/// <summary>
/// Evaluates the Ask Union
/// </summary>
/// <param name="context">Evaluation Context</param>
/// <returns></returns>
public BaseMultiset Evaluate(SparqlEvaluationContext context)
{
BaseMultiset initialInput = context.InputMultiset;
if (this._lhs is Extend || this._rhs is Extend)
{
initialInput = new IdentityMultiset();
}
context.InputMultiset = initialInput;
BaseMultiset lhsResult = context.Evaluate(this._lhs);//this._lhs.Evaluate(context);
context.CheckTimeout();
if (lhsResult.IsEmpty)
{
//Only evaluate the RHS if the LHS was empty
context.InputMultiset = initialInput;
BaseMultiset rhsResult = context.Evaluate(this._rhs);//this._rhs.Evaluate(context);
context.CheckTimeout();
context.OutputMultiset = lhsResult.Union(rhsResult);
context.CheckTimeout();
context.InputMultiset = context.OutputMultiset;
}
else
{
context.OutputMultiset = lhsResult;
}
return(context.OutputMultiset);
}
/// <summary>
/// Evaluates the Lazy Union.
/// </summary>
/// <param name="context">Evaluation Context.</param>
/// <returns></returns>
public BaseMultiset Evaluate(SparqlEvaluationContext context)
{
BaseMultiset initialInput = context.InputMultiset;
if (_lhs is Extend || _rhs is Extend)
{
initialInput = new IdentityMultiset();
}
context.InputMultiset = initialInput;
BaseMultiset lhsResult = context.Evaluate(_lhs); //this._lhs.Evaluate(context);
context.CheckTimeout();
if (lhsResult.Count >= _requiredResults || _requiredResults == -1)
{
// Only evaluate the RHS if the LHS didn't yield sufficient results
context.InputMultiset = initialInput;
BaseMultiset rhsResult = context.Evaluate(_rhs); //this._rhs.Evaluate(context);
context.CheckTimeout();
context.OutputMultiset = lhsResult.Union(rhsResult);
context.CheckTimeout();
context.InputMultiset = context.OutputMultiset;
}
else
{
context.OutputMultiset = lhsResult;
}
return(context.OutputMultiset);
}
/// <summary>
/// Evaluates the Union
/// </summary>
/// <param name="context"></param>
/// <returns></returns>
public BaseMultiset Evaluate(SparqlEvaluationContext context)
{
BaseMultiset initialInput = context.InputMultiset;
if (_lhs is Extend || _rhs is Extend)
{
initialInput = new IdentityMultiset();
}
context.InputMultiset = initialInput;
BaseMultiset lhsResult = context.Evaluate(_lhs);
context.CheckTimeout();
context.InputMultiset = initialInput;
BaseMultiset rhsResult = context.Evaluate(_rhs);
context.CheckTimeout();
context.OutputMultiset = lhsResult.Union(rhsResult);
context.CheckTimeout();
context.InputMultiset = context.OutputMultiset;
return(context.OutputMultiset);
}
public void SparqlMultisetLeftJoin()
{
//Create a load of Nodes to use in the tests
Graph g = new Graph();
g.NamespaceMap.AddNamespace(String.Empty, new Uri("http://example.org"));
IUriNode s1 = g.CreateUriNode(":s1");
IUriNode s2 = g.CreateUriNode(":s2");
IUriNode p1 = g.CreateUriNode(":p1");
IUriNode p2 = g.CreateUriNode(":p2");
IUriNode rdfsLabel = g.CreateUriNode("rdfs:label");
ILiteralNode o1 = g.CreateLiteralNode("Some Text");
ILiteralNode o2 = g.CreateLiteralNode("1", new Uri(XmlSpecsHelper.XmlSchemaDataTypeInteger));
//Create an ID and Null Multiset
IdentityMultiset id = new IdentityMultiset();
NullMultiset nullset = new NullMultiset();
//Create and Populate a Multiset
Multiset m = new Multiset();
Set s = new Set();
s.Add("s", s1);
s.Add("p", p1);
s.Add("o", o1);
m.Add(s);
s = new Set();
s.Add("s", s2);
s.Add("p", p2);
s.Add("o", o2);
m.Add(s);
//Create and Populate another Multiset
Multiset n = new Multiset();
s = new Set();
s.Add("s", s1);
s.Add("label", o1);
n.Add(s);
//Create and Populate another Multiset
Multiset d = new Multiset();
s = new Set();
s.Add("s1", s1);
s.Add("p1", p1);
s.Add("o1", o1);
d.Add(s);
s = new Set();
s.Add("s1", s2);
