                    iter2Statement = iter2.next();
                                    if (iter2Statement.getObject() instanceof IRI){
                                        properties.add(new InverseIRI((IRI)iter2Statement.getObject()));
                                    }
                                }
                            }
                            // get the next prop pointer
                            iter2 = RyaDAOHelper.query(ryaDAO, previousBNode, RDF.REST,
                                    null, conf);
                            if (iter2.hasNext()){
                                iter2Statement = iter2.next();
                                previousBNode = (IRI)currentPropValue;
                                currentPropValue = iter2Statement.getObject();
                            }
                            else {
                                currentPropValue = null;
                            }
                        }
                        else {
                            currentPropValue = null;
                        }

                    }
                    tempPropertyChainPropertyToChain.put(propertyChainProperty, properties);
                }
            }
        }

        synchronized(propertyChainPropertyToChain) {
            propertyChainPropertyToChain.clear();
            propertyChainPropertyToChain.putAll(tempPropertyChainPropertyToChain);
        }
    }

    /**
     * Queries domain and range information, then populates the inference engine with direct
     * domain/range relations and any that can be inferred from the subclass graph, subproperty
     * graph, and inverse property map. Should be called after that class and property information
     * has been refreshed.
     *
     * Computes indirect domain/range:
     *  - If p1 has domain c, and p2 is a subproperty of p1, then p2 also has domain c.
     *  - If p1 has range c, and p2 is a subproperty of p1, then p2 also has range c.
     *  - If p1 has domain c, and p2 is the inverse of p1, then p2 has range c.
     *  - If p1 has range c, and p2 is the inverse of p1, then p2 has domain c.
     *  - If p has domain c1, and c1 is a subclass of c2, then p also has domain c2.
     *  - If p has range c1, and c1 is a subclass of c2, then p also has range c2.
     * @throws QueryEvaluationException
     */
    private void refreshDomainRange() throws QueryEvaluationException {
        final Map<IRI, Set<IRI>> domainByTypePartial = new ConcurrentHashMap<>();
        final Map<IRI, Set<IRI>> rangeByTypePartial = new ConcurrentHashMap<>();
        // First, populate domain and range based on direct domain/range triples.
        CloseableIteration<Statement, QueryEvaluationException> iter = RyaDAOHelper.query(ryaDAO, null, RDFS.DOMAIN, null, conf);
        try {
            while (iter.hasNext()) {
                final Statement st = iter.next();
                final Resource property = st.getSubject();
                final Value domainType = st.getObject();
                if (domainType instanceof IRI && property instanceof IRI) {
                    if (!domainByTypePartial.containsKey(domainType)) {
                        domainByTypePartial.put((IRI) domainType, new HashSet<>());
                    }
                    domainByTypePartial.get(domainType).add((IRI) property);
                }
            }
        } finally {
            if (iter != null) {
                iter.close();
            }
        }
        iter = RyaDAOHelper.query(ryaDAO, null, RDFS.RANGE, null, conf);
        try {
            while (iter.hasNext()) {
                final Statement st = iter.next();
                final Resource property = st.getSubject();
                final Value rangeType = st.getObject();
                if (rangeType instanceof IRI && property instanceof IRI) {
                    if (!rangeByTypePartial.containsKey(rangeType)) {
                        rangeByTypePartial.put((IRI) rangeType, new HashSet<>());
                    }
                    rangeByTypePartial.get(rangeType).add((IRI) property);
                }
            }
        } finally {
            if (iter != null) {
                iter.close();
            }
        }
        // Then combine with the subclass/subproperty graphs and the inverse property map to compute
        // the closure of domain and range per class.
        final Set<IRI> domainRangeTypeSet = new HashSet<>(domainByTypePartial.keySet());
        domainRangeTypeSet.addAll(rangeByTypePartial.keySet());
        // Extend to subproperties: make sure that using a more specific form of a property
        // still triggers its domain/range inferences.
        // Mirror for inverse properties: make sure that using the inverse form of a property
        // triggers the inverse domain/range inferences.
        // These two rules can recursively trigger one another.
        for (final IRI domainRangeType : domainRangeTypeSet) {
            final Set<IRI> propertiesWithDomain = domainByTypePartial.getOrDefault(domainRangeType, new HashSet<>());
            final Set<IRI> propertiesWithRange = rangeByTypePartial.getOrDefault(domainRangeType, new HashSet<>());
            // Since findParents will traverse the subproperty graph and find all indirect
            // subproperties, the subproperty rule does not need to trigger itself directly.
            // And since no more than one inverseOf relationship is stored for any property, the
            // inverse property rule does not need to trigger itself directly. However, each rule
            // can trigger the other, so keep track of how the inferred domains/ranges were
            // discovered so we can apply only those rules that might yield new information.
            final Stack<IRI> domainViaSuperProperty  = new Stack<>();
            final Stack<IRI> rangeViaSuperProperty  = new Stack<>();
            final Stack<IRI> domainViaInverseProperty  = new Stack<>();
            final Stack<IRI> rangeViaInverseProperty  = new Stack<>();
            // Start with the direct domain/range assertions, which can trigger any rule.
            domainViaSuperProperty.addAll(propertiesWithDomain);
            domainViaInverseProperty.addAll(propertiesWithDomain);
            rangeViaSuperProperty.addAll(propertiesWithRange);
            rangeViaInverseProperty.addAll(propertiesWithRange);
            // Repeatedly infer domain/range from subproperties/inverse properties until no new
            // information can be generated.
            while (!(domainViaSuperProperty.isEmpty() && rangeViaSuperProperty.isEmpty()
                    && domainViaInverseProperty.isEmpty() && rangeViaInverseProperty.isEmpty())) {
                // For a type c and property p, if c is a domain of p, then c is the range of any
                // inverse of p. Would be redundant for properties discovered via inverseOf.
                while (!domainViaSuperProperty.isEmpty()) {
                    final IRI property = domainViaSuperProperty.pop();
                    final IRI inverseProperty = findInverseOf(property);
                    if (inverseProperty != null && propertiesWithRange.add(inverseProperty)) {
                        rangeViaInverseProperty.push(inverseProperty);
                    }
                }
                // For a type c and property p, if c is a range of p, then c is the domain of any
                // inverse of p. Would be redundant for properties discovered via inverseOf.
                while (!rangeViaSuperProperty.isEmpty()) {
                    final IRI property = rangeViaSuperProperty.pop();
                    final IRI inverseProperty = findInverseOf(property);
                    if (inverseProperty != null && propertiesWithDomain.add(inverseProperty)) {
                        domainViaInverseProperty.push(inverseProperty);
                    }
                }
                // For a type c and property p, if c is a domain of p, then c is also a domain of
                // p's subproperties. Would be redundant for properties discovered via this rule.
                while (!domainViaInverseProperty.isEmpty()) {
                    final IRI property = domainViaInverseProperty.pop();
                    final Set<IRI> subProperties = getSubProperties(property);
                    subProperties.removeAll(propertiesWithDomain);
                    propertiesWithDomain.addAll(subProperties);
                    domainViaSuperProperty.addAll(subProperties);
                }
                // For a type c and property p, if c is a range of p, then c is also a range of
                // p's subproperties. Would be redundant for properties discovered via this rule.
                while (!rangeViaInverseProperty.isEmpty()) {
                    final IRI property = rangeViaInverseProperty.pop();
                    final Set<IRI> subProperties = getSubProperties(property);
                    subProperties.removeAll(propertiesWithRange);
                    propertiesWithRange.addAll(subProperties);
                    rangeViaSuperProperty.addAll(subProperties);
                }
            }
            if (!propertiesWithDomain.isEmpty()) {
                domainByTypePartial.put(domainRangeType, propertiesWithDomain);
            }
            if (!propertiesWithRange.isEmpty()) {
                rangeByTypePartial.put(domainRangeType, propertiesWithRange);
            }
        }
        // Once all properties have been found for each domain/range class, extend to superclasses:
        // make sure that the consequent of a domain/range inference goes on to apply any more
        // general classes as well.
        for (final IRI subtype : domainRangeTypeSet) {
            final Set<IRI> supertypes = getSuperClasses(subtype);
            final Set<IRI> propertiesWithDomain = domainByTypePartial.getOrDefault(subtype, new HashSet<>());
            final Set<IRI> propertiesWithRange = rangeByTypePartial.getOrDefault(subtype, new HashSet<>());
            for (final IRI supertype : supertypes) {
                // For a property p and its domain c: all of c's superclasses are also domains of p.
                if (!propertiesWithDomain.isEmpty() && !domainByTypePartial.containsKey(supertype)) {
                    domainByTypePartial.put(supertype, new HashSet<>());
                }
                for (final IRI property : propertiesWithDomain) {
                    domainByTypePartial.get(supertype).add(property);
                }
                // For a property p and its range c: all of c's superclasses are also ranges of p.
                if (!propertiesWithRange.isEmpty() && !rangeByTypePartial.containsKey(supertype)) {
                    rangeByTypePartial.put(supertype, new HashSet<>());
                }
                for (final IRI property : propertiesWithRange) {
                    rangeByTypePartial.get(supertype).add(property);
                }
            }
        }
        synchronized(domainByType) {
            domainByType.clear();
            domainByType.putAll(domainByTypePartial);
        }
        synchronized(rangeByType) {
            rangeByType.clear();
            rangeByType.putAll(rangeByTypePartial);
        }
    }

