/// <summary>
/// Executes a Graph Pattern style query against the Source
/// </summary>
/// <param name="graph">Graph Pattern</param>
/// <param name="options">Query Options</param>
/// <param name="sink">Results Sink</param>
/// <remarks>
/// <para>
/// This is implemented by transforming the Graph Pattern which is a set of SemWeb Statement templates into a SPARQL Algebra BGP. The resulting algebra is then executed using the Leviathan engine and the results converted into VariableBindings for SemWeb
/// </para>
/// <para>
/// The only Query Option that is supported is the Limit option
/// </para>
/// </remarks>
public void Query(Statement[] graph, SW.Query.QueryOptions options, SW.Query.QueryResultSink sink)
{
ISparqlAlgebra algebra = this.ToAlgebra(graph);
SparqlEvaluationContext context = new SparqlEvaluationContext(null, new InMemoryDataset(this._store));
BaseMultiset results = context.Evaluate(algebra);//algebra.Evaluate(context);
sink.Init(results.Variables.Select(v => new Variable(v)).ToArray());
if (results.Count > 0)
{
int c = 0;
foreach (Set s in results.Sets)
{
//Apply Limit if applicable
if (options.Limit > 0 && c >= options.Limit)
{
sink.Finished();
return;
}
//Convert the Set to VariableBindings for SemWeb
Variable[] vars = s.Variables.Select(v => new Variable(v)).ToArray();
Resource[] resources = s.Variables.Select(v => SemWebConverter.ToSemWeb(s[v], this.GetMapping(s[v].Graph))).ToArray();
SW.Query.VariableBindings bindings = new SW.Query.VariableBindings(vars, resources);
//Keep adding results until the sink tells us to stop
if (!sink.Add(bindings))
{
sink.Finished();
return;
}
c++;
}
sink.Finished();
}
else
{
sink.Finished();
}
}
/// <summary>
/// Queries the Store using the Graph Pattern specified by the set of Statement Patterns
/// </summary>
/// <param name="graph">Graph Pattern</param>
/// <param name="options">Query Options</param>
/// <param name="sink">Results Sink</param>
/// <remarks>
/// <para>
/// Implemented by converting the Statement Patterns into a SPARQL SELECT query and executing that against the underlying Store's SPARQL engine
/// </para>
/// <para>
/// The only Query Option that is supported is the Limit option
/// </para>
/// </remarks>
public void Query(Statement[] graph, SW.Query.QueryOptions options, SW.Query.QueryResultSink sink)
{
//Implement as a SPARQL SELECT
SparqlParameterizedString queryString = new SparqlParameterizedString();
queryString.QueryText = "SELECT * WHERE {";
int p = 0;
foreach (Statement stmt in graph)
{
//Add Subject
queryString.QueryText += "\n";
if (stmt.Subject is Variable)
{
queryString.QueryText += stmt.Subject.ToString();
}
else
{
queryString.QueryText += "@param" + p;
queryString.SetParameter("param" + p, SemWebConverter.FromSemWeb(stmt.Subject, this._mapping));
p++;
}
queryString.QueryText += " ";
//Add Predicate
if (stmt.Predicate is Variable)
{
queryString.QueryText += stmt.Predicate.ToString();
}
else
{
queryString.QueryText += "@param" + p;
queryString.SetParameter("param" + p, SemWebConverter.FromSemWeb(stmt.Predicate, this._mapping));
p++;
}
queryString.QueryText += " ";
//Add Object
if (stmt.Object is Variable)
{
queryString.QueryText += stmt.Object.ToString();
}
else
{
queryString.QueryText += "@param" + p;
queryString.SetParameter("param" + p, SemWebConverter.FromSemWeb(stmt.Object, this._mapping));
p++;
}
queryString.QueryText += " .";
}
queryString.QueryText += "}";
//Execute the Query and convert the Results
Object results = this._store.ExecuteQuery(queryString.ToString());
if (results is SparqlResultSet)
{
SparqlResultSet rset = (SparqlResultSet)results;
sink.Init(rset.Variables.Select(v => new Variable(v)).ToArray());
if (rset.Count > 0)
{
int c = 0;
foreach (SparqlResult r in rset)
{
//Apply Limit if applicable
if (options.Limit > 0 && c >= options.Limit)
{
sink.Finished();
return;
}
//Convert the Set to VariableBindings for SemWeb
Variable[] vars = r.Variables.Select(v => new Variable(v)).ToArray();
Resource[] resources = r.Variables.Select(v => SemWebConverter.ToSemWeb(r[v], this._mapping)).ToArray();
SW.Query.VariableBindings bindings = new SW.Query.VariableBindings(vars, resources);
//Keep adding results until the sink tells us to stop
if (!sink.Add(bindings))
{
sink.Finished();
return;
}
c++;
}
sink.Finished();
}
else
{
sink.Finished();
}
}
else
{
throw new RdfQueryException("Query returned an unexpected result where a SPARQL Result Set was expected");
}
}
public void Query(Statement[] graph, SemWeb.Query.QueryOptions options, SemWeb.Query.QueryResultSink sink) {
if (graph.Length == 0) throw new ArgumentException("graph array must have at least one element");
// This method translates the graph pattern into a single SQL statement. Each graph statement
// corresponds to a new use of the _statements table in the FROM clause. For instance:
// ?a foaf:knows ?b . ?b foaf:name ?c .