s.Add("p1", p2);
s.Add("o1", o2);
d.Add(s);
//Show the Sets
Console.WriteLine("LHS");
foreach (Set set in m.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
Console.WriteLine("RHS");
foreach (Set set in n.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
Console.WriteLine("D");
foreach (Set set in d.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a Join to Identity
Console.WriteLine("Join ID-LHS");
BaseMultiset join = id.Join(m);
foreach (Set set in join.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a Join to Identity
Console.WriteLine("Join LHS-ID");
join = m.Join(id);
foreach (Set set in join.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a Join to Null
Console.WriteLine("Join NULL-LHS");
join = nullset.Join(m);
foreach (Set set in join.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a Join to Null
Console.WriteLine("Join LHS-NULL");
join = m.Join(nullset);
foreach (Set set in join.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a LeftJoin
Console.WriteLine("LeftJoin NULL-LHS");
BaseMultiset leftjoin = nullset.LeftJoin(m, new BooleanExpressionTerm(true));
foreach (Set set in leftjoin.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a LeftJoin
Console.WriteLine("LeftJoin LHS-NULL");
leftjoin = m.LeftJoin(nullset, new BooleanExpressionTerm(true));
foreach (Set set in leftjoin.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a Join
Console.WriteLine("Join LHS-RHS");
join = m.Join(n);
foreach (Set set in join.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a LeftOuterJoin
Console.WriteLine("LeftJoin LHS-RHS");
leftjoin = m.LeftJoin(n, new BooleanExpressionTerm(true));
foreach (Set set in leftjoin.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a Produce
Console.WriteLine("Product LHS-RHS");
BaseMultiset product = m.Product(n);
foreach (Set set in product.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a Join to Self
Console.WriteLine("Product LHS-D");
product = m.Product(d);
foreach (Set set in product.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
//Try a Union
Console.WriteLine("Union LHS-RHS");
BaseMultiset union = m.Union(n);
foreach (Set set in union.Sets)
{
Console.WriteLine(set.ToString());
}
Console.WriteLine();
}
private BaseMultiset StreamingEvaluate(SparqlEvaluationContext context, int pattern, out bool halt)
{
halt = false;
//Handle Empty BGPs
if (pattern == 0 && this._triplePatterns.Count == 0)
{
context.OutputMultiset = new IdentityMultiset();
return(context.OutputMultiset);
}
BaseMultiset initialInput, localOutput, results = null;
//Determine whether the Pattern modifies the existing Input rather than joining to it
bool modifies = (this._triplePatterns[pattern] is FilterPattern);
bool extended = (pattern > 0 && this._triplePatterns[pattern - 1] is BindPattern);
bool modified = (pattern > 0 && this._triplePatterns[pattern - 1] is FilterPattern);
//Set up the Input and Output Multiset appropriately
switch (pattern)
{
case 0:
//Input is as given and Output is new empty multiset
if (!modifies)
{
initialInput = context.InputMultiset;
}
else
{
//If the Pattern will modify the Input and is the first thing in the BGP then it actually modifies a new empty input
//This takes care of FILTERs being out of scope
initialInput = new Multiset();
}
localOutput = new Multiset();
break;
case 1:
//Input becomes current Output and Output is new empty multiset
initialInput = context.OutputMultiset;
localOutput = new Multiset();
break;
default:
if (!extended && !modified)
{
//Input is join of previous input and output and Output is new empty multiset
if (context.InputMultiset.IsDisjointWith(context.OutputMultiset))
{
//Disjoint so do a Product
initialInput = context.InputMultiset.ProductWithTimeout(context.OutputMultiset, context.RemainingTimeout);
