On 9 Dec 2010, at 17:53, Diogo FC Patrao wrote: > For instance, is it GAV ou LAV? The mapping file describes how one global > schema concept (a class, or a property) maps to the database, with all JOINs > and WHEREs needed to do that. I think that makes it GAV, but that's me > thinking.
It's GAV. To the extent that this terminology is applicable in RDF land. A lot of data integration literature takes the relational model and its “schema first, data second” for granted, and unfortunately just doesn't parse in the “data first, schema second” world of RDF. An often cited downside of GAV is that one needs to revise all the mappings whenever one adds a source. In the easiest case, this means changing “SELECT * FROM source1.table UNION SELECT * FROM source 2.table” to “SELECT * FROM source1.table UNION SELECT * FROM source 2.table UNION SELECT * FROM source3.table” for each table in the schema. In RDF, one doesn't need to do such a revision because one essentially just spills more triples into the big graph. In the absence of a strict schema, the distinction between LAV and GAV is quite meaningless. Or so I think -- I'd love to read a good theoretical treatment of this topic! I'm not aware of any unfortunately. > Another doubt is about answering SPARQL queries - is it query rewriting? or > query answering? I guess the first one, by the kind of SQL queries it > generates. It certainly does query rewriting, in the data integration sense. Maybe it *also* does query answering -- depends on your definition of that term. > Is there any paper that describes the theoretical grounds for d2rq? I wish! Best, Richard > > > * for instance, "D2R MAP – A Database to RDF Mapping Language Christian Bizer" > > Diogo F.C. Patrão > Manager of Medical Informatics > Biotechnology Laboratory > Hospital A.C. Camargo > http://www.accamargo.org.br/ > ------------------------------------------------------------------------------ > _______________________________________________ > d2rq-map-devel mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/d2rq-map-devel ------------------------------------------------------------------------------ Learn how Oracle Real Application Clusters (RAC) One Node allows customers to consolidate database storage, standardize their database environment, and, should the need arise, upgrade to a full multi-node Oracle RAC database without downtime or disruption http://p.sf.net/sfu/oracle-sfdevnl _______________________________________________ d2rq-map-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/d2rq-map-devel
