Hey Andy, I have another question about comparing ElementPathBlock's the way you suggest below using IsoMatcher.
The following two graph patterns should (in my opinion and for my use case) not be the same, but the IsoMatcher says they match: graphpattern1: ?a <http://www.tno.nl/test1> ?b . ?b <http://www.tno.nl/test2> ?a . graphpattern2: ?a <http://www.tno.nl/test1> ?b . ?a <http://www.tno.nl/test2> ?b . Since RDF triples form a directed graph, this result surprises me, because in graphpattern1 the subject of /test1 has a single outgoing edge, while in graphpattern2 the subject of /test1 has two outgoing edges. How can this be judged the same? I've tested it in two ways: - converting all variables to blank nodes and using: IsoMatcher match = new IsoMatcher(tuplesTriples(gr1.find()), tuplesTriples(gr2.find()), new ResultSetCompare.BNodeIso(NodeUtils.sameValue)); - or not converting them to blank nodes and using: IsoMatcher match = new IsoMatcher(tuplesTriples(gr1.find()), tuplesTriples(gr2.find()), new CustomBNodeIso(NodeUtils.sameValue)); Where CustomBNodeIso adds the IF statement you suggest below. In both cases the above two graph patterns are judged the same while they shouldn't. Any idea what I'm doing wrong? Regards, Barry -----Original Message----- From: Nouwt, B. (Barry) <[email protected]> Sent: donderdag 21 november 2019 13:03 To: [email protected] Subject: RE: ElementPathBlock comparison Hey Andy, thanks. I'm currently testing the IsoMatcher - EqualityTest combination and the first tests look promising. I use the following code (where the gr1 and gr2 graphs have all variables of the graph pattern replaced by blanknodes): IsoMatcher match = new IsoMatcher(tuplesTriples(gr1.find()), tuplesTriples(gr2.find()), new ResultSetCompare.BNodeIso(NodeUtils.sameValue)); but as I said, it requires some more testing. Not having to convert the variable into blanknodes would probably be more elegant, so maybe I'll try your suggestion below as well. Regards, Barry -----Original Message----- From: Andy Seaborne <[email protected]> Sent: woensdag 20 november 2019 10:41 To: [email protected] Subject: Re: ElementPathBlock comparison On 19/11/2019 15:52, Nouwt, B. (Barry) wrote: > Hi Andy, I have an additional question regarding your tip about turning > variables into blanknodes with names; would that also work in case of > predicates? Because variables can be located at the 'predicate' location of a > triple, but I'm unsure whether blanknodes are allowed at that location. Yes. My recommendation is to write a EqualityTest that does variable isomorphism. It's a small chnage to the Copy BNodeIso and add the "if": if ( n1.isVariable() && n2.isVariable() ) return mapping.makeIsomorphic(n1, n2) ; (not tested) Andy > > Regards, Barry > > -----Original Message----- > From: Nouwt, B. (Barry) <[email protected]> > Sent: dinsdag 19 november 2019 16:49 > To: [email protected] > Subject: RE: ElementPathBlock comparison > > Thanks for the quick replies. > > @Andy Exactly, I do care about the shape, but not about exact variable names. > > I wanted to use Google Guava Graph library to construct the graphs and use > their equality mechanism, but I think the IsoMatcher is a better fit, thanks > for the pointer! This together with your tip about transforming the same > variable nodes into blank nodes with the same name, it might just work in > combination with BNodeIso. I'll give that a try and report back the result. > > BTW In the comments of this IsoMatcher class, it says "For graphs, the Graph > isomorphism code in Jena is much better (better tested, better performance)", > is this relevant for me? And do you know which isomorphism code in Jena is it > referring to? > > @Martynas I could, indeed, encode the two BGPs into two RDF graphs using > sp:TriplePattern, but then I still a way to match them. For my problem this > RDF encoding is not necessary and encoding it using the Google Guava Graph > lib seems sufficient. > > Regards, Barry > > -----Original Message----- > From: Andy Seaborne <[email protected]> > Sent: dinsdag 19 november 2019 15:49 > To: [email protected] > Subject: Re: ElementPathBlock comparison > > >> Hi all, >> >> I have two ARQ ElementPathBlocks (or Basic Graph Pattern, see SPARQL spec >> https://www.w3.org/TR/sparql11-query/#GraphPattern) and would like to know >> whether they are equal ignoring variable names and ordering of the triples. >> What is the best/easiest way to do that with the Apache Jena? I see there is >> an org.apache.jena.sparql.util.Iso class that provides methods for testing >> isomorphisms...but I'm unsure whether this is what I am looking for. I also >> tested two ElementPathBlocks and using their equalTo method (which uses the >> Iso class), but both variable names and order seems to matter judging them >> equal. > > I'm guessing you mean not caring about the variable names but respecting the > shape they create in the BGP. > > IsoMatcher is a simple algorithm for matching unordered lists > (Iso.isomorphic is ordered lists.) > > If you want to ignore variables names you'll need a "EqualityTest" > that captures that > > > BNodeIso does this for bnodes. Modifying that for a Var->Var map > loosk possible (or converting the input BGPs to have a bnode with > label derived from the Variable name). > > Andy > This message may contain information that is not intended for you. If you are > not the addressee or if this message was sent to you by mistake, you are > requested to inform the sender and delete the message. TNO accepts no > liability for the content of this e-mail, for the manner in which you use it > and for damage of any kind resulting from the risks inherent to the > electronic transmission of messages. >