}
else
{
//Normal Join
initialInput = context.InputMultiset.Join(context.OutputMultiset);
}
}
else
{
initialInput = context.OutputMultiset;
}
localOutput = new Multiset();
break;
}
context.InputMultiset = initialInput;
context.OutputMultiset = localOutput;
//Get the Triple Pattern we're evaluating
ITriplePattern temp = this._triplePatterns[pattern];
int resultsFound = 0;
int prevResults = -1;
if (temp is TriplePattern)
{
//Find the first Triple which matches the Pattern
TriplePattern tp = (TriplePattern)temp;
IEnumerable <Triple> ts = tp.GetTriples(context);
//In the case that we're lazily evaluating an optimisable ORDER BY then
//we need to apply OrderBy()'s to our enumeration
//This only applies to the 1st pattern
if (pattern == 0)
{
if (context.Query != null)
{
if (context.Query.OrderBy != null && context.Query.IsOptimisableOrderBy)
{
IComparer <Triple> comparer = context.Query.OrderBy.GetComparer(tp);
if (comparer != null)
{
ts = ts.OrderBy(t => t, comparer);
}
else
{
//Can't get a comparer so can't optimise
this._requiredResults = -1;
}
}
}
}
foreach (Triple t in ts)
{
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
if (tp.Accepts(context, t))
{
resultsFound++;
if (tp.IndexType == TripleIndexType.NoVariables)
{
localOutput = new IdentityMultiset();
context.OutputMultiset = localOutput;
}
else
{
context.OutputMultiset.Add(tp.CreateResult(t));
}
//Recurse unless we're the last pattern
if (pattern < this._triplePatterns.Count - 1)
{
results = this.StreamingEvaluate(context, pattern + 1, out halt);
//If recursion leads to a halt then we halt and return immediately
if (halt && results.Count >= this._requiredResults && this._requiredResults != -1)
{
return(results);
}
else if (halt)
{
if (results.Count == 0)
{
//If recursing leads to no results then eliminate all outputs
//Also reset to prevResults to -1
resultsFound = 0;
localOutput = new Multiset();
prevResults = -1;
}
else if (prevResults > -1)
{
if (results.Count == prevResults)
{
//If the amount of results found hasn't increased then this match does not
//generate any further solutions further down the recursion so we can eliminate
//this from the results
localOutput.Remove(localOutput.SetIDs.Max());
}
}
prevResults = results.Count;
//If we're supposed to halt but not reached the number of required results then continue
context.InputMultiset = initialInput;
context.OutputMultiset = localOutput;
}
else
{
//Otherwise we need to keep going here
//So must reset our input and outputs before continuing
context.InputMultiset = initialInput;
context.OutputMultiset = new Multiset();
resultsFound--;
}
}
else
{
//If we're at the last pattern and we've found a match then we can halt
halt = true;
//Generate the final output and return it
if (context.InputMultiset.IsDisjointWith(context.OutputMultiset))
{
//Disjoint so do a Product
results = context.InputMultiset.ProductWithTimeout(context.OutputMultiset, context.RemainingTimeout);
}
else
{
//Normal Join
results = context.InputMultiset.Join(context.OutputMultiset);
}
//If not reached required number of results continue
if (results.Count >= this._requiredResults && this._requiredResults != -1)
{
context.OutputMultiset = results;
return(context.OutputMultiset);
}
}
}
}
}
else if (temp is FilterPattern)
{
FilterPattern filter = (FilterPattern)temp;
ISparqlExpression filterExpr = filter.Filter.Expression;
if (filter.Variables.IsDisjoint(context.InputMultiset.Variables))
{
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
//Filter is Disjoint so determine whether it has any affect or not
if (filter.Variables.Any())
{
//Has Variables but disjoint from input => not in scope so gets ignored
//Do we recurse or not?