// translates to
// SELECT
// g0.subject, v0.value,
// g0.object, v1.value,
// g1.object, v2.value, v2lit.value, v2lit.language, v2lit.datatype
// FROM
// db_tables as g0 LEFT JOIN db_entities AS v0 ON g0.subject=v0.id LEFT JOIN db_entities AS v1 ON g0.object=v1.id,
// db_tables as g1 LEFT JOIN db_entities AS v2 ON g1.object=v2.id LEFT JOIN db_literals AS v2lit ON g1.object=v2lit.id
// WHERE
// g0.predicate = <the id of the foaf:knows entity> AND
// g1.predicate = <the id of the foaf:name entity> AND
// g0.object = g1.subject
//
// If any variable column is an *undistinguished* variable --- which is to say that the caller
// says it is a variable, but is not concerned with its values --- then we want to apply
// DISTINCT to the SELECT statement. This is because while in the normal case we may get
// duplicates, we expect that to not occur more than the caller expects, but in the latter
// case there will often be many duplicates. Consider the SPARQL query:
// SELECT DISTINCT ?p WHERE { ?s ?p ?o }
// to get a list of predicates in the dataset, which corresponds to the graph query
// ?s ?p ?o
// where only ?p is distinguished.
// This normally translates to:
// SELECT
// g0.predicate, v0.value,
// FROM
// db_tables as g0 LEFT JOIN db_entities AS v0 ON g0.predicate=v0.id
// which of course is going to return a result for every triple in the database.
// So we add DISTINCT to beginning ("SELECT DISTINCT").
// Unfortunately, MySQL performs the DISTINCT bit only after the LEFT JOINs (which makes sense normally).
// That means that MySQL is repeatedly fetching the URI values of the predicates and checking
// if a new unique row has been created, and this is very slow. What we want is to get the distinct
// IDs of the predicates first, and then get their URIs.
// I first tried implementing this with VIEWs, but it didn't always speed things up, and it was
// difficult to manage the creation and deletion of VIEWs.
// So instead, in this case, we do the query in two parts. First we get the IDs of the variables,
// and then we get their URIs.
options = options.Clone(); // because we modify the knownvalues array
// Order the variables mentioned in the graph.
Variable[] varOrder;
ResSet distinguishedVars = null;
bool useDistinct = false;
{
if (options.DistinguishedVariables != null)
distinguishedVars = new ResSet(options.DistinguishedVariables);
else
distinguishedVars = new ResSet();
Hashtable seenvars = new Hashtable();
foreach (Statement filter in graph) {
for (int i = 0; i < 4; i++) {
Resource r = filter.GetComponent(i);
if (r == null)
throw new ArgumentException("The graph may not have any null components. Use Variables instead.");
if (r is Variable) {
if (options.DistinguishedVariables != null) {
if (!distinguishedVars.Contains(r)) {
// If we are omitting a column from the results because it is
// not distinguished, and it's not a meta column, then we'll
// use DISTINCT.
if (i != 3)
useDistinct = true;
// Don't put this into seenvars.
continue;
}
} else {
distinguishedVars.Add(r); // all variables are distinguished
}
seenvars[r] = r;
}
}
}
varOrder = new Variable[seenvars.Count];
int ctr = 0;
foreach (Variable v in seenvars.Keys)
varOrder[ctr++] = v;
}
// Set the initial bindings to the result sink
sink.Init(varOrder);
Hashtable varLitFilters = new Hashtable();
// Prefetch the IDs of all resources mentioned in the graph and in variable known values.
