- From: pat hayes <phayes@ai.uwf.edu>
- Date: Mon, 23 Jul 2001 20:55:10 -0700
- To: Brian McBride <bwm@hplb.hpl.hp.com>
- Cc: w3c-rdfcore-wg@w3.org
>Hi Graham, > >Graham Klyne wrote: > > > > > > >#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". > >Loosely in English it means advert123 is for a service that will >buy roses in quantities of at least 100. > > advert123 role buyer >and thereExists ?X advert123 description ?X > ?X product roses > thereExists ?Y ?X minQuantitiy ?Y > ?Y units kg > ?Y minValue 100 That says that it buys roses in a (singular) quantity of at least 100, not ANY (plural) such quantity. It would be made true by a single purchasing act. What you want it to mean is that the service will buy *any* quantity of roses with at least 100 roses in it, but that's not expressible using existential quantifiers. > > > > > There seems to me to be no way of rendering this statement using just > > existential quantification. > >As you see, I've made an attempt. > > > > > 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. > >What is the difference between this and the example in: > > http://lists.w3.org/Archives/Public/www-archive/2001Jun/att-0021/00-part#41 That example refers to a single creator. It doesn't say that http://www.w3.org/Home/Lassila has creator *everything* and they all have name Ora and Email lassila@w3.org. > > > > >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". > >Can you account for the fact that both adverts are very similar in >structure, yet you assign them different semantics? I tend to agree that this should be expressed using a universal as well, given the intended meaning, if it is an assertion. > > > > > 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]. > >This is the essential point. My colleagues believe that if a resource >is not anonymous they will process it differently - i.e. it means >something different. Well, strictly speaking it does mean something different, but its a miniscule difference. Certainly not enough to support any kind of binding to an anonymous node. > > >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. > >I have reread that message and it has not helped me to understand. > >The issue is really very simple. If an anonymous node is used, it means >"a service selling roses in quantities of at least 100". Then that involves a *universally* quantified assertion, not an existential. Think: would this description be satisfied just by a single act of selling less than 100 roses? Or does it assert that *any* such act of selling is on offer here? >If a node with a URI U >is given it means "The service called U selling roses in quantities of least >100". The difference is that a processor of the advert is expected >to know how >to relate U to the service it denotes. At least that's how my colleagues >are using it. Well, we could give RDF that semantics. But if we do, then the example in http://lists.w3.org/Archives/Public/www-archive/2001Jun/att-0021/00-pa rt#41 must mean that *everything* is the creator of http://www.w3.org/Home/Lassila , for example. Pat --------------------------------------------------------------------- (650)859 6569 w (650)494 3973 h (until September) phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
Received on Monday, 23 July 2001 23:55:04 UTC