if (pattern < this._triplePatterns.Count - 1)
{
//Recurse and return
results = this.StreamingEvaluate(context, pattern + 1, out halt);
return(results);
}
else
{
//We don't affect the input in any way so just return it
return(context.InputMultiset);
}
}
else
{
//No Variables so have to evaluate it to see if it gives true otherwise
try
{
if (filterExpr.EffectiveBooleanValue(context, 0))
{
if (pattern < this._triplePatterns.Count - 1)
{
//Recurse and return
results = this.StreamingEvaluate(context, pattern + 1, out halt);
return(results);
}
else
{
//Last Pattern and we evaluate to true so can return the input as-is
halt = true;
return(context.InputMultiset);
}
}
}
catch (RdfQueryException)
{
//Evaluates to false so eliminates all solutions (use an empty Multiset)
return(new Multiset());
}
}
}
else
{
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
//Test each solution found so far against the Filter and eliminate those that evalute to false/error
foreach (int id in context.InputMultiset.SetIDs.ToList())
{
try
{
if (filterExpr.EffectiveBooleanValue(context, id))
{
//If evaluates to true then add to output
context.OutputMultiset.Add(context.InputMultiset[id]);
}
}
catch (RdfQueryException)
{
//Error means we ignore the solution
}
}
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
//Decide whether to recurse or not
resultsFound = context.OutputMultiset.Count;
if (pattern < this._triplePatterns.Count - 1)
{
//Recurse then return
//We can never decide whether to recurse again at this point as we are not capable of deciding
//which solutions should be dumped (that is the job of an earlier pattern in the BGP)
results = this.StreamingEvaluate(context, pattern + 1, out halt);
return(results);
}
else
{
halt = true;
//However many results we need we'll halt - previous patterns can call us again if they find more potential solutions
//for us to filter
return(context.OutputMultiset);
}
}
}
else if (temp is BindPattern)
{
BindPattern bind = (BindPattern)temp;
ISparqlExpression bindExpr = bind.AssignExpression;
String bindVar = bind.VariableName;
if (context.InputMultiset.ContainsVariable(bindVar))
{
throw new RdfQueryException("Cannot use a BIND assigment to BIND to a variable that has previously been used in the Query");
}
else
{
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
//Compute the Binding for every value
context.OutputMultiset.AddVariable(bindVar);
foreach (ISet s in context.InputMultiset.Sets)
{
ISet x = s.Copy();
try
{
INode val = bindExpr.Value(context, s.ID);
x.Add(bindVar, val);
}
catch (RdfQueryException)
{
//Equivalent to no assignment but the solution is preserved
}
context.OutputMultiset.Add(x);
}
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
//Decide whether to recurse or not
resultsFound = context.OutputMultiset.Count;
if (pattern < this._triplePatterns.Count - 1)
{
//Recurse then return
results = this.StreamingEvaluate(context, pattern + 1, out halt);
return(results);
}
else
{
halt = true;
//However many results we need we'll halt - previous patterns can call us again if they find more potential solutions
//for us to extend
return(context.OutputMultiset);
}
}
}
else
{
throw new RdfQueryException("Encountered a " + temp.GetType().FullName + " which is not a lazily evaluable Pattern");
}
//If we found no possibles we return the null multiset
if (resultsFound == 0)
{
return(new NullMultiset());
}
else
{
//Generate the final output and return it
if (!modifies)
{
if (context.InputMultiset.IsDisjointWith(context.OutputMultiset))
{
//Disjoint so do a Product
results = context.InputMultiset.ProductWithTimeout(context.OutputMultiset, context.RemainingTimeout);
}
else
{
//Normal Join
results = context.InputMultiset.Join(context.OutputMultiset);
}
context.OutputMultiset = results;
}
return(context.OutputMultiset);
}
}
/// <summary>
/// Evaluates the Ask Union
/// </summary>