// For Resources in the graph that are not in the store, the query immediately fails.
{
ArrayList graphResources = new ArrayList();
foreach (Statement s in graph) {
for (int i = 0; i < 4; i++) {
Resource r = s.GetComponent(i);
if (!(r is BNode)) // definitely exclude variables, but bnodes are useless too
graphResources.Add(r);
}
}
if (options.VariableKnownValues != null)
foreach (ICollection values in options.VariableKnownValues.Values)
graphResources.AddRange(values);
PrefetchResourceIds(graphResources);
// Check resources in graph and fail fast if any is not in the store.
foreach (Statement s in graph) {
for (int i = 0; i < 4; i++) {
Resource r = s.GetComponent(i);
if (r is Variable) continue;
if ((object)r != (object)Statement.DefaultMeta && GetResourceKey(r) == null) {
sink.AddComments("Resource " + r + " is not contained in the data model.");
sink.Finished();
return;
}
}
}
// Check variable known values and remove any values not in the store.
// Don't do any fail-fasting here because there might be entries in this
// dictionary that aren't even used in this query (yes, poor design).
// We check later anyway.
if (options.VariableKnownValues != null) {
#if !DOTNET2
foreach (Variable v in new ArrayList(options.VariableKnownValues.Keys)) {
#else
foreach (Variable v in new System.Collections.Generic.List<Variable>(options.VariableKnownValues.Keys)) {
#endif
#if !DOTNET2
ArrayList newvalues = new ArrayList();
#else
System.Collections.Generic.List<Resource> newvalues = new System.Collections.Generic.List<Resource>();
#endif
foreach (Resource r in (ICollection)options.VariableKnownValues[v]) {
if ((object)r == (object)Statement.DefaultMeta || GetResourceKey(r) != null)
newvalues.Add(r);
}
options.VariableKnownValues[v] = newvalues;
}
}
}
// Helpers
string[] colnames = { "subject", "predicate", "object", "meta" };
// we initialize these things while locked, but use them after we release the lock
ArrayList results = new ArrayList();
Hashtable resourceCache = new Hashtable(); // map resource ID to Resource instances
// We can either include JOINs to the entities and literals table for every variable
// in the query, or we can delay fetching that information to separate SELECTs
// after the main part of the query is done. If we are including DISTINCT, then we
// don't want to do the JOINs because the JOINs happen before the DISTINCT and will
// be unnecessarily repeated. Also if the query has many variables, say more than 6,
// then it may slow down query planning (the MySQL optimizer) to include them all in
// one query.
bool joinEntitiesAndLiterals = true;
if (useDistinct) joinEntitiesAndLiterals = false;
if (varOrder.Length > 6) joinEntitiesAndLiterals = false;
// Lock the store and make sure we are initialized and any pending add's have been committed.
lock (syncroot) {
Init();
RunAddBuffer();
// Compile the SQL statement.
Hashtable varRef = new Hashtable(); // the column name representing the variable, as in "g0.subject"
Hashtable varRef2 = new Hashtable(); // the index of the variable, for accessing the entities and literals joined tables
Hashtable varSelectedLiteral = new Hashtable(); // whether the variable is in a literal column and a LEFT JOIN for the literals table was used for it
Hashtable varCouldBeLiteral = new Hashtable(); // whether the variable is only in literal columns
Hashtable varSelectedEntity = new Hashtable(); // whether a LEFT JOIN for the entities table was used for a variable
StringBuilder fromClause = new StringBuilder();
StringBuilder whereClause = new StringBuilder();
for (int f = 0; f < graph.Length; f++) {
// For each filter, we select FROM the statements table with an
// alias: q#, where # is the filter's index.
if (f > 0) fromClause.Append(',');
fromClause.Append(table);
fromClause.Append("_statements AS g");
fromClause.Append(f);
// For each component of the filter...
for (int i = 0; i < 4; i++) {
// This has the name of the column corresponding to this variable (i.e. "g1.predicate").
string myRef = "g" + f + "." + colnames[i];
Variable v = graph[f].GetComponent(i) as Variable;
if (v != null) {
// If the component is a variable, then if this is
// the first time we're seeing the variable, we don't
// add any restrictions to the WHERE clause, but we
// note the variable's "name" in the world of SQL
// so we can refer back to it later and we add the
// necessary FROM tables so we can get its URI and
// literal value if it is a reported variable.