    private void refreshPropertyRestrictions() throws QueryEvaluationException {
        // Get a set of all property restrictions of any type
        final CloseableIteration<Statement, QueryEvaluationException> iter = RyaDAOHelper.query(ryaDAO, null, OWL.ONPROPERTY, null, conf);
        final Map<Resource, IRI> restrictions = new HashMap<>();
        try {
            while (iter.hasNext()) {
                final Statement st = iter.next();
                restrictions.put(st.getSubject(), (IRI) st.getObject());
            }
        } finally {
            if (iter != null) {
                iter.close();
            }
        }
        // Query for specific types of restriction and add their details to the schema
        refreshHasValueRestrictions(restrictions);
        refreshSomeValuesFromRestrictions(restrictions);
        refreshAllValuesFromRestrictions(restrictions);
        refreshHasSelfRestrictions(restrictions);
    }

    private void refreshHasValueRestrictions(final Map<Resource, IRI> restrictions) throws QueryEvaluationException {
        hasValueByType.clear();
        hasValueByProperty.clear();
        final CloseableIteration<Statement, QueryEvaluationException> iter = RyaDAOHelper.query(ryaDAO, null, OWL.HASVALUE, null, conf);
        try {
            while (iter.hasNext()) {
                final Statement st = iter.next();
                final Resource restrictionClass = st.getSubject();
                if (restrictions.containsKey(restrictionClass)) {
                    final IRI property = restrictions.get(restrictionClass);
                    final Value value = st.getObject();
                    if (!hasValueByType.containsKey(restrictionClass)) {
                        hasValueByType.put(restrictionClass, new HashMap<>());
                    }
                    if (!hasValueByProperty.containsKey(property)) {
                        hasValueByProperty.put(property, new HashMap<>());
                    }
                    hasValueByType.get(restrictionClass).put(property, value);
                    hasValueByProperty.get(property).put(restrictionClass, value);
                }
            }
        } finally {
            if (iter != null) {
                iter.close();
            }
        }
    }

    private void refreshSomeValuesFromRestrictions(final Map<Resource, IRI> restrictions) throws QueryEvaluationException {
        someValuesFromByRestrictionType.clear();
        ryaDaoQueryWrapper.queryAll(null, OWL.SOMEVALUESFROM, null, new AbstractRDFHandler() {
            @Override
            public void handleStatement(final Statement statement) throws RDFHandlerException {
                final Resource restrictionClass = statement.getSubject();
                if (restrictions.containsKey(restrictionClass) && statement.getObject() instanceof Resource) {
                    final IRI property = restrictions.get(restrictionClass);
                    final Resource valueClass = (Resource) statement.getObject();
                    // Should also be triggered by subclasses of the value class
                    final Set<Resource> valueClasses = new HashSet<>();
                    valueClasses.add(valueClass);
                    if (valueClass instanceof IRI) {
                        valueClasses.addAll(getSubClasses((IRI) valueClass));
                    }
                    for (final Resource valueSubClass : valueClasses) {
                        if (!someValuesFromByRestrictionType.containsKey(restrictionClass)) {
                            someValuesFromByRestrictionType.put(restrictionClass, new ConcurrentHashMap<>());
                        }
                        someValuesFromByRestrictionType.get(restrictionClass).put(valueSubClass, property);
                    }
                }
            }
        });
    }

