Hello Carlo,
you have to remove the whole filter from it's parent expression, which
makes it a little bit more difficult in a visitor pattern-based
implementation. But should be rather simple, just some lines of code.
Lorenz
Dear Andy and all,
Thank yo very much for your help to accomplish this task.
I am using the package org.apache.jena.sparql.syntax as suggested.
The way I am doing it is the following:
===== MAIN CLASS
// This is the main method to implement the remove of a triple from a SPARQL
query
private static Query RemoveOpImplementation(Query q, Triple tp) {
Op op = Algebra.compile(q);
Transform transform = new TransformRemoveOp(q,tp) ;
op = Transformer.transform(transform, op) ;
Query queryWithoutTriplePattern = OpAsQuery.asQuery(op) ;
}
===== TransformRemoveOp
// the implement the transform
public class TransformRemoveOp implements Transform {
}
Again, removing the triple is quite straightforward
@Override
public Op transform(OpBGP opBGP) {
System.out.println("[TransformRemoveOp::transform(OpBGP opBGP)] " +
opBGP.toString());
System.out.println("");
Op opNew = opBGP.copy();
BasicPattern newBP = ((OpBGP) opNew).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();
}
}
return opNew;
}
but not the Filter
@Override
public Op transform(OpFilter opFilter, Op subOp) {
//...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
for (Var var : expVars) {
//..if it does then we have to delete the entire FILTER expression
if (tpVars.contains(var)) {
System.out.println("[TransformRemoveOp::transform(OpFilter
opFilter, Op subOp)] FILTER TO BE REMOVED!!!HOW? ");
System.out.println("");
}
}
return opFilter;
}
Sorry for posting again and again the same question.
What am I missing or not understanding?
How should I use the abstract syntax tree to do it?
I am looking at the code of the example reported in Jena, but still I am
strangling to find it out.
Please, any example code that I could have look at?
Many Thanks in advance for your help and support.
Best Regards,
Carlo
On 29 Jan 2016, at 14:16, Andy Seaborne
<a...@apache.org<mailto:a...@apache.org>> wrote:
On 29/01/16 12:57, Carlo.Allocca wrote:
Dear Andy and All,
I tried to use as many suggested info as I could. As result, I obtained the
following:
I am implementing a public class RemoveOpTransform implements ElementTransform.
And, again It is quite straightforward to remove the triple pattern from the
ElementPathBlock
@Override
public Element transform(ElementPathBlock eltPB) {
The idea of the transform design is to not change the inoput but to create a
new copy if you change it. If you don't change it you can return the input.
System.out.println("[RemoveOpTransform::transform(ElementPathBlock arg0)]
" + eltPB.toString());
Iterator<TriplePath> l = eltPB.patternElts();
while (l.hasNext()) {
TriplePath tp = l.next();
if (tp.asTriple().matches(this.triple)) {
l.remove();
System.out.println("[RemoveOpTransform::transform(ElementPathBlock
arg0)] TRIPLE MAP JUST REMOVED!!! ");
System.out.println("");
return this.transform(eltPB);//eltPB;
}
}
return eltPB;
}
But I could not figure out how to remove the associated FILTER when
transform(ElementFilter arg0, Expr arg1) as below
To remove a filter altogether you need to delete the ElementFilter object from
the AST (abstract syntax tree). You can't do that inside the
transform/ElementFilter.
It means looking in the element containing the ElementFilter which will be in a
ElementGroup of some kind, probably as part of an ElementUnion.
An alternative is to replace the filter expression with a no-op like
FILTER(true)
and live with that.
Andy
@Override
public Element transform(ElementFilter arg0, Expr arg1) {
//...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
Set<Var> expVars = arg1.getVarsMentioned();
//...check whether the FILTER expression contains any of the triple
pattern variable
for (Var var : expVars) {
//..if it does then we have to delete the entire FILTER expression
if (tpVars.contains(var)) {
System.out.println("[SQRemoveTripleVisitor::visit(ElementFilter
arg0)] FILTER TO BE REMOVED!!!HOW? ");
System.out.println("");
}
}
return arg0;
}
It appears to me that I am at the same point of the previous approach.
What am I doing wrong or missing? Or what I should ready to figure it out?
Thank you very much for your kind help and support.
Best Regards,
Carlo
On 29 Jan 2016, at 10:32, Andy Seaborne
<a...@apache.org<mailto:a...@apache.org>> wrote:
You'll still have to clean up structures. SPIN for this is encoding the query
in RDF but the rewriting of that structure needs the same (in the abstract)
processing. You may be able to do it with a series of SPARQL Updates (that's
speculation).
Andy
On 29/01/16 00:26, Carlo.Allocca wrote:
Dear Martynas,
Thank you very much for your help.
At the moment, I am trying what Andy suggested.