// If this isn't the first time, then we add a WHERE restriction so
// that the proper columns here and in a previous
// filter are forced to have the same value.
if (!varRef.ContainsKey(v)) {
// This is the first time we are seeing this variable.
// Record the column name for the variable (i.e. g0.subject).
varRef[v] = myRef;
// Record an index for the variable (i.e. 0, 1, 2, ...)
int vIndex = varRef.Count;
varRef2[v] = vIndex;
varCouldBeLiteral[v] = (i == 2);
// LEFT JOIN the entities table for this variable to get its URI
// only if it is a distinguished variable and we are not using DISTINCT.
varSelectedEntity[v] = false;
if (joinEntitiesAndLiterals && distinguishedVars.Contains(v)) {
varSelectedEntity[v] = true; // Record that we are selecting the entities table for this variable.
fromClause.Append(" LEFT JOIN ");
fromClause.Append(table);
fromClause.Append("_entities AS vent");
fromClause.Append(vIndex);
fromClause.Append(" ON ");
fromClause.Append(myRef);
fromClause.Append("=");
fromClause.Append("vent" + vIndex + ".id ");
}
// LEFT JOIN the literals table for this variable:
// if it is in an object position
// to get its value, language, and datatype only if it is a distinguished variable and we are not using DISTINCT
// to apply a literal value filter (which will be done later)
#if !DOTNET2
bool hasLitFilter = (options.VariableLiteralFilters != null && options.VariableLiteralFilters[v] != null);
#else
bool hasLitFilter = (options.VariableLiteralFilters != null && options.VariableLiteralFilters.ContainsKey(v));
#endif
varSelectedLiteral[v] = false;
if (i == 2 && ((joinEntitiesAndLiterals && distinguishedVars.Contains(v)) || hasLitFilter)) {
varSelectedLiteral[v] = true; // Record that we are selecting the literals table for this variable.
fromClause.Append(" LEFT JOIN ");
fromClause.Append(table);
fromClause.Append("_literals AS vlit");
fromClause.Append(vIndex);
fromClause.Append(" ON ");
fromClause.Append(myRef);
fromClause.Append("=");
fromClause.Append("vlit" + vIndex + ".id ");
}
// If this variable has known values, then we must restrict what values can appear using a WHERE clause.
if (options.VariableKnownValues != null) {
ICollection values = null;
#if DOTNET2
if (options.VariableKnownValues.ContainsKey(v))
#endif
values = (ICollection)options.VariableKnownValues[v];
if (values != null) {
if (values.Count == 0) {
sink.Finished();
return;
}
Resource r = ToMultiRes((Resource[])new ArrayList(values).ToArray(typeof(Resource)));
if (!WhereItem(myRef, r, whereClause, whereClause.Length != 0)) {
// We know at this point that the query cannot return any results.
sink.Finished();
return;
}
}
}
} else {
// We've seen this variable before, so link up the column in this
// statement to the corresponding column in a previous (or this) statement.
if (whereClause.Length != 0) whereClause.Append(" AND ");
whereClause.Append('(');
whereClause.Append((string)varRef[v]);
whereClause.Append('=');
whereClause.Append(myRef);
whereClause.Append(')');
if (i != 2)
varCouldBeLiteral[v] = false;
}
} else {
// If this is not a variable, then it is a resource.
// Append something into the WHERE clause to make sure this component gets
// the right fixed value. If we cannot add the component to the WHERE clause
// because the fixed value isn't even known in the data source, we can stop early.
if (!WhereItem(myRef, graph[f].GetComponent(i), whereClause, whereClause.Length != 0)) {
// We know at this point that the query cannot return any results.
sink.Finished();
return;
}
}
}
} // graph filter 0...n
// Add literal filters to the WHERE clause
foreach (Variable v in varOrder) {
// Is there a literal value filter?
if (options.VariableLiteralFilters == null) continue;
#if !DOTNET2
if (options.VariableLiteralFilters[v] == null) continue;
#else
if (!options.VariableLiteralFilters.ContainsKey(v)) continue;
#endif
// If this variable was not used in a literal column, then
// we cannot filter its value. Really, it will never be a literal.
