- From: Seaborne, Andy <andy.seaborne@hp.com>
- Date: Tue, 07 Sep 2004 11:00:28 +0100
- To: Dave Beckett <dave.beckett@bristol.ac.uk>
- CC: RDF Data Access Working Group <public-rdf-dawg@w3.org>
Dave, Thanks for the text. I am including it in the document: For the section 6 text (Choosing What to Query) it is now the draft text. For the section 9 text (SOURCE) I have included it as an alternative to the material Eric wrote. There needs to be a stable version today for the F2F so there may not be time for a considered integration. Eric - We don't loose the text this way. I'm assuming you'll be looking at it. --------- For me, ORIGIN is better than SOURCE (which is ambigous as to whether it is accessing the information or loading it - Alberto's comment) but it suggests the first place a statement was made, not the place an aggregation founf the statement (which itself may be an aggregation). The best I can think of is "GRAPH" (Trix-inspired) which would suggest unification with SimonR's ideas on targeted subqueries (my terminology). "FOUND IN" makes the point but is not nice syntax. FROM seems appropriate - a change of use but it is accurate. Need a replacement for FROM-query-target but that might be easier than a good word for the current SOURCE. Andy Dave Beckett wrote: > I volunteered to own this issue recorded as: > ACTION: DaveB to repropose source in both results and restrictions. > written based on the feedback to my earlier email: > http://lists.w3.org/Archives/Public/public-rdf-dawg/2004JulSep/0307.html > > Refering to > http://www.w3.org/2001/sw/DataAccess/rq23/ > $Revision: 1.52 $ of $Date: 2004/09/03 15:04:38 $ > > I have written for section: > 9. Querying the Origin of Statements > http://www.w3.org/2001/sw/DataAccess/rq23/#source > but I also needed something about data sources so I've got > some additional words for section 6. > > There is also some terminology change compared to the above email, > now using Origin rather than Source to try to distinguish what might > be a DAWG service access point (DAWG protocol API, WSDL1.x portType, > WSDL2 instance of interface, target, file or implicit graph) from a > URI of content. > > Some comments below after the words. > > ---------------------------------------------------------------------- > > 6. Choosing What to Query > > ... > > DAWG queries operate against an RDF graph which is given implicitly > where the graph context is known by the application or known > externally such as by the DAWG protocol. A FROM statement can also > explicitly give a Source URI: > > FROM <http://www.w3.org/2000/08/w3c-synd/home.rss> > SELECT * WHERE > (?x ?y ?z) > > The URI is retrieved and the resulting representation should > represent RDF triples in some syntax, such as RDF/XML which provide > the query graph. > > Aggregate graphs may also be queried by using multiple source URIs in > the FROM clause such as: > > FROM <uri1>, <uri2> > SELECT ... > > However this is implemented, the result must be equivalent to > retrieving the Source URIs and forming the aggregate graph from the > triples returned. Implementations provide a single web service > target that aggregates multiple Source URIs, accessed by the DAWG > protocol or some other mechanism. > > Issue: Refering to the DAWG protocol lots here without checking the > requirements for the protocol match. > > The RDF graph may be constructed through inference rather than > retrieval or never be materialized. > > Issue: Does the use of Source URI and representation for graphs > make sense with this. > > > > 9. Working with the Origin of Triples > [Note change of section title] > > > The Origin of an RDF triple in a query graph is the RDF URI Reference > (ref) where a resource representation was retrieved that provided > that triple, which may be in an aggregate graph. > > Issue: Could allow blank nodes here which would help with the > inferred or non-materialized graphs. > > TRiX http://www.w3.org/2004/03/trix/ removed this after originally > allowing named graphs to be named by blank nodes. I think this was > due to scoping issues. FIXME Find reference to why it was removed. > The ISWC2004 paper? > > A triple in an RDF graph may have zero or more Origins. A BRQL > application may optionally not support recording and providing origin > information. > > Issue: Making origin information optional does not help > interoperability. > > The Origin of a triple may be used in queries with the SOURCE > clause before a triple > > Example 9.1: > Find all triples in an graph of aggregated RSS 1.0 feeds which were > retrieved from the W3C's feed. > > Data: > An aggregated graph of RSS 1.0 feeds including the triples > retrieved from Source URI http://www.w3.org/2000/08/w3c-synd/home.rss > > Query: > SELECT ?x,?y,?z WHERE > SOURCE <http://www.w3.org/2000/08/w3c-synd/home.rss> (?x ?y ?z) > > result: > the RDF triples with origin > <http://www.w3.org/2000/08/w3c-synd/home.rss> > > > If the application does not support origin information or no origin > information was recorded when the aggregated graph was created, no > results are returned. > > Issue: Change to ORIGIN keyword? > > Issue: Make RDF triples become non-RDF quads. > > Origin information can be returned by queries using a variable > with the SOURCE clause. > > Example 9.2 > > An aggregate graph contains aggregated RSS 1.0 feeds and the query > wants to return all items indicating where they were originally > retrieved from, even with duplicates: > > Data: > an aggregate graph of RSS 1.0 feeds > > Query: > SELECT ?s WHERE > SOURCE ?s (?x rdf:type rss:item) > > Results: > ?s= ... ?x=... > for each RSS 1.0 item in the aggregate graph. > > The ?s variables bind to the Origin URIs of the triple that matched. > > If an implementation does not support Origin information, the SOURCE > ?s clause is ignored and no binding value is returned for ?s. > > ?s=null ?x=... > ... > > Issue: this means adding a null value definition which I know is > tricky. The alternate is to not give a result for ?s: > > ?x=... > ... > which means the returned result set is not regular. > > > ---------------------------------------------------------------------- > > My opinion on RDF quads for provenance in queries is well known and > I've discussed this before in depth[1]. I don't like to see them in > RDF query languages since there is little consensus what the fourth > item is - that is one thing we are considering. > > They are of course fine as implementation techniques. What's inside > your application is up to you. > > Dave > > [1] > http://lists.w3.org/Archives/Public/public-rdf-dawg/2004JulSep/0305.html >
Received on Tuesday, 7 September 2004 10:01:51 UTC