I hope to make it. Otherwise, I will look at SPIN API.
Many Thanks,
Best Regards,
Carlo
On 28 Jan 2016, at 23:48, Martynas Jusevičius
<marty...@graphity.org<mailto:marty...@graphity.org>> wrote:
You could do it using SPIN API as well: http://spinrdf.org/sp.html
On Thu, Jan 28, 2016 at 7:39 PM, Carlo.Allocca
<carlo.allo...@open.ac.uk<mailto:carlo.allo...@open.ac.uk>> wrote:
Dear Andy,
Thank you very much for your promtly reply.
I need a little bit of exploring and thinking to apply what you suggested.
Indeed, I will look at each single info you pointed out.
I will keep this thread updated.
Many Thanks,
Best Regards,
Carlo
On 28 Jan 2016, at 18:29, Andy Seaborne
<a...@apache.org<mailto:a...@apache.org>> wrote:
The approach I would take is to do this is multiple passes:
1/ remove from ElementPathBlock
2/ Look for elements that are now "empty"
e.g ElementFilter with empty
but also as there one arm of a UNION.
(2) is only one pass as the rewrite is done bottom up.
I would do this as a transformation rather than modifying the syntax tree in
place.
org.apache.jena.sparql.syntax.syntaxtransform
See also
ElementTransformCleanGroupsOfOne
which might be helpful to understand - its doing something different though.
It might be easier to work on the algebra, it's more regular. Then use
OpAsQuery to turn algebnra into a Query.
I could not figure out how to remove the associated FILTER
when visit(ElementFilter el) as below.
because you need to alter the ElementUnion which holds the ElementFilter.
{...} UNION {} will include a blank row for the {} on the right hand side.
Andy
On 28/01/16 13:14, Carlo.Allocca wrote:
Dear All,
I am using Jena for my project and I would like to submit the following
question: How to remove consistently a triple pattern given a SPARQL query?
EXAMPLE:
For example, considering the query “qString1” and the tp=“?boss ex:isBossOf
?ind .”
I need to remove tp from qString1, obtaining qString1. For “Consistently” I
mean that the clause FILTER gets affected (as it contains var that appears in
the triple pattern too), therefore it needs to be deleted too.
String qString1 =
" SELECT DISTINCT ?ind ?boss ?g where "
+ "{ "
+ " ?ind rdf:type ex:AssociatedResearcher ."
+ " {?ind rdf:type ?z. } UNION "
+ " {?boss ex:isBossOf ?ind . Filter(?boss=\”rossi\”)} "
+ "}";
String qString2 =
" SELECT DISTINCT ?ind ?boss ?g “
+ “WHERE "
+ "{ "
+ " ?ind rdf:type ex:AssociatedResearcher ."
+ " {?ind rdf:type ?z. } UNION "
+ " {} "
+ "}";
The solution that I am trying to implement is based on a visitor
“SQRemoveTripleVisitor extends ElementVisitorBase”.
It is quite straightforward to remove the triple pattern when
visit(ElementPathBlock el)
@Override
public void visit(ElementPathBlock el) {
if (el == null) {
throw new
IllegalStateException("[SQRemoveTripleVisitor::visit(ElementPathBlock el)] The
ElementPathBlock is null!!");
}
ListIterator<TriplePath> it = el.getPattern().iterator();
while (it.hasNext()) {
final TriplePath tp1 = it.next();
if (this.tp != null) {
if (this.tp.matches(tp1.asTriple())) {
it.remove();
}
}
}
}
I could not figure out how to remove the associated FILTER when
visit(ElementFilter el) as below.
@Override
public void visit(ElementFilter el) {
//...get the variables of the FILTER expression
Expr filterExp = el.getExpr();//.getVarsMentioned().contains(el);
Set<Var> expVars = filterExp.getVarsMentioned();
//...get the variables of the triple pattern that we want to delete
Set<Var> tpVars = new HashSet();
Node subj = this.tp.getSubject();
if (subj.isVariable()) {
tpVars.add((Var) subj);
}
Node pred = this.tp.getPredicate();
if (pred.isVariable()) {
tpVars.add((Var) pred);
}
Node obj = this.tp.getObject();
if (obj.isVariable()) {
tpVars.add((Var) obj);
}
//...check whether the FILTER expression contains any of the triple
pattern’s variable
for(Var var:expVars){
//…if it does then we have to delete the entire FILTER expression
if(tpVars.contains(var)){
System.out.println("[SQRemoveTripleVisitor::visit(ElementFilter el)]
I NEED TO REMOVE THE FILTER!!!!!! ");
}
}
}
Please, may I ask for any help or idea on how to remove the filter?
Many Thanks in advance.
Best Regards,
Carlo
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Lorenz Bühmann
AKSW group, University of Leipzig
Group: http://aksw.org - semantic web research center