if (!(bool)varSelectedLiteral[v]) continue;
foreach (LiteralFilter filter in (ICollection)options.VariableLiteralFilters[v]) {
string s = FilterToSQL(filter, "vlit" + (int)varRef2[v] + ".value");
if (s == null) continue;
if (whereClause.Length != 0) whereClause.Append(" AND ");
whereClause.Append(s);
}
}
// Put the parts of the SQL statement together
StringBuilder cmd = new StringBuilder();
cmd.Append("SELECT ");
if (useDistinct) cmd.Append("DISTINCT ");
if (!SupportsLimitClause && options.Limit > 0) {
cmd.Append("TOP ");
cmd.Append(options.Limit);
cmd.Append(' ');
}
// Add all of the distinguished variables to the SELECT clause.
bool firstvar = true;
foreach (Variable v in varOrder) {
if (!firstvar) cmd.Append(','); firstvar = false;
cmd.Append((string)varRef[v]);
if ((bool)varSelectedEntity[v]) {
cmd.Append(", vent" + (int)varRef2[v] + ".value");
}
if ((bool)varSelectedLiteral[v]) {
cmd.Append(", vlit" + (int)varRef2[v] + ".value");
cmd.Append(", vlit" + (int)varRef2[v] + ".language");
cmd.Append(", vlit" + (int)varRef2[v] + ".datatype");
}
}
cmd.Append(" FROM ");
cmd.Append(fromClause.ToString());
if (whereClause.Length > 0)
cmd.Append(" WHERE ");
cmd.Append(whereClause.ToString());
if (SupportsLimitClause && options.Limit > 0) {
cmd.Append(" LIMIT ");
cmd.Append(options.Limit);
}
cmd.Append(';');
if (Debug) {
string cmd2 = cmd.ToString();
//if (cmd2.Length > 80) cmd2 = cmd2.Substring(0, 80);
Console.Error.WriteLine(cmd2);
}
// Execute the query.
// When we use DISTINCT and don't select URI and literal values at first,
// we have to select them after. And since we can't maintain two IDataReaders
// simultaneously, that means we have to pull the first set of results into
// memory. It would be nice to not have to do that when we don't use DISTINCT,
// but in practice it doesn't really matter since in SPARQL it's all sucked
// into memory anyway.
using (IDataReader reader = RunReader(cmd.ToString())) {
while (reader.Read()) {
QueryResultRowVariable[] row = new QueryResultRowVariable[varOrder.Length];
results.Add(row);
int col = 0;
for (int i = 0; i < varOrder.Length; i++) {
Variable v = varOrder[i];
row[i].id = reader.GetInt64(col++);
if ((bool)varSelectedEntity[v]) {
row[i].uri = AsString(reader[col++]);
}
if ((bool)varSelectedLiteral[v]) {
row[i].litvalue = AsString(reader[col++]);
row[i].litlanguage = AsString(reader[col++]);
row[i].litdatatype = AsString(reader[col++]);
}
}
}
}
// For any distinguished variable that we did not select URIs or literal values for,
// select that information now.
for (int i = 0; i < varOrder.Length; i++) {
Variable v = varOrder[i];
if ((bool)varSelectedEntity[v] && (!(bool)varCouldBeLiteral[v] || (bool)varSelectedLiteral[v])) continue;
// Get the list of resource IDs found for this variable.
ArrayList rids = new ArrayList();
foreach (QueryResultRowVariable[] row in results) {
if (row[i].id <= 1) continue; // can't fetch for Statement.DefaultMeta
if (resourceCache.ContainsKey(row[i].id)) continue; // we've already fetched it
rids.Add(row[i].id); // probably no need to remove duplicates
}
if (rids.Count > 0) {
// Fetch what we can for entities.
if (!(bool)varSelectedEntity[v]) {
StringBuilder cmd2 = new StringBuilder();
cmd2.Append("SELECT id, value FROM ");
cmd2.Append(table);
cmd2.Append("_entities WHERE id IN (");
bool first = true;
foreach (Int64 id in rids) {
if (!first) cmd2.Append(','); first = false;
cmd2.Append(id);
}
cmd2.Append(")");
if (Debug) { Console.Error.WriteLine(cmd2.ToString()); }
using (IDataReader reader = RunReader(cmd2.ToString())) {
while (reader.Read()) {
Int64 id = reader.GetInt64(0);
string uri = AsString(reader[1]);
resourceCache[id] = MakeEntity(id, uri, null);
}
}
}
// Fetch what we can for literals.