    private void refreshAllValuesFromRestrictions(final Map<Resource, IRI> restrictions) throws QueryEvaluationException {
        allValuesFromByValueType.clear();
        ryaDaoQueryWrapper.queryAll(null, OWL.ALLVALUESFROM, null, new AbstractRDFHandler() {
            @Override
            public void handleStatement(final Statement statement) throws RDFHandlerException {
                final Resource directRestrictionClass = statement.getSubject();
                if (restrictions.containsKey(directRestrictionClass) && statement.getObject() instanceof Resource) {
                    final IRI property = restrictions.get(directRestrictionClass);
                    final Resource valueClass = (Resource) statement.getObject();
                    // Should also be triggered by subclasses of the property restriction
                    final Set<Resource> restrictionClasses = new HashSet<>();
                    restrictionClasses.add(directRestrictionClass);
                    if (directRestrictionClass instanceof IRI) {
                        restrictionClasses.addAll(getSubClasses((IRI) directRestrictionClass));
                    }
                    for (final Resource restrictionClass : restrictionClasses) {
                        if (!allValuesFromByValueType.containsKey(valueClass)) {
                            allValuesFromByValueType.put(valueClass, new ConcurrentHashMap<>());
                        }
                        allValuesFromByValueType.get(valueClass).put(restrictionClass, property);
                    }
                }
            }
        });
    }

    private void refreshHasSelfRestrictions(final Map<Resource, IRI> restrictions) throws QueryEvaluationException {
        hasSelfByType.clear();
        hasSelfByProperty.clear();

        for(final Resource type : restrictions.keySet()) {
            final IRI property = restrictions.get(type);
            final CloseableIteration<Statement, QueryEvaluationException> iter = RyaDAOHelper.query(ryaDAO, type, HAS_SELF, null, conf);
            try {
                if (iter.hasNext()) {
                    Set<IRI> typeSet = hasSelfByType.get(type);
                    Set<Resource> propSet = hasSelfByProperty.get(property);

                    if (typeSet == null) {
                        typeSet = new HashSet<>();
                    }
                    if (propSet == null) {
                        propSet = new HashSet<>();
                    }

                    typeSet.add(property);
                    propSet.add(type);

                    hasSelfByType.put(type, typeSet);
                    hasSelfByProperty.put(property, propSet);
                }
            } finally {
                if (iter != null) {
                    iter.close();
                }
            }
        }
    }

    private void refreshIntersectionOf() throws QueryEvaluationException {
        final Map<Resource, List<Set<Resource>>> intersectionsProp = new HashMap<>();

        // First query for all the owl:intersectionOf's.
        // If we have the following intersectionOf:
        // :A owl:intersectionOf[:B, :C]
        // It will be represented by triples following a pattern similar to:
        // <:A> owl:intersectionOf _:bnode1 .
        //  _:bnode1 rdf:first <:B> .
        //  _:bnode1 rdf:rest _:bnode2 .
        // _:bnode2 rdf:first <:C> .
        // _:bnode2 rdf:rest rdf:nil .
        ryaDaoQueryWrapper.queryAll(null, OWL.INTERSECTIONOF, null, new AbstractRDFHandler() {
            @Override
            public void handleStatement(final Statement statement) throws RDFHandlerException {
                final Resource type = statement.getSubject();
                // head will point to a type that is part of the intersection.
                final IRI head = (IRI) statement.getObject();
                if (!intersectionsProp.containsKey(type)) {
                    intersectionsProp.put(type, new ArrayList<Set<Resource>>());
                }

                // head should point to a list of items that forms the
                // intersection.
                try {
                    final Set<Resource> intersection = new LinkedHashSet<>(getList(head));
                    if (!intersection.isEmpty()) {
                        // Add this intersection for this type. There may be more
                        // intersections for this type so each type has a list of
                        // intersection sets.
                        intersectionsProp.get(type).add(intersection);
                    }
                } catch (final QueryEvaluationException e) {
                    throw new RDFHandlerException("Error getting intersection list.", e);
                }
            }
        });

        intersections.clear();
        for (final Entry<Resource, List<Set<Resource>>> entry : intersectionsProp.entrySet()) {
            final Resource type = entry.getKey();
            final List<Set<Resource>> intersectionList = entry.getValue();
            final Set<Resource> otherTypes = new HashSet<>();
            // Combine all of a type's intersections together.
            for (final Set<Resource> intersection : intersectionList) {
                otherTypes.addAll(intersection);
            }
            for (final Resource other : otherTypes) {
                // :A intersectionOf[:B, :C] implies that
                // :A subclassOf :B
                // :A subclassOf :C
                // So add each type that's part of the intersection to the
                // subClassOf graph.
                addSubClassOf(type, other);
                for (final Set<Resource> intersection : intersectionList) {
                    if (!intersection.contains(other)) {
                        addIntersection(intersection, other);
                    }
                }
            }
            for (final Set<Resource> intersection : intersectionList) {
                addIntersection(intersection, type);
            }
        }
        for (final Entry<Resource, List<Set<Resource>>> entry : intersectionsProp.entrySet()) {
            final Resource type = entry.getKey();
            final List<Set<Resource>> intersectionList = entry.getValue();

            final Set<IRI> superClasses = getSuperClasses((IRI) type);
            for (final IRI superClass : superClasses) {
                // Add intersections to super classes if applicable.
                // IF:
                // :A intersectionOf[:B, :C]
                // AND
                // :A subclassOf :D
                // Then we can infer:
                // intersectionOf[:B, :C] subclassOf :D
                for (final Set<Resource> intersection : intersectionList) {
                    addIntersection(intersection, superClass);
                }
            }
            // Check if other keys have any of the same intersections and infer
            // the same subclass logic to them that we know from the current
            // type. Propagating up through all the superclasses.
            for (final Set<Resource> intersection : intersectionList) {
                final Set<Resource> otherKeys = Sets.newHashSet(intersectionsProp.keySet());
                otherKeys.remove(type);
                for (final Resource otherKey : otherKeys) {
                    if (intersectionsProp.get(otherKey).contains(intersection)) {
                        addSubClassOf(otherKey, type);
                        addSubClassOf(type, otherKey);
                    }
                }
            }
        }
    }

    private void refreshOneOf() throws QueryEvaluationException {
        final Map<Resource, Set<Resource>> enumTypes = new HashMap<>();

