and of course, the below is for processing an BGP:
@Override
public Op transform(OpBGP opBGP) {
System.out.println("[TransformRemoveOp::transform(OpBGP opBGP)]
opBGPCounter " + opBGPCounter++);
System.out.println("[TransformRemoveOp::transform(OpBGP opBGP)] " +
opBGP.toString());
System.out.println("");
Op newOpBGP = opBGP.copy();
BasicPattern newBP = ((OpBGP) newOpBGP).getPattern();
List<Triple> tripleList = newBP.getList();
Iterator<Triple> itr = tripleList.iterator();
while (itr.hasNext()) {
Triple tp = itr.next();
if (tp.matches(this.triple)) {
itr.remove();
isParent = true;
isStarted = true;
}
}
//...it can be empty
if (((OpBGP) newOpBGP).getPattern().getList().isEmpty()) {
System.out.println("[TransformRemoveOp::transform(OpBGP opBGP)]
opBGP is empty " + opBGP.toString());
//return subOp;
}
return newOpBGP;
}
Many Thanks,
Carlo.
> On 31 Jan 2016, at 04:36, Carlo.Allocca <[email protected]> wrote:
>
> Dear Andy,
>
> Thank you very much one more time.
>
> Please, some comments follow in line.
>
> On 30 Jan 2016, at 17:53, Andy Seaborne
> <[email protected]<mailto:[email protected]>> wrote:
>
> On 30/01/16 15:52, Carlo.Allocca wrote:
> Hello Lorenz,
>
> Thank you for your help.
>
> It was clear to me that I have to remove from the parent expression and such
> is that using a patter-based approach
> make it a bit difficult. I tried three of them and I got to the same results.
>
> You need to process the parent, not just the ElementFilter.
>
> How can I process the parent?
> My understanding is:
>
> 1. Building the Abstract Query Tree: Op op = Algebra.compile(q);
>
> For example, given the query
>
> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
> PREFIX ex: <http://www.semanticweb.org/dataset1/>
> PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
>
> SELECT DISTINCT ?ind ?boss ?g
> WHERE
> { { ?ind rdf:type ?z }
> UNION
> { ?boss ex:isBossOf ?ind
> FILTER ( ?boss = "mathieu" )
> }
> }
>
> I obtain
>
> (distinct
> (project (?ind ?boss ?g)
> (union
> (bgp (triple ?ind <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> ?z))
> (filter (= ?boss "mathieu")
> (bgp (triple ?boss <http://www.semanticweb.org/dataset1/isBossOf>
> ?ind))))))
>
> 2) Travere the tree to modify its internal structure. In terms of code, I can
> write:
>
> (A) Transform transform = new TransformRemoveOp(q,tp) ;
> (B) op = Transformer.transform(transform, op);
>
> where TransformRemoveOp implements Transform interface.
> It seems that there is no link between children and parent that can be used
> to figure out at which level the process is and modify the Tree structure,
> accordingly. Please correct me if I am wrong.
> In fact running it over the above example, I got the following:
>
> =========== DURING
> [TransformRemoveOp::transform(OpBGP opBGP)] opBGPCounter 1
> [TransformRemoveOp::transform(OpBGP opBGP)] (bgp (triple ?ind
> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> ?z))
>
>
> [TransformRemoveOp::transform(OpBGP opBGP)] opBGPCounter 2
> [TransformRemoveOp::transform(OpBGP opBGP)] (bgp (triple ?boss
> <http://www.semanticweb.org/dataset1/isBossOf> ?ind))
>
>
> [TransformRemoveOp::transform(OpBGP opBGP)] opBGP is empty (bgp
> )
>
> [TransformRemoveOp::transform(OpFilter opFilter, Op subOp)] opFilter (filter
> (= ?boss "mathieu")
> (bgp
> ))
>
> [TransformRemoveOp::transform(OpFilter opFilter, Op subOp)] subOp Name bgp
>
> [TransformRemoveOp::transform(OpUnion opUnion, Op left, Op right)] left: (bgp
> (triple ?ind <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> ?z))
>
> [TransformRemoveOp::transform(OpUnion opUnion, Op left, Op right)] right:
> (filter (exprlist (= ?boss "mathieu") true)
> (bgp
> ))
>
>
> [TransformRemoveOp::transform(OpProject opProject, Op subOp)] (project (?ind
> ?boss ?g)
> (union
> (bgp (triple ?ind <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> ?z))
> (filter (exprlist (= ?boss "mathieu") true)
> (bgp
> ))))
>
>
> [TransformRemoveOp::transform(OpDistinct opDistinct, Op subOp)] (distinct
> (project (?ind ?boss ?g)
> (union
> (bgp (triple ?ind <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> ?z))
> (filter (exprlist (= ?boss "mathieu") true)
> (bgp
> )))))
>
>
> Moreover, implementing a first version of the OpFilter as reported below:
>
> @Override
> public Op transform(OpFilter opFilter, Op subOp) {
> System.out.println("[TransformRemoveOp::transform(OpFilter opFilter,
> Op subOp)] opFilter " + opFilter.toString());
> System.out.println("[TransformRemoveOp::transform(OpFilter opFilter,
> Op subOp)] subOp Name " + subOp.getName());
> System.out.println("");
>
> if (isParent == false) {
> return opFilter;
> }
>
> //...get the variables of the triple pattern that we want to delete
> Set<Var> tpVars = new HashSet();
> Node subj = this.triple.getSubject();
> if (subj.isVariable()) {
> tpVars.add((Var) subj);
> }
> Node pred = this.triple.getPredicate();
> if (pred.isVariable()) {
> tpVars.add((Var) pred);
> }
> Node obj = this.triple.getObject();
> if (obj.isVariable()) {
> tpVars.add((Var) obj);
> }
> //...get the variables of the FILTER expression
> Op opNew = opFilter.copy(subOp);
> Set<Var> expVars = ((OpFilter) opNew).getExprs().getVarsMentioned();
>
> //...check whether the FILTER expression contains any of the triple
> pattern variable
> boolean isContained = false;
> for (Var var : expVars) {
> //..if it does then we have to delete the entire FILTER expression
> if (tpVars.contains(var)) {
> isContained = true;
> break;
> }
> }
> //... if the filter contains any variable of the triple that has been
> removed, then....
> if (isContained) {
> Op newOP;
> Expr e;
> if (subOp instanceof OpBGP) {
> if (((OpBGP) subOp).getPattern().getList().isEmpty()) {
> e = new NodeValueBoolean(true);
> newOP = OpFilter.filter(e, opFilter);//filter(e, );
> return newOP;
> } else {
> e = new NodeValueBoolean(false);
> newOP = OpFilter.filter(e, opFilter);//filter(e, );
> return newOP;
> }
> }
> }
> return opFilter;
> }
>
> It produces the following SPARQL query:
>
> SELECT DISTINCT ?ind ?boss ?g
> WHERE
> { { ?ind a ?z }
> UNION
> { # Empty BGP
>
> FILTER ( ?boss = "mathieu" )
> FILTER ( true )
> }
> }
>
> It seems quite challenging even transform the expression of "?boss =
> “mathieu” into “true” (as reported above) does not work as It should.
>
> If anyone could help me who is more experienced with this kind of task, I
> would be very very grateful.
> I would like to see something concrete in sense of line of code as I am using.
>
> Many Thanks,
> Best Regards,
> Carlo
> On 30 Jan 2016, at 17:53, Andy Seaborne
> <[email protected]<mailto:[email protected]>> wrote:
>
> element has active parts
>
> -- The Open University is incorporated by Royal Charter (RC 000391), an
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