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RE: containers: primer material

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Tue, 16 Apr 2002 15:44:36 +0100
To: "Frank Manola" <fmanola@mitre.org>, "RDF Core" <w3c-rdfcore-wg@w3.org>
Message-ID: <JAEBJCLMIFLKLOJGMELDAEKMCDAA.jjc@hplb.hpl.hp.com>
>
> 1.  can I legally create a container resource (say, a Bag) without using
> any special syntax, simply by using the ordinary RDF/XML techniques for
> creating a blank node, and giving it the appropriate properties
> (including the type property pointing to the pre-defined rdf:Bag
> resource, and the various li (or explicit _number) properties)?

Yes - this is the point of the resolution along time ago of

rdf-containers-syntax-vs-schema

>
> 2.  can I also legally create a container resource that has a URI (i.e.,
> that *isn't* a blank node), by using the ordinary RDF/XML techniques for
> creating a new resource with an ID, and giving it those same appropriate
> properties (e.g., a type property pointing to one of the pre-defined
> container type resources)?

Yes

>
> Note 1:  since the above involves essentially the "manual" creation of
> container resources, if this is legit, ought we to have a constraint
> that says that the same container can't have multiple rdf:type
> properties that have inconsistent values (like the same container being
> both a bag and an alt;  on the other hand, how would we enforce it?)


It is not inconsistent (said with a straight face!).

A Bag indicates that here is a container with possibly multiple repeat
entries (i.e. a multiset)
Applications may wish to read Bags with conjunctive semantics

An Alt indicates that here is a container with possibly multiple repeat
entries (i.e. a multiset). The first element is distinguished (value of
rdf:_1).
Applciations may wish to read Alt with disjunctive semantics.

Seq indicates that here is a container with possibly multiple repeat entries
(i.e. a multiset). The elements of the container are ordered.

Something that is both a Bag and an Alt is from the RDF Model Theory point
of view just fine. From an application point of view, sometimes a
disjunctive reading should be taken sometimes a conjunctive reading - not
particularly helpful, but possible.

We have decided not to formalise these differences. I am assuming the
normative text like that in M&S that states these things informally will go
into the model theory. Such text will leave open issue like is

<rdf:Seq rdf:_1="a" rdf:_2="b"/>

intended as the same as or different from

<rdf:Seq rdf:_3="a" rdf:_4="b"/>

(at the model theory level these are clearly different).

> Also, please don't refer
> me to prior RDF Core documented resolutions on containers.  I've read
> them, and can't figure out what they mean

I understood the WG decision to close #rdf-containers-otherapproaches as a
decision to not clarify these questions.


Jeremy
Received on Tuesday, 16 April 2002 10:47:54 EDT

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