RDF Rank is an algorithm that identifies the more important or more popular entities in the repository by examining their interconnectedness. The popularity of entities can then be used to order query results in a similar way to internet search engines, such as how Google orders search results using PageRank http://en.wikipedia.org/wiki/PageRank.
As seen in the example query, RDF Rank weights are made available via a special system predicate. Triple patterns with the predicate http://www.ontotext.com/owlim/RDFRank#hasRDFRank are handled specially by OWLIM, where the object of the statement pattern is bound to a literal containing the RDF Rank of the subject.
To trigger the computation of the RDF Rank values for all resources use the following query:
The full computation of RDF Rank values for all resources can be relatively expensive. When new resources have been added to the repository after a previous full computation of RDF Rank vales, then either a full re-computation can be done for all resources (see above) or only the RDF Rank values for the new resources can be computed (an incremental update). The following control query:
will compute RDF Rank values for those resources that do not have an associated value, i.e. the have been added to the repository since the last RDF Rank computation.
The computed weights can be exported to an external file using a query of this form:
The query will return true if the export was successful, false otherwise. If the export failed then an error message will be recorded in the log file.
Lastly, when using RDF Priming, the RDF Rank values can be used as the initial activation values. To set this up, use the following query:
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