        // First query for all the owl:oneOf's.
        // If we have the following oneOf:
        // :A owl:oneOf (:B, :C)
        // It will be represented by triples following a pattern similar to:
        // <:A> owl:oneOf _:bnode1 .
        //  _:bnode1 rdf:first <:B> .
        //  _:bnode1 rdf:rest _:bnode2 .
        // _:bnode2 rdf:first <:C> .
        // _:bnode2 rdf:rest rdf:nil .
        ryaDaoQueryWrapper.queryAll(null, OWL.ONEOF, null, new AbstractRDFHandler() {
            @Override
            public void handleStatement(final Statement statement) throws RDFHandlerException {
                final Resource enumType = statement.getSubject();
                // listHead will point to a type class of the enumeration.
                final IRI listHead = (IRI) statement.getObject();
                if (!enumTypes.containsKey(enumType)) {
                    enumTypes.put(enumType, new LinkedHashSet<Resource>());
                }

                // listHead should point to a list of items that forms the
                // enumeration.
                try {
                    final Set<Resource> enumeration = new LinkedHashSet<>(getList(listHead));
                    if (!enumeration.isEmpty()) {
                        // Add this enumeration for this type.
                        enumTypes.get(enumType).addAll(enumeration);
                    }
                } catch (final QueryEvaluationException e) {
                    throw new RDFHandlerException("Error getting enumeration list.", e);
                }
            }
        });

        synchronized(enumerations) {
            enumerations.clear();
            enumerations.putAll(enumTypes);
        }
    }

    /**
     * For a given type, return any properties such that some owl:hasSelf
     * restrictions implies that properties of this type have the value of
     * themselves for this type.
     *
     * This takes into account type hierarchy, where children of a type that
     * have this property are also assumed to have the property.
     *
     * @param type
     *            The type (IRI or bnode) to check against the known
     *            restrictions
     * @return For each relevant property, a set of values such that whenever a
     *         resource has that value for that property, it is implied to
     *         belong to the type.
     */
    public Set<IRI> getHasSelfImplyingType(final Resource type){
        // return properties that imply this type if reflexive
        final Set<IRI> properties = new HashSet<>();
        Set<IRI> tempProperties = hasSelfByType.get(type);

        if (tempProperties != null) {
            properties.addAll(tempProperties);
        }
        //findParent gets all subclasses, add self.
        if (type instanceof IRI) {
            for (final IRI subtype : findParents(subClassOfGraph.get(), (IRI) type)) {
                tempProperties = hasSelfByType.get(subtype);
                if (tempProperties != null) {
                    properties.addAll(tempProperties);
                }
            }
        }

        // make map hasSelfByType[]
        return properties;
    }

    /**
     * For a given property, return any types such that some owl:hasSelf restriction implies that members
     * of the type have the value of themselves for this property.
     *
     * This takes into account type hierarchy, where children of a type that have
     * this property are also assumed to have the property.
     * @param property The property whose owl:hasSelf restrictions to return
     * @return A set of types that possess the implied property.
     */
    public Set<Resource> getHasSelfImplyingProperty(final IRI property) {
        // return types that imply this type if reflexive
        final Set<Resource> types = new HashSet<>();
        final Set<Resource> baseTypes = hasSelfByProperty.get(property);

        if (baseTypes != null) {
            types.addAll(baseTypes);
            // findParent gets all subclasses, add self.
            for (final Resource baseType : baseTypes) {
                if (baseType instanceof IRI) {
                    types.addAll(findParents(subClassOfGraph.get(), (IRI) baseType));
                }
            }
        }

        // make map hasSelfByProperty[]
        return types;
    }

    /**
     * Queries for all items that are in a list of the form:
     * <pre>
     *     <:A> ?x _:bnode1 .
     *     _:bnode1 rdf:first <:B> .
     *     _:bnode1 rdf:rest _:bnode2 .
     *     _:bnode2 rdf:first <:C> .
     *     _:bnode2 rdf:rest rdf:nil .
     * </pre>
     * Where {@code :_bnode1} represents the first item in the list and
     * {@code ?x} is some restriction on {@code <:A>}. This will return the
     * list of resources, {@code [<:B>, <:C>]}.
     * @param firstItem the first item in the list.
     * @return the {@link List} of {@link Resource}s.
     * @throws QueryEvaluationException
     */
    private List<Resource> getList(final IRI firstItem) throws QueryEvaluationException {
        IRI head = firstItem;
        final List<Resource> list = new ArrayList<>();
        // Go through and find all bnodes that are part of the defined list.
        while (!RDF.NIL.equals(head)) {
            // rdf.first will point to a type item that is in the list.
            ryaDaoQueryWrapper.queryFirst(head, RDF.FIRST, null, new AbstractRDFHandler() {
                @Override
                public void handleStatement(final Statement statement) throws RDFHandlerException {
                    // The object found in the query represents a type
                    // that should be included in the list.
                    final IRI object = (IRI) statement.getObject();
                    list.add(object);
                }
            });
            final MutableObject<IRI> headHolder = new MutableObject<>();
            // rdf.rest will point to the next bnode that's part of the list.
            ryaDaoQueryWrapper.queryFirst(head, RDF.REST, null, new AbstractRDFHandler() {
                @Override
                public void handleStatement(final Statement statement) throws RDFHandlerException {
                    // This object is the next bnode head to look for.
                    final IRI object = (IRI) statement.getObject();
                    headHolder.setValue(object);
                }
            });
            // As long as we get a new head there are more bnodes that are part
            // of the list. Keep going until we reach rdf.nil.
            if (headHolder.getValue() != null) {
                head = headHolder.getValue();
            } else {
                head = RDF.NIL;
            }
        }
        return list;
    }

