How to recursively expand blank nodes in SPARQL construct query?

Question

There is probably an easy to answer to this, but I can't even figure out how to formulate the Google query to find it.

I'm writing SPARQL construct queries against a dataset that includes blank nodes. So if I do a query like

CONSTRUCT {?x ?y ?z .} WHERE {?x ?y ?z .}

Then one of my results might be:

nm:John nm:owns _:Node

Which is a problem if all of the

_:Node nm:has nm:Hats

triples don't also get into the query result somehow (because some parsers I'm using like rdflib for Python really don't like dangling bnodes).

Is there a way to write my original CONSTRUCT query to recursively add all triples attached to any bnode results such that no bnodes are left dangling in my new graph?

Answer 1

Recursion isn't possible. The closest I can think of is SPARQL 1.1 property paths (note: that version is out of date) but bnode tests aren't available (afaik).

You could just remove the statements with trailing bnodes:

CONSTRUCT {?x ?y ?z .} WHERE 
{
  ?x ?y ?z .
  FILTER (!isBlank(?z))
}

or try your luck fetching the next bit:

CONSTRUCT {?x ?y ?z . ?z ?w ?v } WHERE 
{
  ?x ?y ?z .
  OPTIONAL {
    ?z ?w ?v
    FILTER (isBlank(?z) && !isBlank(?v))
  }
}

(that last query is pretty punishing, btw)

You may be better off with DESCRIBE, which will often skip bnodes.