/// <param name="context">Evaluation Context</param>
/// <returns></returns>
public BaseMultiset Evaluate(SparqlEvaluationContext context)
{
BaseMultiset initialInput = context.InputMultiset;
if (this._lhs is Extend || this._rhs is Extend) initialInput = new IdentityMultiset();
context.InputMultiset = initialInput;
BaseMultiset lhsResult = context.Evaluate(this._lhs);//this._lhs.Evaluate(context);
context.CheckTimeout();
if (lhsResult.IsEmpty)
{
//Only evaluate the RHS if the LHS was empty
context.InputMultiset = initialInput;
BaseMultiset rhsResult = context.Evaluate(this._rhs);//this._rhs.Evaluate(context);
context.CheckTimeout();
context.OutputMultiset = lhsResult.Union(rhsResult);
context.CheckTimeout();
context.InputMultiset = context.OutputMultiset;
}
else
{
context.OutputMultiset = lhsResult;
}
return context.OutputMultiset;
}
/// <summary>
/// Evaluates the Union
/// </summary>
/// <param name="context"></param>
/// <returns></returns>
public BaseMultiset Evaluate(SparqlEvaluationContext context)
{
BaseMultiset initialInput = context.InputMultiset;
if (this._lhs is Extend || this._rhs is Extend) initialInput = new IdentityMultiset();
context.InputMultiset = initialInput;
BaseMultiset lhsResult = context.Evaluate(this._lhs);//this._lhs.Evaluate(context);
context.CheckTimeout();
context.InputMultiset = initialInput;
BaseMultiset rhsResult = context.Evaluate(this._rhs);//this._rhs.Evaluate(context);
context.CheckTimeout();
context.OutputMultiset = lhsResult.Union(rhsResult);
context.CheckTimeout();
context.InputMultiset = context.OutputMultiset;
return context.OutputMultiset;
}
/// <summary>
/// Evaluates the Lazy Union
/// </summary>
/// <param name="context">Evaluation Context</param>
/// <returns></returns>
public BaseMultiset Evaluate(SparqlEvaluationContext context)
{
BaseMultiset initialInput = context.InputMultiset;
if (this._lhs is Extend || this._rhs is Extend) initialInput = new IdentityMultiset();
context.InputMultiset = initialInput;
BaseMultiset lhsResult = context.Evaluate(this._lhs);//this._lhs.Evaluate(context);
context.CheckTimeout();
if (lhsResult.Count >= this._requiredResults || this._requiredResults == -1)
{
//Only evaluate the RHS if the LHS didn't yield sufficient results
context.InputMultiset = initialInput;
BaseMultiset rhsResult = context.Evaluate(this._rhs);//this._rhs.Evaluate(context);
context.CheckTimeout();
context.OutputMultiset = lhsResult.Union(rhsResult);
context.CheckTimeout();
context.InputMultiset = context.OutputMultiset;
}
else
{
context.OutputMultiset = lhsResult;
}
return context.OutputMultiset;
}
private BaseMultiset StreamingEvaluate(SparqlEvaluationContext context, int pattern, out bool halt)
{
halt = false;
//Handle Empty BGPs
if (pattern == 0 && this._triplePatterns.Count == 0)
{
context.OutputMultiset = new IdentityMultiset();
return context.OutputMultiset;
}
BaseMultiset initialInput, localOutput, results = null;
//Determine whether the Pattern modifies the existing Input rather than joining to it
bool modifies = (this._triplePatterns[pattern] is FilterPattern);
bool extended = (pattern > 0 && this._triplePatterns[pattern-1] is BindPattern);
bool modified = (pattern > 0 && this._triplePatterns[pattern-1] is FilterPattern);
//Set up the Input and Output Multiset appropriately
switch (pattern)
{
case 0:
//Input is as given and Output is new empty multiset
if (!modifies)
{
initialInput = context.InputMultiset;
}
else
{
//If the Pattern will modify the Input and is the first thing in the BGP then it actually modifies a new empty input
//This takes care of FILTERs being out of scope
initialInput = new Multiset();
}
localOutput = new Multiset();
break;
case 1:
//Input becomes current Output and Output is new empty multiset
initialInput = context.OutputMultiset;
localOutput = new Multiset();
break;
default:
if (!extended && !modified)
{
//Input is join of previous input and output and Output is new empty multiset
