Need support for RDF datasets (i.e., graphs, quads)

[TallTed]

Came up in w3c/vc-data-model#1416 (comment)

[afs]

Some thoughts: https://afs.github.io/shacl-datasets.html

[hmottestad]

Here is what we came up with for RDF4J:

[
      a rsx:DataAndShapesGraphLink;
      rsx:shapesGraph <http://example.com/ns#shapesGraph1>;
      rsx:dataGraph ex:dataGraph, ex:dataGraph2;
]

There can be multiple shape graphs and multiple data graphs. The validator will union the shapes graph and parse those, the validate the shapes against the union of the data graphs.

A good thing about this approach is that users can split up their shapes into multiple graphs, then select some of those graphs to validate certain parts of the data. An example could be a ex:relaxedShapesGraph and a ex:strictShapesGraph where some data graphs will need to follow only the relaxed shapes while others need to follow both the strict and the relaxed shapes. A second example could be where there are common vocabularies in separate graphs ex:internalVocabularies and ex:commonVocabularies and we want to validate ex:shapesGraph1 together with the vocabulary graphs, but separate from ex:shapesGraph2.

In RDF4J users have to specify which named graphs can contain shapes. The ShaclSail will only parse shapes from those graphs. This allows users to validate untrusted data without having to worry that the data could contain shapes that would affect the validation. We also then require that any rsx:DataAndShapesGraphLink nodes be the shapes graphs. An rsx:DataAndShapesGraphLink needs to fully reside in a named graph, if it is split between two named graphs then we will ignore it.

https://github.com/eclipse-rdf4j/rdf4j/blob/2306c8b5b3f1d333e1259bb72ea1841b521c9deb/core/sail/shacl/src/test/resources/test-cases/minCount/unionDataset/shacl.trig#L19

[HolgerKnublauch]

@gkellogg I think this is what you were asking for today?

[VladimirAlexiev]

Sveino/Inst4CIM-KG#140 is another user need.

https://github.com/w3c-cg/awesome-semantic-shapes/tree/VladimirAlexiev-patch-1#specifications sec "SHACL on Graphs" lists all approaches that I've heard about:

• Data Graph - The input to a SHACL validator (along with the Shapes Graph or SHACL spec), but these are "ephemeral", and spec doesn't concretize how to pass them to the validator.
• sh:shapesGraph (SHACL spec) - A triple in the data graph that suggests which shapes to select for validation.
• rdf4j:SHACLShapeGraph (RDF4J extension) - default shape graph in RDF4J (see this blog).
• rsx:DataAndShapesGraphLink, rsx:shapesGraph, rsx:dataGraph (RDF4J extension) - describe exactly which shapes go with which graphs (see doc or this blog).
• Extending SHACL to RDF Datasets - Proposal (by Jena's author) that describes one way to apply SHACL to RDF Datasets.

[HolgerKnublauch]

Marking this as postponed as we are beyond the planned work cycle for SHACL Core. We can revisit this if there is renewed time and interest.

[pchampin]

Here is another use-case for named graph support in SHACL :

• passing an RDF dataset instead of an RDF graph as the "data graph"
• only the default graph is considered by the processor by default
• ... unless a property graph with attribute sh:validAgainst is encountered (see below).

If a property shape has a sh:validAgainst attribute, the property shape is satisfied if the value node is the name of a named graph in the dataset, and if that graph is valid against a Shape graphs retrieved from the object of sh:validAgainst.

Below is an example, based on the VC vocabulary. This is a shape graph for a Verifiable Presentation (described in the default graph), which delegates the validation presented credential (described in a named graph) to another shape graph.

:PresentationShape a sh:NodeShape ;
    sh:targetClass vc:VerifiablePresentation ;

    # some constraints on the presentation itself...

    sh:property [
        sh:path vc:verifiableCrendential; # the property relating the VP to the named graph containing the presented credential
        sh:validAgainst <./my-shape-graph-for-credentials.ttl> ;
    ];
.