OWLIM-SE has special support for 2-dimensional geo-spatial data that uses the WGS84 Geo Positioning RDF vocabulary (World Geodetic System 1984). Special indices can be used for this data that permit the efficient evaluation of special query forms and extension functions that allow:
The WGS84 ontology can be found at: http://www.w3.org/2003/01/geo/wgs84_pos and contains several classes and predicates:
Before the geo-spatial extensions can be used, the geo-spatial index must be built. This is achieved by inserting and committing a dummy statement (that is not actually stored) that uses a special predicate:
If the indexing is successful, the above update will succeed, otherwise an exception will be thrown. Information about the indexing process and any errors can be found in the log. Note that this update will fail if there is no geo-spatial data in the repository, i.e. no statements describing resources with latitude and longitude properties.
The special syntax used to query geo-spatial data makes use of SPARQL's RDF Collections syntax. This syntax uses round brackets as a shorthand for the statements connecting a list of values using rdf:first and rdf:rest predicates with terminating rdf:nil. Statement patterns that use one of the special geo-spatial predicates supported by OWLIM-SE are treated differently by the query engine. The following special syntax is supported when evaluating SPARQL queries (the descriptions all use the namespace:
At present there is just one SPARQL extension function.
Knowledge of the implementation's algorithms and assumptions will allow users to make the best use of the OWLIM-SE geo-spatial extensions. The following points are significant and can affect the expected behaviour during query answering:
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