    private void addSubClassOf(final Resource s, final Resource o) {
        final Statement statement = VF.createStatement(s, RDFS.SUBCLASSOF, o);
        final String edgeName = RDFS.SUBCLASSOF.stringValue();

        addStatementEdge(subClassOfGraph.get(), edgeName, statement);
    }

    private void addIntersection(final Set<Resource> intersection, final Resource type) {
        if (type != null && intersection != null && !intersection.isEmpty()) {
            List<Set<Resource>> intersectionList = intersections.get(type);
            if (intersectionList == null) {
                intersectionList = new ArrayList<>();
            }
            if (!intersectionList.contains(intersection)) {
                intersectionList.add(intersection);
            }
            intersections.put(type, intersectionList);
        }
    }

    private static Vertex getVertex(final Graph graph, final Object id) {
        final Iterator<Vertex> it = graph.vertices(id.toString());
        if (it.hasNext()) {
            return it.next();
        }
        return null;
    }

    private static void addStatementEdge(final Graph graph, final String edgeName, final Statement st) {
        final Resource subj = st.getSubject();
        Vertex a = getVertex(graph, subj);
        if (a == null) {
            a = graph.addVertex(T.id, subj.toString());
            a.property(URI_PROP, subj);
        }
        final Value obj = st.getObject();
        Vertex b = getVertex(graph, obj);
        if (b == null) {
            b = graph.addVertex(T.id, obj.toString());
            b.property(URI_PROP, obj);
        }
        a.addEdge(edgeName, b);
    }

    /**
     * Returns all super class types of the specified type based on the
     * internal subclass graph.
     * @param type the type {@link IRI} to find super classes for.
     * @return the {@link Set} of {@link IRI} types that are super classes types
     * of the specified {@code type}. Returns an empty set if nothing was found,
     * or if either type or the subclass graph is {@code null}.
     */
    public Set<IRI> getSuperClasses(final IRI type) {
        return findChildren(subClassOfGraph.get(), type);
    }

    /**
     * Returns all sub class types of the specified type based on the
     * internal subclass graph.
     * @param type the type {@link IRI} to find sub classes for.
     * @return the {@link Set} of {@link IRI} types that are sub classes types
     * of the specified {@code type}. Returns an empty set if nothing was found,
     * or if either type or the subclass graph is {@code null}.
     */
    public Set<IRI> getSubClasses(final IRI type) {
        return findParents(subClassOfGraph.get(), type);
    }

    /**
     * Returns all superproperties of the specified property based on the
     * internal subproperty graph.
     * @param property the property {@link IRI} to find superproperties for.
     * @return the {@link Set} of {@link IRI} properties that are superproperties
     * of the specified {@code property}. Returns an empty set if nothing was found,
     * or if either property or the subproperty graph is {@code null}.
     */
    public Set<IRI> getSuperProperties(final IRI property) {
        return findChildren(subPropertyOfGraph.get(), property);
    }

    /**
     * Returns all subproperties of the specified property based on the
     * internal subproperty graph.
     * @param property the property {@link IRI} to find subproperties for.
     * @return the {@link Set} of {@link IRI} properties that are subproperties
     * of the specified {@code property}. Returns an empty set if nothing was found,
     * or if either property or the subproperty graph is {@code null}.
     */
    public Set<IRI> getSubProperties(final IRI property) {
        return findParents(subPropertyOfGraph.get(), property);
    }

    /**
     * Given a graph and a node, recursively traverse the graph from that node
     * to find all predecessors.
     * @param graph A {@link Graph}
     * @param vertexId The starting node
     * @return The set of predecessors, or an empty set if none are found or if
     *      either argument is {@code null}
     */
    public static Set<IRI> findParents(final Graph graph, final IRI vertexId) {
        return findParents(graph, vertexId, true);
    }

    /**
     * Given a graph and a node, find all immediate parents and optionally
     * traverse the graph recursively to find all indirect predecessors.
     * @param graph A {@link Graph}
     * @param vertexId The starting node
     * @param isRecursive If true, traverse the graph recursively
     * @return The set of predecessors, or an empty set if none are found or if
     *      either argument is {@code null}
     */
    public static Set<IRI> findParents(final Graph graph, final IRI vertexId, final boolean isRecursive) {
        return findConnected(graph, vertexId, Direction.IN, isRecursive);
    }

    /**
     * Given a graph and a node, recursively traverse the graph from that node
     * to find all successors.
     * @param graph A {@link Graph}
     * @param vertexId The starting node
     * @return The set of successors, or an empty set if none are found or if
     *      either argument is {@code null}
     */
    public static Set<IRI> findChildren(final Graph graph, final IRI vertexId) {
        return findChildren(graph, vertexId, true);
    }

    /**
     * Given a graph and a node, find all immediate children and optionally
     * traverse the graph recursively to find all indirect successors.
     * @param graph A {@link Graph}
     * @param vertexId The starting node
     * @param isRecursive If true, traverse the graph recursively
     * @return The set of successors, or an empty set if none are found or if
     *      either argument is {@code null}
     */
    public static Set<IRI> findChildren(final Graph graph, final IRI vertexId, final boolean isRecursive) {
        return findConnected(graph, vertexId, Direction.OUT, isRecursive);
    }

