/// <summary>
/// Optimises BGPs in the Algebra to use Filter() and Extend() rather than the embedded FILTER and BIND
/// </summary>
/// <param name="algebra">Algebra to optimise</param>
/// <returns></returns>
public ISparqlAlgebra Optimise(ISparqlAlgebra algebra)
{
if (algebra is IAbstractJoin)
{
return ((IAbstractJoin)algebra).Transform(this);
}
else if (algebra is IUnaryOperator)
{
return ((IUnaryOperator)algebra).Transform(this);
}
else if (algebra is IBgp)
{
//Don't integerfer with other optimisers which have added custom BGP implementations
if (!(algebra is Bgp)) return algebra;
IBgp current = (IBgp)algebra;
if (current.PatternCount == 0)
{
return current;
}
else
{
ISparqlAlgebra result = new Bgp();
List<ITriplePattern> patterns = new List<ITriplePattern>();
List<ITriplePattern> ps = new List<ITriplePattern>(current.TriplePatterns.ToList());
for (int i = 0; i < current.PatternCount; i++)
{
//Can't split the BGP if there are Blank Nodes present
if (!ps[i].HasNoBlankVariables) return current;
if (!(ps[i] is TriplePattern))
{
//First ensure that if we've found any other Triple Patterns up to this point
//we dump this into a BGP and join with the result so far
if (patterns.Count > 0)
{
result = Join.CreateJoin(result, new Bgp(patterns));
patterns.Clear();
}
//Then generate the appropriate strict algebra operator
if (ps[i] is FilterPattern)
{
result = new Filter(result, ((FilterPattern)ps[i]).Filter);
}
else if (ps[i] is BindPattern)
{
BindPattern bind = (BindPattern)ps[i];
result = new Extend(result, bind.AssignExpression, bind.VariableName);
}
else if (ps[i] is LetPattern)
{
LetPattern let = (LetPattern)ps[i];
result = new Extend(result, let.AssignExpression, let.VariableName);
}
else if (ps[i] is SubQueryPattern)
{
SubQueryPattern sq = (SubQueryPattern)ps[i];
result = Join.CreateJoin(result, new SubQuery(sq.SubQuery));
}
else if (ps[i] is PropertyPathPattern)
{
PropertyPathPattern pp = (PropertyPathPattern)ps[i];
result = Join.CreateJoin(result, new PropertyPath(pp.Subject, pp.Path, pp.Object));
}
}
else
{
patterns.Add(ps[i]);
}
}
if (patterns.Count == current.PatternCount)
{
//If count of remaining patterns same as original pattern count there was no optimisation
//to do so return as is
return current;
}
else if (patterns.Count > 0)
{
//If any patterns left at end join as a BGP with result so far
result = Join.CreateJoin(result, new Bgp(patterns));
return result;
}
else
{
return result;
}
}
}
else if (algebra is ITerminalOperator)
{
return algebra;
}
else
{
return algebra;
}
}
/// <summary>
/// Optimises BGPs in the Algebra to use Filter() and Extend() rather than the embedded FILTER and BIND
/// </summary>
/// <param name="algebra">Algebra to optimise</param>
/// <returns></returns>
public ISparqlAlgebra Optimise(ISparqlAlgebra algebra)
{
if (algebra is IAbstractJoin)
{
return ((IAbstractJoin)algebra).Transform(this);
}
else if (algebra is IUnaryOperator)
{
return ((IUnaryOperator)algebra).Transform(this);
}
else if (algebra is IBgp)
{
IBgp current = (IBgp)algebra;
if (current.PatternCount == 0)
{
return current;
}
else
{
ISparqlAlgebra result = new Bgp();
List<ITriplePattern> patterns = new List<ITriplePattern>();
List<ITriplePattern> ps = new List<ITriplePattern>(current.TriplePatterns.ToList());
for (int i = 0; i < current.PatternCount; i++)
{
if (ps[i] is FilterPattern || ps[i] is BindPattern)
{
//First ensure that if we've found any other Triple Patterns up to this point
//we dump this into a BGP and join with the result so far
if (patterns.Count > 0)
{
result = Join.CreateJoin(result, new Bgp(patterns));
patterns.Clear();
}
if (ps[i] is FilterPattern)
{
result = new Filter(result, ((FilterPattern)ps[i]).Filter);
}
else
{
BindPattern bind = (BindPattern)ps[i];
result = new Extend(result, bind.AssignExpression, bind.VariableName);
}
}
else
{
patterns.Add(ps[i]);
}
}
if (patterns.Count == current.PatternCount)
{
//If count of remaining patterns same as original pattern count there was no optimisation
//to do so return as is
return current;
}
else if (patterns.Count > 0)
{
//If any patterns left at end join as a BGP with result so far
result = Join.CreateJoin(result, new Bgp(patterns));
return result;
}
else
{
return result;
}
}
}
else if (algebra is ITerminalOperator)
{
return algebra;
}
else
{
return algebra;
}
}
