Missing triples from PATHS query

[NovasTaylor (Tim Williams)]

Hi Stardog,

I'm running a Stardog 5.2.2 PATHS query over a very simple set of triples that represent the order of "Things". See the attached TTL file.

Each eg:Thing is assigned a type:

eg:Thing1  rdf:type  eg:Thing

When I execute a PATHS query starting at eg:Thing1:

PREFIX eg: <http://www.example.org/myproject#> 
PATHS START ?s = eg:Thing1  
END ?o 
VIA ?p   

it returns the path that includes the rdf:type for that first node. But types for the 2nd node onward are not returned, yet their skos:prefLabel is returned. See attached graph that I create after processing the returned PATHS triples.

I know the rdf:type is in the database because I can SPARQL query for

?s rdf:type eg:Thing

and all 4 entities are returned.

Is there something I am not doing correctly? I find it very curious how rdf:type path is returned for the root node in the path but not in the later nodes.

SequenceTest-AndThen.TTL (663 Bytes)

[stephen]

Hi Tim,

This is happening because of your variable predicate VIA ?p. It’s telling you there’s a path from eg:Thing1 to eg:Thing via rdf:type. The rest of the paths won’t go through that, obviously, since eg:Thing1 doesn’t connect to anything else, but you DO get some paths that go eg:Thing1 -> eg:andThen -> eg:Thing2 -> skos:prefLabel -> “The second thing,” etc.

You’ll likely want to narrow down your VIA a bit, e.g., paths start ?s = eg:Thing1 end ?o via eg:andThen.

If you want to bind rdf:types to your nodes, you can give start/end graph patterns, e.g., paths start ?s = eg:Thing1 end ?o { ?o rdf:type ?oType } via eg:andThen

[NovasTaylor (Tim Williams)]

Sorry, it is still not clear to me. I had thought that the query would return “all triples descendant from eg:Thing1.”

I don’t understand why I get the skos:prefLabel from eg:Thing2, but not the rdf:type.

This path is returned correctly:

eg:Thing1 eg:andThen eg:Thing2 

There are three predicates attached to eg:Thing2. They are: eg:andThen, skos:prefLabel and rdf:type . Only two of these three are returned. I would have expected all three. Instead I get eg:andThen and skos:prefLabel, but not the rdf:type.

eg:Thing2
      rdf:type eg:Thing ;
     skos:prefLabel "The second Thing."^^xsd:string  .

…and later:
eg:Thing2 eg:andThen eg:Thing3 .

[stephen]

Ah, I see what’s going on.

By default, it will return just the shortest path(s) from ?s to ?o, so since it already connected eg:Thing1 to eg:Thing, it doesn’t bother to give you longer ones.

You can run PATHS ALL to get what you’re expecting to see

Edit: paths all start ?s end ?o via ?p I mean

[NovasTaylor (Tim Williams)]

Thanks so much! Clearly an RTFM moment for me. Thanks for your patience. All is working now as it should.