    /**
     * Given a graph, a starting node, and a direction, find immediate neighbors
     * of the start node in that direction, and optionally traverse the graph
     * recursively in that same direction to find indirect connections.
     * @param graph A {@link Graph}
     * @param vertexId The starting node
     * @param traversal Look for connected nodes in this direction
     * @param isRecursive If true, recursively follow the connected nodes' own
     *      edges (in the same direction)
     * @return The set of connected nodes, or an empty set if none are found, or
     *      if either the graph or the starting vertex are {@code null}.
     */
    private static Set<IRI> findConnected(final Graph graph, final IRI vertexId, final Direction traversal, final boolean isRecursive) {
        final Set<IRI> connected = new HashSet<>();
        if (graph == null || vertexId == null) {
            return connected;
        }
        final Vertex v = getVertex(graph, vertexId);
        if (v == null) {
            return connected;
        }
        addConnected(v, connected, traversal, isRecursive);
        return connected;
    }

    private static void addConnected(final Vertex v, final Set<IRI> connected, final Direction traversal, final boolean isRecursive) {
        v.edges(traversal).forEachRemaining(edge -> {
            final Vertex ov = edge.vertices(traversal.opposite()).next();
            final Object o = ov.property(URI_PROP).value();
            if (o != null && o instanceof IRI) {
                final boolean contains = connected.contains(o);
                if (!contains) {
                    connected.add((IRI) o);
                    if (isRecursive) {
                        addConnected(ov, connected, traversal, isRecursive);
                    }
                }
            }
        });
    }

    public boolean isSymmetricProperty(final IRI prop) {
        return (symmetricPropertySet != null) && symmetricPropertySet.contains(prop);
    }

    public IRI findInverseOf(final IRI prop) {
        return (inverseOfMap != null) ? inverseOfMap.get(prop) : (null);
    }

    public boolean isTransitiveProperty(final IRI prop) {
        return (transitivePropertySet != null) && transitivePropertySet.contains(prop);
    }

    /**
     * Return whether a given property is known to be reflexive.
     * @param prop A IRI
     * @return True if the given IRI corresponds to an owl:ReflexiveProperty
     */
    public boolean isReflexiveProperty(final IRI prop) {
        return (reflexivePropertySet != null) && reflexivePropertySet.contains(prop);
    }

    /**
     * TODO: This chaining can be slow at query execution. the other option is to perform this in the query itself, but that will be constrained to how many levels we decide to go
     */
    public Set<Statement> findTransitiveProperty(final Resource subj, final IRI prop, final Value obj, final Resource... contxts) throws InferenceEngineException {
        if (transitivePropertySet.contains(prop)) {
            final Set<Statement> sts = new HashSet<>();
            final boolean goUp = subj == null;
            chainTransitiveProperty(subj, prop, obj, (goUp) ? (obj) : (subj), sts, goUp, contxts);
            return sts;
        } else {
            return null;
        }
    }

    /**
     * TODO: This chaining can be slow at query execution. the other option is to perform this in the query itself, but that will be constrained to how many levels we decide to go
     */
    public Set<Resource> findSameAs(final Resource value, final Resource... contxts) throws InferenceEngineException{
        final Set<Resource> sameAs = new HashSet<>();
        sameAs.add(value);
        findSameAsChaining(value, sameAs, contxts);
        return sameAs;
    }

    public CloseableIteration<Statement, QueryEvaluationException> queryDao(final Resource subject, final IRI predicate, final Value object, final Resource... contexts) throws QueryEvaluationException {
        return RyaDAOHelper.query(ryaDAO, subject, predicate, object, conf, contexts);
    }

    /**
     * TODO: This chaining can be slow at query execution. the other option is to perform this in the query itself, but that will be constrained to how many levels we decide to go
     */
    public void findSameAsChaining(final Resource subj, final Set<Resource> currentSameAs, final Resource[] contxts) throws InferenceEngineException{
        CloseableIteration<Statement, QueryEvaluationException> subjIter = null;
        CloseableIteration<Statement, QueryEvaluationException> objIter = null;
        try {
            subjIter = queryDao(subj, OWL.SAMEAS, null, contxts);
            while (subjIter.hasNext()){
                final Statement st = subjIter.next();
                if (!currentSameAs.contains(st.getObject())){
                    final Resource castedObj = (Resource) st.getObject();
                    currentSameAs.add(castedObj);
                    findSameAsChaining(castedObj, currentSameAs, contxts);
                }
            }
            objIter = queryDao(null, OWL.SAMEAS, subj, contxts);
            while (objIter.hasNext()){
                final Statement st = objIter.next();
                if (!currentSameAs.contains(st.getSubject())){
                    final Resource sameAsSubj = st.getSubject();
                    currentSameAs.add(sameAsSubj);
                    findSameAsChaining(sameAsSubj, currentSameAs, contxts);
                }
            }
        } catch (final QueryEvaluationException e) {
            throw new InferenceEngineException(e);
        } finally {
            if (subjIter != null) {
                try {
                    subjIter.close();
                } catch (final QueryEvaluationException e) {
                    throw new InferenceEngineException("Error while closing \"same as chaining\" statement subject iterator.", e);
                }
            }
            if (objIter != null) {
                try {
                    objIter.close();
                } catch (final QueryEvaluationException e) {
                    throw new InferenceEngineException("Error while closing \"same as chaining\" statement object iterator.", e);
                }
            }
        }
    }

    protected void chainTransitiveProperty(final Resource subj, final IRI prop, final Value obj, final Value core, final Set<Statement> sts, final boolean goUp, final Resource[] contxts) throws InferenceEngineException {
        CloseableIteration<Statement, QueryEvaluationException> iter = null;
        try {
            iter = queryDao(subj, prop, obj, contxts);
            while (iter.hasNext()) {
                final Statement st = iter.next();
                sts.add(VF.createStatement((goUp) ? (st.getSubject()) : (Resource) (core), prop, (!goUp) ? (st.getObject()) : (core)));
                if (goUp) {
                    chainTransitiveProperty(null, prop, st.getSubject(), core, sts, goUp, contxts);
                } else {
                    chainTransitiveProperty((Resource) st.getObject(), prop, null, core, sts, goUp, contxts);
                }
            }
        } catch (final QueryEvaluationException e) {
            throw new InferenceEngineException(e);
        } finally {
            if (iter != null) {
                try {
                    iter.close();
                } catch (final QueryEvaluationException e) {
                    throw new InferenceEngineException("Error while closing \"chain transitive\" property statement iterator.", e);
                }
            }
        }
    }

    public boolean isInitialized() {
        return isInitialized.get();
    }

    public void setInitialized(final boolean isInitialized) {
        this.isInitialized.set(isInitialized);
    }

    public synchronized RyaDAO<?> getRyaDAO() {
        return ryaDAO;
    }

    public synchronized void setRyaDAO(final RyaDAO<?> ryaDAO) {
        this.ryaDAO = ryaDAO;
        ryaDaoQueryWrapper = new RyaDaoQueryWrapper(ryaDAO);
    }

