RE: [topicmaps-comment] occurences and modeling resources

[Kal Ahmed <kal@techquila.com>]

At 15:09 18/12/2001 -0500, Howard Goldberg wrote:

> > -----Original Message-----
> > From: Lars Marius Garshol [mailto:larsga@garshol.priv.no]
> > Sent: Tuesday, December 18, 2001 1:54 PM
> > To: topicmaps-comment@lists.oasis-open.org
> > Subject: Re: [topicmaps-comment] occurences and modeling resources
> >
> >
> >
> > * Howard Goldberg
> > |
> > | 1.  In the conceptual model, an occurence is uniquely identified by
> > | an instanceOf, a scope, and a resourceRef.  Therefore, it appears
> > | that any occurrence that shares the same tuple should have the same
> > | occurence identifier.
> >
> > If two occurrences of the same topic have the same values for these
> > properties (as well as for the <resourceData>, if they have any) they
> > need to be replaced by a single occurrence. (XTM 1.0, annex F.2.6.)
> > I am not sure if this is what you are thinking of, however.
> >
> > This is not the same as saying that the identity of an occurrence
> > object in the internals of a topic map engine is necessarily
> > determined by these four values. There is no rigorous specification of
> > what is required here, nor do I think that there should be.
> >
> > What you mean by "occurrence identifier" I don't know. Could you
> > explain? Your question seems to be about this identifier, so it sounds
> > important.
> >
> > | For example, if I have multiple topics that each appear in the
> > | english version of my home page, each occurence in every topic
> > | shares the same identifier, and are reified by one topic whose
> > | subjectIndicatorRef is that single occurence identifier.
> >
> > Here it seems that you are making a common mistake: the resource
> > referred to by this occurrence is *not* the same as the occurrence.
> > The resource is just the resource, while the occurrence represents the
> > relationship between the resource and the topic.
>
>
>In the example of 3.9.1 of xtm 1.0 (<occurence> Element)
>
><topic id="hamlet">
>. . .
>         <occurrence id="hamlet-in-xml">
>                 <instanceOf> ...</instanceOf>
>                 <resourceRef xlink= ". . .>
>         </occurrence>
></topic>
>
>and the occurrence is reified by
>
><topic id="hamlet-in-xml-topic">
>         <subjectIdentity>
>                 <subjectIndicatorRef xlink:href="#hamlet-in-xml">
>         </subjectIdentity>
>. . .
>
>If I create topic2 with the same occurrence as topic hamlet, are the
>occurrence id's the same in both topics, or does topic2 have a unique
>occurence id and the reified occurrence have multiple subjectIndicatorRefs?
>
><topic id="topic2">
>. . .
>         <occurrence id="hamlet-in-xml">
>         [same elements as above] . . .
></topic>
>
>or
>
><topic id="topic2">
>. . .
>         <occurrence id="topic2-in-xml">
>         [same elements as above] . . .
></topic>
>
><topic id="hamlet-in-xml-topic">
>         <subjectIdentity>
>                 <subjectIndicatorRef xlink:href="#hamlet-in-xml">
>                 <subjectIndicatorRef xlink:href="#topic2-in-xml">
>         </subjectIdentity>
>. . .
>

Although you could do this, I have a suspicion that it is not modelling 
what you expect it to model. In the example immediately above, you are 
asserting that the two occurrences are indicators of the same subject. I 
suspect that what you want to do is actually to reify the *resource* and 
not the occurrence(s). If this is the case, then you can simply use the 
resource URL as the subject indicator of the reifying topic and you are 
done - the topic will "automatically" reify that resource independently of 
the topics of which it is an occurrence.

So, here are three possible modelling options, each of which has a 
different end-result:

1) If you want to name a resource or add meta-data to a resource, or make 
any other assertion about that specific resource in your topic map, reify 
the resource itself, by creating a topic which specifies the resource URL 
as its <subject>.

2) If you want to make an assertion about the subject described by a 
resource, reify the subject of the resource by creation a topic which 
specifies the resource URL as one of its <subjectIndicator>'s

3) If you want to make some assertions about a specific topic-to-resource 
relationship, reify the occurrence 'subject', by creating a topic which 
specifies the URL of the <occurrence> element as one of it's 
<subjectIndicator>'s

Cheers,

Kal