W3C home > Mailing lists > Public > w3c-rdfcore-wg@w3.org > June 2002

RE: Outline for new RDF document

From: pat hayes <phayes@ai.uwf.edu>
Date: Fri, 28 Jun 2002 01:04:08 -0500
Message-Id: <p05111b29b941aae7203e@[]>
To: "Jeremy Carroll" <jjc@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org

>  > >The main content is to do with vocabulary, particularly:
>>  >- containers
>>  >- reification
>>  >- rdf:value
>>  >
>>  >I understand that we are maintaining M&S containers but without formal
>>  >semantic support and hence somewhere we need informal but normative
>>  I do not understand what that is supposed to mean, and would strongly
>>  suggest that we do not make any informal text normative. If we wish
>>  to make some aspect of containers normative, then lets put that
>>  aspect into the model theory, which is the normative account of RDF
>>  meaning. The reason there is no formal semantic support for the M&S
>>  text on containers is because that text is simply incoherent: the
>>  intent that it expresses *cannot* be rendered in RDF, for essentially
>>  logical reasons. Rdf:Bags *cannot possibly* be bags. It seems to me
>>  to be a serious error to put into the spec as a normative passage
>>  something that is provably impossible given the rest of the spec.
>My concern re containers is that the following normative text from 
>M&S is not in
>our new specs in a normative fashion.
>(P90) RDF defines three types of container objects:
>Bag An unordered list of resources or literals. Bags are used to 
>declare that a
>property has multiple values and that there is no significance to the order in
>which the values are given. Bag might be used to give a list of part numbers
>where the order of processing the parts does not matter. Duplicate values are
>Sequence An ordered list of resources or literals. Sequence is used to declare
>that a property has multiple values and that the order of the values is
>significant. Sequence might be used, for example, to preserve an alphabetical
>ordering of values. Duplicate values are permitted.
>Alternative   A list of resources or literals that represent alternatives for
>the (single) value of a property. Alternative might be used to provide
>alternative language translations for the title of a work, or to 
>provide a list
>of Internet mirror sites at which a resource might be found. An application
>using a property whose value is an Alternative collection is aware that it can
>choose any one of the items in the list as appropriate.
>We have chosen not to try and formally express this.

Well, not exactly. We tried to formally express it (the Bag part) and 
discovered that it didn't really make sense. That is, the items in a 
bag are in a fixed order in RDF, and there's just no way of getting 
around that. We should be careful not to give the opposite impression 
in the text.

>That does not mean that people should not and will not use rdf:Bag, 
>rdf:Seq and
>rdf:Alt according to this usage.
>It is not sufficient to merely state this in the primer.
>It could be in schema, but the schema editor seems to have ducked.
>I would be happy with text like para 90 (above) in either the new doc, schema,
>or even model theory;

Im quite willing to have text along these 'intended meanings' lines 
in the MT, with appropriate caveats about entailments. In fact I 
think that is where it should go, so as to avoid any impression that 
the different parts of the spec are disagreeing with one another. Of 
course it can go somewhere else as well :-)

>and then explanatory examples in the primer.


>Similarly with reification the intended use as being about triples in RDF
>documents was normative and in my mind still is normative. All that we have
>agreed to clairfy is that we are talking statings and not statements and any
>suggested equality between rdf:Statements with the same subject, predicate and
>object in M&S was a mistake.
>So on reification once again I think a paragraph or two stating this intended
>usage, as normative, is justified. Once again I don't care where it goes.

OK, similar remarks to above. I think the latest draft of the MT does 
have prose like this in it, in fact: maybe it needs expanding some.

>>  PS:  Just to head off this answer, I don't think a idea like "the new
>  > document has informal but normative text while the Primer has
>>  non-normative text" is a reasonable distinction to make if there is
>>  going to be a lot of overlap in the coverage of the two documents, since
>>  that would leave us with a given issue being covered by text that is
>>  [formal,normative], [informal,normative], and [informal,non-normative],
>>  which sounds a tad dangerous.  I thought the reason why people wanted
>>  the Primer to be non-normative in the first place was because the text
>>  was informal.
>I think you have understood my position, and we currently disagree :(
>I am quite happy to have all the examples in the primer.
>I think the other possible path is to reopen the postponed issues to do with
>containers. I think we postponed them because fixing containers 
>would do serious
>damage to M&S and hence take us out of charter.

Lets not go there, I agree. But then lets also not *pretend* we have 
gone there when we havn't, I guess is my chief concern.


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Received on Friday, 28 June 2002 02:04:08 UTC

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