/// <summary>
/// Optimises an Algebra to a form that uses <see cref="LazyBgp">LazyBgp</see> where possible
/// </summary>
/// <param name="algebra">Algebra</param>
/// <param name="depth">Depth</param>
/// <returns></returns>
/// <remarks>
/// <para>
/// By transforming a query to use <see cref="LazyBgp">LazyBgp</see> we can achieve much more efficient processing of some forms of queries
/// </para>
/// </remarks>
protected override ISparqlAlgebra OptimiseInternal(ISparqlAlgebra algebra, int depth)
{
try
{
ISparqlAlgebra temp;
//Note this first test is specifically for the default BGP implementation since other optimisers
//may run before us and replace with other BGP implementations which we don't want to replace hence
//why we don't check for IBgp here
if (algebra is Bgp)
{
temp = new LazyBgp(((Bgp)algebra).TriplePatterns);
}
//else if (algebra is ILeftJoin)
//{
// ILeftJoin join = (ILeftJoin)algebra;
// temp = new LeftJoin(this.OptimiseInternal(join.Lhs, depth + 1), join.Rhs, ((LeftJoin)algebra).Filter);
//}
else if (algebra is IUnion)
{
IUnion join = (IUnion)algebra;
temp = new LazyUnion(this.OptimiseInternal(join.Lhs, depth + 1), this.OptimiseInternal(join.Rhs, depth + 1));
}
else if (algebra is IJoin)
{
IJoin join = (IJoin)algebra;
if (join.Lhs.Variables.IsDisjoint(join.Rhs.Variables))
{
//If the sides of the Join are disjoint then can fully transform the join since we only need to find the requisite number of
//solutions on either side to guarantee a product which meets/exceeds the required results
//temp = new Join(this.OptimiseInternal(join.Lhs, depth + 1), this.OptimiseInternal(join.Rhs, depth + 1));
temp = join.Transform(this);
}
else
{
//If the sides are not disjoint then the LHS must be fully evaluated but the RHS need only produce enough
//solutions that match
//temp = new Join(join.Lhs, this.OptimiseInternal(join.Rhs, depth + 1));
temp = join.TransformRhs(this);
}
}
else if (algebra is Algebra.Graph)
{
//Algebra.Graph g = (Algebra.Graph)algebra;
//temp = new Algebra.Graph(this.OptimiseInternal(g.InnerAlgebra, depth + 1), g.GraphSpecifier);
IUnaryOperator op = (IUnaryOperator)algebra;
temp = op.Transform(this);
}
else
{
temp = algebra;
}
return(temp);
}
catch
{
//If the Optimise fails return the current algebra
return(algebra);
}
}
/// <summary>
/// Optimises an Algebra to a form that uses <see cref="AskBgp">AskBgp</see> where possible
/// </summary>
/// <param name="algebra">Algebra</param>
/// <param name="depth">Depth</param>
/// <returns></returns>
/// <remarks>
/// <para>
/// By transforming a query to use <see cref="AskBgp">AskBgp</see> we can achieve much more efficient processing of some forms of queries
/// </para>
/// </remarks>
protected override ISparqlAlgebra OptimiseInternal(ISparqlAlgebra algebra, int depth)
{
try
{
ISparqlAlgebra temp;
if (algebra is Bgp)
{
//Bgp is transformed into AskBgp
//This tries to find 1 possible solution
temp = new AskBgp(((Bgp)algebra).TriplePatterns);
}
else if (algebra is ILeftJoin)
{
//LeftJoin is transformed to just be the LHS as the RHS is irrelevant for ASK queries
//UNLESS the LeftJoin occurs inside a Filter/Minus BUT we should never get called to transform a
//LeftJoin() for those branches of the algebra as the Optimiseer does not transform
//Filter()/Minus() operators
temp = this.OptimiseInternal(((ILeftJoin)algebra).Lhs, depth + 1);
}
else if (algebra is IUnion)
{
IUnion join = (IUnion)algebra;
temp = new AskUnion(this.OptimiseInternal(join.Lhs, depth + 1), this.OptimiseInternal(join.Rhs, depth + 1));
}
else if (algebra is IJoin)
{
IJoin join = (IJoin)algebra;
if (join.Lhs.Variables.IsDisjoint(join.Rhs.Variables))
{
//If the sides of the Join are disjoint then can fully transform the join since we only need to find at least
//one solution on either side in order for the query to match
//temp = new Join(this.OptimiseInternal(join.Lhs, depth + 1), this.OptimiseInternal(join.Rhs, depth + 1));
temp = join.Transform(this);
}
else
{
//If the sides are not disjoint then the LHS must be fully evaluated but the RHS need only produce at least
//one solution based on the full input from the LHS for the query to match
//temp = new Join(join.Lhs, this.OptimiseInternal(join.Rhs, depth + 1));
temp = join.TransformRhs(this);
}
}
else if (algebra is Algebra.Graph)
{
//Algebra.Graph g = (Algebra.Graph)algebra;
//temp = new Algebra.Graph(this.OptimiseInternal(g.InnerAlgebra, depth + 1), g.GraphSpecifier);
IUnaryOperator op = (IUnaryOperator)algebra;
temp = op.Transform(this);
}
else
{
temp = algebra;
}
return(temp);
}
catch
{
//If the Optimise fails return the current algebra
return(algebra);
}
}