    public synchronized RdfCloudTripleStoreConfiguration getConf() {
        return conf;
    }

    public synchronized void setConf(final RdfCloudTripleStoreConfiguration conf) {
        this.conf = conf;
    }

    public Graph getSubClassOfGraph() {
        return subClassOfGraph.get();
    }

    public Map<IRI, List<IRI>> getPropertyChainMap() {
        return propertyChainPropertyToChain;
    }

    public List<IRI> getPropertyChain(final IRI chainProp) {
        if (propertyChainPropertyToChain.containsKey(chainProp)){
            return propertyChainPropertyToChain.get(chainProp);
        }
        return new ArrayList<IRI>();
    }

    public Graph getSubPropertyOfGraph() {
        return subPropertyOfGraph.get();
    }

    public long getRefreshGraphSchedule() {
        return refreshGraphSchedule.get();
    }

    public void setRefreshGraphSchedule(final long refreshGraphSchedule) {
        this.refreshGraphSchedule.set(refreshGraphSchedule);
    }

    public Set<IRI> getSymmetricPropertySet() {
        return symmetricPropertySet;
    }

    public Map<IRI, IRI> getInverseOfMap() {
        return inverseOfMap;
    }

    public Set<IRI> getTransitivePropertySet() {
        return transitivePropertySet;
    }

    public boolean isSchedule() {
        return schedule.get();
    }

    public void setSchedule(final boolean schedule) {
        this.schedule.set(schedule);
    }

    /**
     * For a given type, return any properties and values such that owl:hasValue restrictions on
     * those properties could imply this type. No matter how many restrictions are returned, each
     * one is considered individually sufficient: if a resource has the property and the value, then
     * it belongs to the provided type. Takes type hierarchy into account, so the value may imply a
     * subtype which in turn implies the provided type.
     * @param type The type (IRI or bnode) to check against the known restrictions
     * @return For each relevant property, a set of values such that whenever a resource has that
     *      value for that property, it is implied to belong to the type.
     */
    public Map<IRI, Set<Value>> getHasValueByType(final Resource type) {
        final Map<IRI, Set<Value>> implications = new HashMap<>();
        if (hasValueByType != null) {
            final Set<Resource> types = new HashSet<>();
            types.add(type);
            if (type instanceof IRI) {
                types.addAll(getSubClasses((IRI) type));
            }
            for (final Resource relevantType : types) {
                if (hasValueByType.containsKey(relevantType)) {
                    for (final Map.Entry<IRI, Value> propertyToValue : hasValueByType.get(relevantType).entrySet()) {
                        if (!implications.containsKey(propertyToValue.getKey())) {
                            implications.put(propertyToValue.getKey(), new HashSet<>());
                        }
                        implications.get(propertyToValue.getKey()).add(propertyToValue.getValue());
                    }
                }
            }
        }
        return implications;
    }

    /**
     * For a given property, return any types and values such that some owl:hasValue restriction
     * states that members of the type are implied to have the associated specific value(s) for
     * this property. Takes class hierarchy into account, which means one type may imply multiple
     * values by way of supertypes with their own restrictions. Does not consider the property
     * hierarchy, so only restrictions that directly reference the given property (using
     * owl:onProperty) are relevant.
     * @param property The property whose owl:hasValue restrictions to return
     * @return A mapping from type (URIs or bnodes) to the set of any values that belonging to that
     *      type implies.
     */
    public Map<Resource, Set<Value>> getHasValueByProperty(final IRI property) {
        final Map<Resource, Set<Value>> implications = new HashMap<>();
        if (hasValueByProperty != null && hasValueByProperty.containsKey(property)) {
            for (final Map.Entry<Resource, Value> typeToValue : hasValueByProperty.get(property).entrySet()) {
                final Resource type = typeToValue.getKey();
                if (!implications.containsKey(type)) {
                    implications.put(type, new HashSet<>());
                }
                implications.get(type).add(typeToValue.getValue());
                if (type instanceof IRI) {
                    for (final IRI subtype : getSubClasses((IRI) type)) {
                        if (!implications.containsKey(subtype)) {
                            implications.put(subtype, new HashSet<>());
                        }
                        implications.get(subtype).add(typeToValue.getValue());
                    }
                }
            }
        }
        return implications;
    }

    /**
     * For a given type, get all properties which have that type as a domain. That type can be
     * inferred for any resource which is a subject of any triple involving one of these properties.
     * Accounts for class and property hierarchy, for example that a subproperty implicitly has its
     * superproperty's domain, as well as inverse properties, where a property's range is its
     * inverse property's domain.
     * @param domainType The type to check against the known domains
     * @return The set of properties with domain of that type, meaning that any triple whose
     *      predicate belongs to that set implies that the triple's subject belongs to the type.
     */
    public Set<IRI> getPropertiesWithDomain(final IRI domainType) {
        final Set<IRI> properties = new HashSet<>();
        if (domainByType.containsKey(domainType)) {
            properties.addAll(domainByType.get(domainType));
        }
        return properties;
    }

    /**
     * For a given type, get all properties which have that type as a range. That type can be
     * inferred for any resource which is an object of any triple involving one of these properties.
     * Accounts for class and property hierarchy, for example that a subproperty implicitly has its
     * superproperty's range, as well as inverse properties, where a property's domain is its
     * inverse property's range.
     * @param rangeType The type to check against the known ranges
     * @return The set of properties with range of that type, meaning that any triple whose
     *      predicate belongs to that set implies that the triple's object belongs to the type.
     */
    public Set<IRI> getPropertiesWithRange(final IRI rangeType) {
        final Set<IRI> properties = new HashSet<>();
        if (rangeByType.containsKey(rangeType)) {
            properties.addAll(rangeByType.get(rangeType));
        }
        return properties;
    }

