- From: Jonas Liljegren <jonas@rit.se>
- Date: 20 Nov 2000 15:31:10 +0100
- To: "McBride, Brian" <bwm@hplb.hpl.hp.com>
- Cc: Dan Brickley <danbri@w3.org>, Seth Russell <seth@robustai.net>, RDF-IG <www-rdf-interest@w3.org>
Ok. There have been a bunch of comments on this. I will try to explain my view more clearly. I would like to refere to previous discussion. My post [1] was a reply to Dan Brickley [2] who refered to an entry in the Issue Tracking page [3]. Brian McBride also has some references to earlier discussion [4]. The original discussion, initiated by Dan Brickley [5] is from december 1999. I made the same point also in that discussion [6]. It seems that we have a majority for this view: The statement is the triple. But the reified statement represents a specific stating of a statement. Each stating can have it's own URI. [1] http://lists.w3.org/Archives/Public/www-rdf-interest/2000Nov/0238.html [2] http://lists.w3.org/Archives/Public/www-rdf-interest/2000Nov/0236.html [3] http://www.w3.org/2000/03/rdf-tracking/#rdfms-identity-of-statements [4] http://www-uk.hpl.hp.com/people/bwm/rdf/issues.htm [5] http://lists.w3.org/Archives/Public/www-rdf-interest/1999Dec/0068.html [6] http://lists.w3.org/Archives/Public/www-rdf-interest/1999Dec/0099.html And now the answer to the specific questions: "McBride, Brian" <bwm@hplb.hpl.hp.com> writes: > > Yes. That has been suggested before. But that means that you can't > > use reification in the way examplified in RDF M&S. > > Just to be clear, can you point out the specific examples in M&S that > don't work with the statements as facts interpretation. I don't know what you mean with "the statements as facts interpretation". The question is: Suppose we have two reified statements, S1 and S2. They are both of rdf:type rdf:Statement. They both has the same subject, object and predicate properties. Should S1 and S2 be considered aliases for the same resource? I say 'no'. Here is the example from M&S: <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:a="http://description.org/schema/"> <rdf:Description> <rdf:subject resource="http://www.w3.org/Home/Lassila" /> <rdf:predicate resource="http://description.org/schema/Creator" /> <rdf:object>Ora Lassila</rdf:object> <rdf:type resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement" /> <a:attributedTo>Ralph Swick</a:attributedTo> </rdf:Description> </rdf:RDF> The example uses the property a:attributedTo. You can't attribute an abstract statement to one person. The example view the reified statement as a stating. The reasoning for this is the same as before. Let me repeat the example using This example. Model 1: <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:a="http://description.org/schema/"> <rdf:Description> <rdf:subject resource="http://www.w3.org/Home/Lassila" /> <rdf:predicate resource="http://description.org/schema/Creator" /> <rdf:object>Ora Lassila</rdf:object> <rdf:type resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement" /> <a:attributedTo>Ralph Swick</a:attributedTo> <a:attributedTime>1999-02-22</a:attributedTime> </rdf:Description> </rdf:RDF> Model 2: <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:a="http://description.org/schema/"> <rdf:Description> <rdf:subject resource="http://www.w3.org/Home/Lassila" /> <rdf:predicate resource="http://description.org/schema/Creator" /> <rdf:object>Ora Lassila</rdf:object> <rdf:type resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement" /> <a:attributedTo>Jonas Liljegrenk</a:attributedTo> <a:attributedTime>2000-11-20</a:attributedTime> </rdf:Description> </rdf:RDF> If we import both these models, accepting both as true, and then export them: <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:a="http://description.org/schema/"> <rdf:Description> <rdf:subject resource="http://www.w3.org/Home/Lassila" /> <rdf:predicate resource="http://description.org/schema/Creator" /> <rdf:object>Ora Lassila</rdf:object> <rdf:type resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement" /> <a:attributedTo>Jonas Liljegrenk</a:attributedTo> <a:attributedTo>Ralph Swick</a:attributedTo> <a:attributedTime>1999-02-22</a:attributedTime> <a:attributedTime>2000-11-20</a:attributedTime> </rdf:Description> </rdf:RDF> How do we know which property belongs to which stating? One suggestion to fix this is to create an explicit stating resource: <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:a="http://description.org/schema/"> <rdf:Description ID="S1"> <rdf:subject resource="http://www.w3.org/Home/Lassila" /> <rdf:predicate resource="http://description.org/schema/Creator" /> <rdf:object>Ora Lassila</rdf:object> <rdf:type resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement" /> </rdf:Description> <rdf:Description> <a:states>http://description.org/schema/#S1</a:states> <a:attributedTo>Ralph Swick</a:attributedTo> <a:attributedTime>1999-02-22</a:attributedTime> </rdf:Description> </rdf:RDF> But that's not how the RDF M&S wrote the example, and that's why I wrote "that means that you can't use reification in the way examplified in RDF M&S". > For the record, section 5, the formal model section of M&S states: > > There is a set called Statements, each element of which is a triple > of the form {pred, sub, obj} > > That says that each Statement is a triple of the form (s,p,o). A > triple in mathematics is uniquely determined by its three components. Right. But we can't say the same about the reified statement. There can be many reifications of the same statement. > > My vote is on allowing identical statements with diffrent identities. > > Can you clarify what that sentence means :) How can two identical things > have different identity? If they have different identity, they are not > identical! I was talking about the reifications of the statements. They should be viewed as statings. > > And you can't avoid that with statements distributed over several > > models over the net. > > Different representations of statements. In my world model, statements > are abstract and don't have a location on the net. Perhaps yours is > different. You can give URI's to reified statements. That means that there will be many URIs that have the same predicate, subject and object properites. -- / Jonas Liljegren The Wraf project http://www.uxn.nu/wraf/ Sponsored by http://www.rit.se/
Received on Monday, 20 November 2000 09:33:46 UTC