if (context.InputMultiset.IsDisjointWith(context.OutputMultiset))
{
//Disjoint so do a Product
initialInput = context.InputMultiset.ProductWithTimeout(context.OutputMultiset, context.RemainingTimeout);
}
else
{
//Normal Join
initialInput = context.InputMultiset.Join(context.OutputMultiset);
}
}
else
{
initialInput = context.OutputMultiset;
}
localOutput = new Multiset();
break;
}
context.InputMultiset = initialInput;
context.OutputMultiset = localOutput;
//Get the Triple Pattern we're evaluating
ITriplePattern temp = this._triplePatterns[pattern];
int resultsFound = 0;
int prevResults = -1;
if (temp is TriplePattern)
{
//Find the first Triple which matches the Pattern
TriplePattern tp = (TriplePattern)temp;
IEnumerable<Triple> ts = tp.GetTriples(context);
//In the case that we're lazily evaluating an optimisable ORDER BY then
//we need to apply OrderBy()'s to our enumeration
//This only applies to the 1st pattern
if (pattern == 0)
{
if (context.Query != null)
{
if (context.Query.OrderBy != null && context.Query.IsOptimisableOrderBy)
{
IComparer<Triple> comparer = context.Query.OrderBy.GetComparer(tp);
if (comparer != null)
{
ts = ts.OrderBy(t => t, comparer);
}
else
{
//Can't get a comparer so can't optimise
this._requiredResults = -1;
}
}
}
}
foreach (Triple t in ts)
{
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
if (tp.Accepts(context, t))
{
resultsFound++;
if (tp.IndexType == TripleIndexType.NoVariables)
{
localOutput = new IdentityMultiset();
context.OutputMultiset = localOutput;
}
else
{
context.OutputMultiset.Add(tp.CreateResult(t));
}
//Recurse unless we're the last pattern
if (pattern < this._triplePatterns.Count - 1)
{
results = this.StreamingEvaluate(context, pattern + 1, out halt);
//If recursion leads to a halt then we halt and return immediately
if (halt && results.Count >= this._requiredResults && this._requiredResults != -1)
{
return results;
}
else if (halt)
{
if (results.Count == 0)
{
//If recursing leads to no results then eliminate all outputs
//Also reset to prevResults to -1
resultsFound = 0;
localOutput = new Multiset();
prevResults = -1;
}
else if (prevResults > -1)
{
if (results.Count == prevResults)
{
//If the amount of results found hasn't increased then this match does not
//generate any further solutions further down the recursion so we can eliminate
//this from the results
localOutput.Remove(localOutput.SetIDs.Max());
}
}
prevResults = results.Count;
//If we're supposed to halt but not reached the number of required results then continue
context.InputMultiset = initialInput;
context.OutputMultiset = localOutput;
}
else
{
//Otherwise we need to keep going here
//So must reset our input and outputs before continuing
context.InputMultiset = initialInput;
context.OutputMultiset = new Multiset();
resultsFound--;
}
}
else
{
//If we're at the last pattern and we've found a match then we can halt
halt = true;
//Generate the final output and return it
if (context.InputMultiset.IsDisjointWith(context.OutputMultiset))
{
//Disjoint so do a Product
results = context.InputMultiset.ProductWithTimeout(context.OutputMultiset, context.RemainingTimeout);
}
else
{
//Normal Join
results = context.InputMultiset.Join(context.OutputMultiset);
}
//If not reached required number of results continue
if (results.Count >= this._requiredResults && this._requiredResults != -1)
{
context.OutputMultiset = results;
return context.OutputMultiset;
}
}
}
}
}
else if (temp is FilterPattern)
{
FilterPattern filter = (FilterPattern)temp;
ISparqlExpression filterExpr = filter.Filter.Expression;
if (filter.Variables.IsDisjoint(context.InputMultiset.Variables))
{
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
//Filter is Disjoint so determine whether it has any affect or not
if (filter.Variables.Any())
{
//Has Variables but disjoint from input => not in scope so gets ignored
//Do we recurse or not?
