- From: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
- Date: Wed, 5 May 2004 15:59:40 +0100
- To: RDF Data Access Working Group <public-rdf-dawg@w3.org>
On Tue, May 04, 2004 at 01:45:33 -0700, Rob Shearer wrote: > > "1.8 Derived Graphs > > > > The working group must recognize that RDF graphs are often constructed > > by aggregation from multiple sources and through logical > > inference, and > > that sometimes the graphs are never materialized. Such graphs may be > > arbitrarily large or infinite." > > -- http://www.w3.org/2003/12/swa/dawg-charter#derivedGraphs > > "Logical inference" extends a *lot* farther than just appending triples > to an RDF graph. > There are a lot of ways to say "at least one of these two edges needs to > exist". It can be a consequence of an OWL ontology; it can be a > consequence of a rule encoded in a rules language; it can be a > consequence of any semantic layer you want to put on top of the basic > RDF data model. It does explicitly say something about what RDF graphs > are possible and what are not. But such knowledge does not necessarily > have any sensible encoding in RDF itself. (The best we've seen is > changing the query to little more than "get me the answers" and then > adding triples to the source RDF that say "this is an answer"; an > approach which is both bizarre and quite impractical in the case of more > than one variable which needs to be bound.) This is similar to my concern: If a query includes some extension function (after 3.3), say a function that takes a radius and the URIs for two geo-spatial co-ordinate nodes and returns TRUE if one is in the radius of the other. The complete graph used to answer that query is not neccesarily known to the query engine - especailly if the function is implemented at a lower level. Asking extension functions (for example) to give the triples that it used to answer the question seems unneccesarily onerous. - Steve
Received on Wednesday, 5 May 2004 11:07:07 UTC