using union in a construct sparql query

Question

hello,

i have such a sparql query:

select ?s ?p ?o from <http://localhost:8890/DAV/ranking&gt; where {
 {<http://seekda.com/providers/cdyne.com/PhoneNotify&gt; so:hasEndpoint ?s.
 ?s ?p ?o} union
 {<http://seekda.com/providers/cdyne.com/PhoneNotify&gt; ?p ?o}
}

but i need a graph query (construct ord describe). unfortunatly i have no clue about how to use unions in construct or describe queries.

please help me best regards simon

Answer 1

The short answer is: there is no difference.

The longer answer is: think about SPARQL queries as having two parts.

1. The query (WHERE) part, which produces a list of variable bindings (although some variables may be unbound).

2. The part which puts together the results. SELECT, ASK, CONSTRUCT, or DESCRIBE.

SELECT * is effectively what the query returns. SELECT ?v1 ?v2 takes results and produces another result set with the other variables removed. ASK just looks to see if there are any results.

CONSTRUCT uses a template to make RDF from the results. For each result row it binds the variables and adds the statements to the result model. If a template triple contains an unbound variable it is skipped.

DESCRIBE is the most unusual, since it takes each result node, finds triples associated with it, and adds them to a result model. Unlike the others it can contain more information than the query matches.

So having UNION, OPTIONAL, whatever, in the query is allowed for all forms. They may lead to missing triples due to unbound variables.

Your query doesn't make much sense. It's no different to {?s ?p ?o}. What are you trying to do? Ok, makes more sense now.

Given clarifications below it sounds like you want the following:

construct { <http://seekda.com/providers/cdyne.com/PhoneNotify&gt; ?p ?o }
from <http://localhost:8890/DAV/ranking&gt; 
where {
  { <http://seekda.com/providers/cdyne.com/PhoneNotify&gt; so:hasEndpoint ?s.
    ?s ?p ?o }
  union
  { <http://seekda.com/providers/cdyne.com/PhoneNotify&gt; ?p ?o }
}