if ((bool)varCouldBeLiteral[v] && !(bool)varSelectedLiteral[v]) {
StringBuilder cmd2 = new StringBuilder();
cmd2.Append("SELECT id, value, language, datatype FROM ");
cmd2.Append(table);
cmd2.Append("_literals WHERE id IN (");
bool first = true;
foreach (Int64 id in rids)
{
if (!first) cmd2.Append(','); first = false;
cmd2.Append(id);
}
cmd2.Append(")");
if (Debug) { Console.Error.WriteLine(cmd2.ToString()); }
using (IDataReader reader = RunReader(cmd2.ToString())) {
while (reader.Read()) {
Int64 id = reader.GetInt64(0);
string value = AsString(reader[1]);
string language = AsString(reader[2]);
string datatype = AsString(reader[3]);
Literal lit = new Literal(value, language, datatype);
SetResourceKey(lit, new ResourceKey(id));
resourceCache[id] = lit;
}
}
}
// Any ids not found so far are bnodes.
foreach (Int64 id in rids)
{
if (!resourceCache.ContainsKey(id)) {
BNode b = new BNode();
SetResourceKey(b, new ResourceKey(id));
resourceCache[id] = b;
}
}
}
}
} // lock
// Now loop through the binding results.
foreach (QueryResultRowVariable[] row in results) {
bool match = true;
Resource[] variableBindings = new Resource[varOrder.Length];
for (int i = 0; i < varOrder.Length; i++) {
Int64 id = row[i].id;
if (resourceCache.ContainsKey(id)) {
variableBindings[i] = (Resource)resourceCache[id];
} else {
if (row[i].litvalue == null) {
variableBindings[i] = MakeEntity(id, row[i].uri, null);
} else {
Literal lit = new Literal(row[i].litvalue, row[i].litlanguage, row[i].litdatatype);
ArrayList litFilters = (ArrayList)varLitFilters[varOrder[i]];
if (litFilters != null && !LiteralFilter.MatchesFilters(lit, (LiteralFilter[])litFilters.ToArray(typeof(LiteralFilter)), this)) {
match = false;
break;
}
SetResourceKey(lit, new ResourceKey(id));
variableBindings[i] = lit;
}
// reuse this entity later
resourceCache[id] = variableBindings[i];
}
}
if (!match) continue;
if (!sink.Add(new SemWeb.Query.VariableBindings(varOrder, variableBindings))) return;
}
sink.Finished();
}
public override void Query(Statement[] graph, SemWeb.Query.QueryOptions options, SelectableSource targetModel, SemWeb.Query.QueryResultSink sink)
{
QueryCheckArg(graph);
// Try to do the inferencing.
ArrayList evidence = prove(rules, targetModel, graph, -1);
if (evidence == null)
return; // not provable (in max number of steps, if that were given)
// Then send the possible bindings to the QueryResultSink.
// Map variables to indexes.
Hashtable vars = new Hashtable();
foreach (Statement s in graph) {
if (s.Subject is Variable && !vars.ContainsKey(s.Subject)) vars[s.Subject] = vars.Count;
if (s.Predicate is Variable && !vars.ContainsKey(s.Predicate)) vars[s.Predicate] = vars.Count;
if (s.Object is Variable && !vars.ContainsKey(s.Object)) vars[s.Object] = vars.Count;
}
// Prepare the bindings array.
Variable[] varOrder = new Variable[vars.Count];
foreach (Variable v in vars.Keys)
varOrder[(int)vars[v]] = v;
// Initialize the sink.
sink.Init(varOrder);
// Send a binding set for each piece of evidence.
foreach (EvidenceItem ei in evidence) {
// Write a comment to the results with the actual proof. (nifty actually)
sink.AddComments(ei.ToProof().ToString());
// Create the binding array and send it on
Resource[] variableBindings = new Resource[varOrder.Length];
foreach (Variable v in vars.Keys)
if (ei.env.ContainsKey(v))
variableBindings[(int)vars[v]] = (Resource)ei.env[v];
sink.Add(new SemWeb.Query.VariableBindings(varOrder, variableBindings));
}
// Close the sink.
sink.Finished();
}