{"id":1817,"date":"2008-01-25T09:18:00","date_gmt":"2008-01-25T09:18:00","guid":{"rendered":"http:\/\/www.leobard.net\/blog\/?p=1817"},"modified":"2017-11-04T15:47:36","modified_gmt":"2017-11-04T15:47:36","slug":"combining-rules-with-sparql","status":"publish","type":"post","link":"https:\/\/www.leobard.net\/blog\/2008\/01\/25\/combining-rules-with-sparql\/","title":{"rendered":"Combining Rules with SPARQL"},"content":{"rendered":"

a recent blog-post by Dan Brickley<\/a> reminded me that we have a Jena-Rule engine augmented with SPARQL dusting our shelves. Its years old, but may be interesting for you.<\/p>\n

We augmented Jena’s rules by adding sparql.
\nThe passing of parameters is easy, you just have to use the variables of the rules. Within Jena rules, you can always express graphs using N-Triple Axioms, so its also possible to write RDF files.
\nOnly caveat: no quads.<\/p>\n

code is in this folder
\nhttp:\/\/gnowsis.opendfki.de\/browser\/tags\/0.8.3-alpha\/gnowsis_retrieval\/WEB-INF\/src\/org\/gnowsis\/retrieval\/RuleQuerySparql.java<\/a><\/p>\n

download SVN URI:
\nhttp:\/\/gnowsis.opendfki.de\/repos\/gnowsis\/tags\/0.8.3-alpha\/gnowsis_retrieval\/WEB-INF\/src\/org\/gnowsis\/retrieval\/RuleQuerySparql.java<\/a><\/p>\n

documentation:
\nhttp:\/\/gnowsis.opendfki.de\/browser\/tags\/0.8.3-alpha\/gnowsis_retrieval\/doc\/help.html<\/a><\/p>\n

Here is a snippet of that documentation for you:<\/p>\n

Inference<\/h2>\n

After the results have been gathered, inference rules are evaluated against the results.
\nThis means, that you can define rules on which new information is generated
\nbased on a declarative syntax described in the
\nJena Rule Engine DOC<\/a>.
\nAn example file for these rules can be found in the source, at best directly in SVN here:
\nretrieval.rules.txt<\/a>.
\nYou can use the existing Jena rules and a special rule that was created by Leo Sauermann to
\nload additional triples from the gnowsis. This query-rule is defined as follows:\n<\/p>\n

\n# Load triples from the search storage by a triple patter.\n# The search storage is crawled by gnowsis IF you enabled it in the\n# configuration and have crawled a few datasources. If not, this query\n# will return nothing.\n\nqueryStorage(?subject, ?predicate, ?object, 'search')\n\n# ?subject, ?predicate, ?object: a triple pattern. \n# Leave one of the empty (= a unbound variable like ?_x) and it will try to match \n# the empty thing as a wildcard. The variables are not bound in the pattern and\n# cannot be used in the same rule. You have to write additional rules to work\n# on the queried triples. \n\nusage example:\n# load all project members and managers\n(?project rdf:type org:Project) ->\nqueryStorage(?project, org:containsMember, ?_y, 'search'),\nqueryStorage(?project, org:managedBy, ?_z, 'search').\n<\/pre>\n
If you want to bind the variables and use them: It is not possible. See the
\nstatement of the Jena developers<\/a> 
\nabout this. But this is not a big problem, you can work around it easily.<\/p>\n
Debugging Inference<\/h2>\n
If you want to tweak your inference rules and don’t want to have gnowsis run the query at all times,
\nyou can use our built-in inference debugging tricks.\n<\/p>\n