if (pattern < this._triplePatterns.Count - 1)
{
//Recurse and return
results = this.StreamingEvaluate(context, pattern + 1, out halt);
return results;
}
else
{
//We don't affect the input in any way so just return it
return context.InputMultiset;
}
}
else
{
//No Variables so have to evaluate it to see if it gives true otherwise
try
{
if (filterExpr.Evaluate(context, 0).AsSafeBoolean())
{
if (pattern < this._triplePatterns.Count - 1)
{
//Recurse and return
results = this.StreamingEvaluate(context, pattern + 1, out halt);
return results;
}
else
{
//Last Pattern and we evaluate to true so can return the input as-is
halt = true;
return context.InputMultiset;
}
}
}
catch (RdfQueryException)
{
//Evaluates to false so eliminates all solutions (use an empty Multiset)
return new Multiset();
}
}
}
else
{
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
//Test each solution found so far against the Filter and eliminate those that evalute to false/error
foreach (int id in context.InputMultiset.SetIDs.ToList())
{
try
{
if (filterExpr.Evaluate(context, id).AsSafeBoolean())
{
//If evaluates to true then add to output
context.OutputMultiset.Add(context.InputMultiset[id].Copy());
}
}
catch (RdfQueryException)
{
//Error means we ignore the solution
}
}
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
//Decide whether to recurse or not
resultsFound = context.OutputMultiset.Count;
if (pattern < this._triplePatterns.Count - 1)
{
//Recurse then return
//We can never decide whether to recurse again at this point as we are not capable of deciding
//which solutions should be dumped (that is the job of an earlier pattern in the BGP)
results = this.StreamingEvaluate(context, pattern + 1, out halt);
return results;
}
else
{
halt = true;
//However many results we need we'll halt - previous patterns can call us again if they find more potential solutions
//for us to filter
return context.OutputMultiset;
}
}
}
else if (temp is BindPattern)
{
BindPattern bind = (BindPattern)temp;
ISparqlExpression bindExpr = bind.AssignExpression;
String bindVar = bind.VariableName;
if (context.InputMultiset.ContainsVariable(bindVar))
{
throw new RdfQueryException("Cannot use a BIND assigment to BIND to a variable that has previously been used in the Query");
}
else
{
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
//Compute the Binding for every value
context.OutputMultiset.AddVariable(bindVar);
foreach (ISet s in context.InputMultiset.Sets)
{
ISet x = s.Copy();
try
{
INode val = bindExpr.Evaluate(context, s.ID);
x.Add(bindVar, val);
}
catch (RdfQueryException)
{
//Equivalent to no assignment but the solution is preserved
}
context.OutputMultiset.Add(x.Copy());
}
//Remember to check for Timeouts during Lazy Evaluation
context.CheckTimeout();
//Decide whether to recurse or not
resultsFound = context.OutputMultiset.Count;
if (pattern < this._triplePatterns.Count - 1)
{
//Recurse then return
results = this.StreamingEvaluate(context, pattern + 1, out halt);
return results;
}
else
{
halt = true;
//However many results we need we'll halt - previous patterns can call us again if they find more potential solutions
//for us to extend
return context.OutputMultiset;
}
}
}
else
{
throw new RdfQueryException("Encountered a " + temp.GetType().FullName + " which is not a lazily evaluable Pattern");
}
//If we found no possibles we return the null multiset
if (resultsFound == 0)
{
return new NullMultiset();
}
else
{
//Generate the final output and return it
if (!modifies)
{
if (context.InputMultiset.IsDisjointWith(context.OutputMultiset))
{
//Disjoint so do a Product
results = context.InputMultiset.ProductWithTimeout(context.OutputMultiset, context.RemainingTimeout);
}
else
{
//Normal Join
results = context.InputMultiset.Join(context.OutputMultiset);
}
context.OutputMultiset = results;
}
return context.OutputMultiset;
}
}