rdf:collection in sparql

Question

I have in an RDF file an rdf:collection. When I have a collection of one author the following query returns nothing. However, the query works for two or more authors, but only returns two authors. What can I do to write out all authors?

<bibo:authorList rdf:parseType="Collection">
 <rdf:Description rdf:about="http://openlibrary.org/authors/OL113143A"/>
 <rdf:Description rdf:about="http://openlibrary.org/authors/OL6784959A"/>
</bibo:authorList>

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dc: <http://purl.org/dc/terms/>

select ?title ?author ?author2
where { 
  ?x dc:title ?title . 

  ?x bibo:authorList ?object.
  ?object rdf:first ?name. 
  ?name rdf:value ?author.

  ?object rdf:rest ?object2.
  ?object2 rdf:first ?name2.
  ?name2 rdf:value ?author2 . 
}

Answer 1

Your problem is that you are trying to something semi-recursive so your results vary depending on the length of the RDF list. The query as written will only work for lists of length 2 or more, lists of length 1 won't work due to the fact the second portion of your query will have nothing to match.

If you want to access a collection the best way is with a property path like so (requires SPARQL 1.1):

SELECT * WHERE
{
  ?list rdf:rest*/rdf:first ?member .
}

You can adapt this general pattern to fit into your query as you see fit.