LARQ = Lucene + ARQ

SPARQL is normally thought of as only querying fixed RDF data. At the core of SPARQL are the building blocks of basic graph patterns, and on top of these there is an algebra to create more complex patterns (OPTIONAL UNION, FILTER, GRAPH).

The key question a basic graph pattern asks is "does this pattern match the graph". The named variables record how the pattern matches.

Not all information needs to be in the raw data. ARQ property functions are a way to let the application add some relationships to be computed at query execution time.

LARQ adds free text search. The real work is done by Lucene. LARQ adds ways to create a Lucene index from RDF data and a property function to perform free text matching in a SPARQL query.

Example: find all the string literals that match '+keyword'

PREFIX pf: <java:com.hp.hpl.jena.query.pfunction.library.>

SELECT *
  { ?lit pf:textMatch '+keyword' }

Any simple or complex Lucene query string can be used.

LARQ provides utilities to index string literals. As the literal can be stored as well, a query can find the subjects with some property value matching the free text search.

So to find all the document that have titles matching some free text search:

PREFIX pf: <java:com.hp.hpl.jena.query.pfunction.library.>
PREFIX dc: <http://purl.org/dc/elements/1.1/>
  
SELECT ?doc {
    ?lit pf:textMatch '+text' .
    ?doc ?p ?lit
  }

More details in the ARQ documentation for LARQ

This will be in ARQ 1.5 but is available from ARQ CVS now. Hopefully, this will be useful to users and application writers. Comments and feedback on the design are welcome, especially before the next ARQ release.