The feature of dlvhex-plugins to be able to rewrite the input program prior to the evaluation opens a variety of powerful application scenarios. Here we demonstrate how dlvhex can be used as a query engine for SPARQL, a W3C candidate for an RDF query language, by providing a rewriter from SPARQL to rules. For more information, see Technical Report GIA-TR-2006-11-28.

Mind that this is a preliminary version for demonstration purposes, which processes only a subset of SPARQL. The supported features are:

1. SELECT queries with simple graph patterns, UNION and OPTIONAL
   

2. N3, RDF/XML, Turtle syntax for input
   

3. Full N3 syntax for triple patterns, including
   

4. ‣blank nodes
   

5. ‣arbitrary nesting of patterns
   

6. Simple conjunctive FILTER expressions:
   

7. ‣conjunction (&&)
   

8. ‣isBound (resp. isBOUND, bound, BOUND)
   

9. ‣isBlank (resp. isBLANK) (purely syntactical and dependend on Raptor)
   

10. ‣binary comparison operators ( =, =<, >=, !=, <, >)
    

11. b-joining and c-joining semantics as defined in the Technical Report GIA-TR-2006-11-28
    

Currently, the limitations are:

1. CONSTRUCT, ASK and DESCRIBE result forms not yet supported.
   

2. Solution modifiers not supported (unlikely they will be in the future, due to their non-declarative aspects)
   

3. FILTERs are still premature and incomplete, e.g. no checks on whether parameters of binops are bound, etc. So far supported are:
   

4. ‣conjunction (&&)
   

5. ‣isBound
   

6. ‣isBlank (purely syntactical and dependend on Raptor)
   

7. ‣binary comparison operators ( =, =<, >=, !=, <, >, translated to DLV native built-ins)
   

8. lack of language-tag awareness or (typed) literals; at the moment, we only allow Qnames, untyped literals, Variables and URIs.
   

9. ‣we don't allow IRI's, i.e. no full unicode support
   

10. ‣we don't allow lang-tags (@) in literals
    

11. ‣we don't allow type datatype tags (^^) in literals
    

12. There is a slight problem with the handling of literals at the moment: the string "foaf:name" cannnot be distinguished in the resulting program from the URI or the QNAME foaf:name most likely!
    

13. Output not yet conforming to SPARQL protocol.
    

You find some examples from the SPARQL Specs at http://con.fusion.at/dlvhex/sparql-query-evaluation.php.