- From: Graham Klyne <Graham.Klyne@Baltimore.com>
- Date: Tue, 17 Jul 2001 16:48:33 +0100
- To: Brian McBride <bwm@hplb.hpl.hp.com>
- Cc: rdf core <w3c-rdfcore-wg@w3.org>
At 08:23 PM 7/16/01 +0100, Brian McBride wrote: >I asked my colleagues if they had any use cases for anon resources >that might help us with this issue. What follows is an (edited) >response I received. > > >Consider the case of describing services and being able to place adverts and >offers for such services. For example here is an (massively simplified) advert >requesting a service (all uri prefixes dropped for clarity): > >#advert123 :role "buyer"; > :description [:product :roses; > :quantity [:units :kg; :minValue "100"]]. What does this RDF actually mean? What statement does it make? I think it's something like: There may exist an X such that: Someone wants to buy X AND There exists a Y such that: X :description Y AND Y :product :roses AND There exists a Z such that: Y :quantity Z AND Z :units :kg AND Z :minValue "100". There seems to me to be no way of rendering this statement using just existential quantification. This may be a compelling use-case, but I don't see any sanction for this usage in M&S 1.0, and as such would suggest it be deferred to V2.0. >And here is a supplier who can offer a range of services: > >#advert456 :role "seller"; > :description [:product :roses; > :quantity [:units :kg; :maxValue "500"]]. I think this case can be expressed adequately using just existential quantification There exists an X such that: X is for sale AND There exists a Y such that: X :description Y AND Y :product :roses AND There exists a Z such that: Y :quantity Z AND Z :units :kg AND Z :maxValue "500". In this case, I think the meaning can be conveyed using either of the approaches we have discussed on the list and in the last teleconference [1]. >Now. If we don't have anonymous nodes then we have the following problems. > >(1) In the seller advert it would appear that the seller is only advertising a >single specific (but under-specified) service, #anon12345 or whatever, which >would be hard to distinguish from an actual service instance like #service42. I would refer to Pat's explanation, copied in [1]. Skolemization seems to work just fine here. >(2) Similarly in the buyer advert instead of describing a template, giving the >service a URI would make it appear that I am looking for a specific >service with >that URI. I still have not heard a argument that this is sanctioned by the current M&S 1.0. If this use-case is to be captured, I think the argument for it needs to be made. >This is clearly similar to DanC's book buying example. Yes, I think so. #g [1] My response to [2], and apparent convergence on two approaches to handling anonymous resources; viz. Skolemization/genid, and scoped variables. http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Jul/0131.html [2] Frank argues that the main goal sanctioned by M&S is statements about resources that exist but which are not named: http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2001Jul/0124.html ------------------------------------------------------------ Graham Klyne Baltimore Technologies Strategic Research Content Security Group <Graham.Klyne@Baltimore.com> <http://www.mimesweeper.com> <http://www.baltimore.com> ------------------------------------------------------------
Received on Tuesday, 17 July 2001 13:08:40 UTC