How to get notified of changes to RDF4J.SHACL_SHAPE_GRAPH through ShaclSailConnection

[mperry455]

Hi,

We're trying to get notifications for statements added to the RDF4J.SHACL_SHAPE_GRAPH context, but various listeners are not doing the trick.

We're using RDF4J 4.2.1

The code below gives notifications if we do not add anything to RDF4J.SHACL_SHAPE_GRAPH:

    ShaclSail shaclSail = new ShaclSail(new MemoryStore());
    Repository rep = new SailRepository(shaclSail);
    rep.init();
    try (SailRepositoryConnection conn = (SailRepositoryConnection) rep.getConnection()) {
        NotifyingSailConnection sailConn = (NotifyingSailConnection) conn.getSailConnection();
        NotifyingSailConnection wrappedConn = ((NotifyingSailConnectionWrapper)sailConn).getWrappedConnection();
        wrappedConn.addConnectionListener(new SailConnectionListener() {

            @Override
            public void statementRemoved(Statement removed) {
                System.out.println("removed: " + removed);
            }

            @Override
            public void statementAdded(Statement added) {
                System.out.println("added: " + added);
            }
        });

        conn.begin();
        conn.add(FOAF.PERSON, RDF.TYPE, RDFS.CLASS, RDF4J.SHACL_SHAPE_GRAPH);
        String update = "DELETE { ?p a rdfs:Class } INSERT { ?p rdfs:label \"Person\" } WHERE { ?p a rdfs:Class }";
        conn.prepareUpdate(update).execute();
        System.out.println("executed");
        conn.commit();
        conn.rollback();
        System.out.println("transaction aborted");
    }

Output:

added: (http://xmlns.com/foaf/0.1/Person, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2000/01/rdf-schema#Class)
removed: (http://xmlns.com/foaf/0.1/Person, http://www.w3.org/1999/02/22-rdf-syntax-ns#type, http://www.w3.org/2000/01/rdf-schema#Class) [null]
added: (http://xmlns.com/foaf/0.1/Person, http://www.w3.org/2000/01/rdf-schema#label, "Person")
executed
transaction aborted

As soon as we touch RDF4J.SHACL_SHAPE_GRAPH the notifications go away:

    ShaclSail shaclSail = new ShaclSail(new MemoryStore());
    Repository rep = new SailRepository(shaclSail);
    rep.init();
    try (SailRepositoryConnection conn = (SailRepositoryConnection) rep.getConnection()) {
        NotifyingSailConnection sailConn = (NotifyingSailConnection) conn.getSailConnection();
        NotifyingSailConnection wrappedConn = ((NotifyingSailConnectionWrapper)sailConn).getWrappedConnection();
        wrappedConn.addConnectionListener(new SailConnectionListener() {

            @Override
            public void statementRemoved(Statement removed) {
                System.out.println("removed: " + removed);
            }

            @Override
            public void statementAdded(Statement added) {
                System.out.println("added: " + added);
            }
        });

        conn.begin();
        conn.add(FOAF.PERSON, RDF.TYPE, RDFS.CLASS, RDF4J.SHACL_SHAPE_GRAPH);
        String update = "DELETE { ?p a rdfs:Class } INSERT { ?p rdfs:label \"Person\" } WHERE { ?p a rdfs:Class }";
        conn.prepareUpdate(update).execute();
        System.out.println("executed");
        conn.commit();
        conn.rollback();
        System.out.println("transaction aborted");
    }

Output:

executed
transaction aborted

Is there a way to get notified of changes to RDF4J_SHACL_SHAPE graph?

Thanks.

[hmottestad]

It's stored in a separate MemoryStore, which is why you're not receiving notifications.

It might be possible to do something to allow you to attach to the MemoryStore, but I don't think there's anything possible right now.

What's your use case btw?

[mperry455]

Thanks for the info.

With regards to the use case, we are trying to support ShaclSail on top of our Sail implementation. We found that certain constraints, for example sh:and, are implemented as a multi-step process where all target nodes are first read into memory. This was causing some performance issues, so we wanted to catch the use of such constraints to raise a warning or error to avoid validations that don't finish in a reasonable time.

[hmottestad]

We could probably add the connection listener to the MemoryStoreConnection used for storing the shapes. I hadn't really thought to do it. We wouldn't be able to do it until 5.1.0 or 5.2.0.

Another, maybe simpler way, is to extend the ShaclSail and override the getConnection() method. Have it return your own CustomShaclSailConnection (which extend the ShaclSailConnection) and override the two addStatement(...) methods, the two removeStatement(...) methods and the clear(...) method.

[mperry455]

Thanks for the suggestion. We were actually looking extending ShaclSail and overriding getConnection() to add a listener to the ShaclSailConnection. Overriding getConnection() to return a wrapper around the ShaclSailConnection with overridden addStatement() methods seems to work. Do you see any issues with the approach below?

  public class MyShaclSail extends ShaclSail {
    public MyShaclSail(NotifyingSail baseSail) {
      super(baseSail);
    }
    
    @Override
    public NotifyingSailConnection getConnection() throws SailException {
        return new MyShaclSailConnection(super.getConnection());
    }
  }
  
  public class MyShaclSailConnection extends NotifyingSailConnectionWrapper {

    public MyShaclSailConnection(NotifyingSailConnection wrappedCon) {
      super(wrappedCon);
    }
    
    @Override
    public void addStatement(Resource subj, IRI pred, Value obj, Resource... contexts) throws SailException {
      System.out.println("Adding Statement ["+subj.toString()+" "+pred.toString()+" "+obj.toString()+"]");
      this.getWrappedConnection().addStatement(subj, pred, obj, contexts);
    }
    
    @Override
    public void addStatement(UpdateContext modify, Resource subj, IRI pred, Value obj, Resource... contexts)
            throws SailException {
      System.out.println("Adding Statement ["+subj.toString()+" "+pred.toString()+" "+obj.toString()+"]");
      this.getWrappedConnection().addStatement(modify, subj, pred, obj, contexts);
    }
  }

[hmottestad]

Looks good. If all you're doing is logging a warning it should be fine, but keep in mind that statements can be removed afterwards in the same transaction.

Shapes can be added to other graphs than just the RDF4J SHACL Shapes Graph. For them to be detected those graphs need to be added to the config. My point is just that you probably want to be liberal with when you choose to log your warning.

[mperry455]

Got it. Thanks again for the help.