    /**
     * Given some schema mapping types to (type, property) pairs that somehow imply the key type,
     * and given a particular type being queried for, expand the combinations of types and
     * properties that can imply the query type by including any pairs that could imply subtypes of
     * the query type (using the subclass graph), and by expanding each property into a set of all
     * subproperties that imply it (using the subproperty graph). Does not consider subtypes of
     * potential triggering types.
     * @param queryType The type whose possible derivations are needed
     * @param schemaMap Map of schema information such that each key represents a type that can
     *      somehow be derived from (other type x property) combinations, and the value provides
     *      those combinations that can be used for the implication.
     * @return Combinations of types and properties that can directly or indirectly imply the query
     *      type according to the schema provided and the subclass/superproperty graphs. Any
     *      individual type/property combination is sufficient. Returns an empty map if either
     *      parameter is {@code null}.
     */
    private Map<Resource, Set<IRI>> getTypePropertyImplyingType(final Resource queryType, final Map<Resource, Map<Resource, IRI>> schemaMap) {
        final Map<Resource, Set<IRI>> implications = new HashMap<>();
        if (schemaMap != null && queryType != null) {
            // Check for any subtypes which would in turn imply the type being queried for
            final HashSet<Resource> queryTypes = new HashSet<>();
            queryTypes.add(queryType);
            if (queryType instanceof IRI) {
                queryTypes.addAll(getSubClasses((IRI) queryType));
            }
            for (final Resource querySubType : queryTypes) {
                if (schemaMap.containsKey(querySubType)) {
                    final Map<Resource, IRI> otherTypeToProperty = schemaMap.get(querySubType);
                    for (final Resource otherType : otherTypeToProperty.keySet()) {
                        if (!implications.containsKey(otherType)) {
                            implications.put(otherType, new HashSet<>());
                        }
                        final IRI property = otherTypeToProperty.get(otherType);
                        if (property != null) {
                            implications.get(otherType).add(property);
                            // Also add subproperties that would in turn imply the property
                            implications.get(otherType).addAll(getSubProperties(property));
                        }
                    }
                }
            }
        }
        return implications;
    }

    /**
     * For a given type, return information about any owl:someValuesFrom restriction that could
     * imply an individual's membership in that type: When a property restriction R applies to
     * property p and states "R owl:someValuesFrom T", then whenever the object of a triple belongs
     * to T, and the predicate is p, then the subject of the triple is implied to have the type R
     * (it belongs to the class defined by the restriction).
     * @param restrictionType The type to be inferred, which is the type of the subject of the
     *      triple, or the type for which all members are stated to have some value of the
     *      appropriate type. Takes class hierarchy into account, so possible inferences include
     *      any ways of inferring subtypes of the restriction type, and object types that trigger
     *      inference include any subtypes of relevant value types. Also considers property
     *      hierarchy, so properties that trigger inference will include subproperties of those
     *      referenced by relevant restrictions.
     * @return A map from object type (the object of the someValuesFrom condition or the subtype of
     *      such a type) to the set of properties (including any property referenced by such a
     *      restriction and all of its subproperties) such that for any individual which belongs to
     *      the object type, any subject which has some value of that type for that property belongs
     *      to the restriction type. Empty map if the parameter is {@code null} or if the
     *      someValuesFrom schema has not been populated.
     */
    public Map<Resource, Set<IRI>> getSomeValuesFromByRestrictionType(final Resource restrictionType) {
        return getTypePropertyImplyingType(restrictionType, someValuesFromByRestrictionType);
    }

    /**
     * For a given type, return information about any owl:allValuesFrom restriction that could imply
     * an individual's membership in that type: If the subject of a triple belongs to the type
     * associated with the restriction itself, and the predicate is the one referenced by the
     * restriction, then the object of the triple is implied to have the value type.
     * @param valueType The type to be inferred, which is the type of the object of the triple, or
     *      the type from which all values are stated to belong. Takes class hierarchy into account,
     *      so possible inferences include any ways of inferring subtypes of the value type, and
     *      subject types that trigger inference include any subtypes of relevant restrictions.
     *      Also considers property hierarchy, so properties that trigger inference will include
     *      subproperties of those referenced by relevant restrictions.
     * @return A map from subject type (a property restriction type or a subtype of one) to the set
     *      of properties (including any property referenced by such a restriction and all of its
     *      subproperties) such that for any individual which belongs to the subject type, all
     *      values it has for any of those properties belong to the value type. Empty map if the
     *      parameter is {@code null} or if the allValuesFrom schema has not been populated.
     */
    public Map<Resource, Set<IRI>> getAllValuesFromByValueType(final Resource valueType) {
        return getTypePropertyImplyingType(valueType, allValuesFromByValueType);
    }

    /**
     * For a given type, return all sets of types such that owl:intersectionOf
     * restrictions on those properties could imply this type.  A type can have
     * multiple intersections and each intersection is a set of types so a list
     * of all the type sets is returned.
     * @param type The type (IRI or bnode) to check against the known
     * intersections.
     * @return A {@link List} of {@link Resource} type {@link Set}s that
     * represents all the known intersections that imply the specified type.
     * {@code null} is returned if no intersections were found for the specified
     * type.
     */
    public List<Set<Resource>> getIntersectionsImplying(final Resource type) {
        if (intersections != null) {
            final List<Set<Resource>> intersectionList = intersections.get(type);
            return intersectionList;
        }
        return null;
    }

    /**
     * For a given type, return all sets of types such that owl:oneOf
     * restrictions on those properties could imply this type. A enumeration
     * of all the types that are part of the specified class type.
     * @param type The type (IRI or bnode) to check against the known oneOf
     * sets.
     * @return A {@link Set} of {@link Resource} types that represents the
     * enumeration of resources that belong to the class type.
     * An empty set is returned if no enumerations were found for the specified
     * type.
     */
    public Set<Resource> getEnumeration(final Resource type) {
        if (enumerations != null) {
            final Set<Resource> oneOfSet = enumerations.get(type);
            if (oneOfSet != null) {
                return oneOfSet;
            }
        }
        return new LinkedHashSet<>();

    }

    /**
     * Checks if the specified type is an enumerated type.
     * @param type The type (IRI or bnode) to check against the known oneOf
     * sets.
     * @return {@code true} if the type is an enumerated type. {@code false}
     * otherwise.
     */
    public boolean isEnumeratedType(final Resource type) {
        return enumerations != null && enumerations.containsKey(type);
    }
}