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RE: Sample schema extension models

From: Butler, Mark <Mark_Butler@hplb.hpl.hp.com>
Date: Fri, 6 Jun 2003 11:48:42 +0100
Message-ID: <5E13A1874524D411A876006008CD059F066A1D2B@0-mail-1.hpl.hp.com>
To: "'Jason Kinner'" <jason_kinner@dynamicdigitalmedia.com>, www-rdf-dspace@w3.org

Hi Jason

Okay, I've been thinking this through, and I understand it a bit better now.
One approach that helped is the one John Sowa uses in Knowledge
Representation i.e. converting the graphs into English sentences. I actually
find this pretty helpful, so if we apply this to the first proposal we get
(the numbers are for reference later)

1. There exists a Created called urn1 that precedes Situation urn3,
hasAction urn2 and hasPatient hdl:1234/123.

2. There exists a Create Action called urn2 that creates hdl:1234/123

3. There exists a Situation called urn3.

4. There exists a Modified Action called urn4 that follows Situation urn3,
precedes Situation urn5 and hasPatient hdl:1234/123

5. There exists a Situation called urn5.

6. There exists an Item called hdl:1234/123;1, inContext urn3, with title
"My Example" which is a phaseOf hdl:1234/123

7. There exists an Item called hdl:1234/123;2, inContext urn5, with title
"Our Example" which is a phaseOf hdl:1234/123

where

hasPatient is a subProperty of involves

So before I couldn't see the point of urn3 and urn5 as they contain no
information apart from their type, but I had overlooked the inContext
property of hdl:1234/123;1 and hdl:1234/123;2. So that makes sense now.
However I'm still confused about why we need sentences 1 and 2 - can't we
combine them into a single sentence e.g.

1.5 There exists a Create Action called urn1 that precedes situation urn3,
that creates hdl:1234/123

i.e. that is more similar to sentence 4? Why are sentences 1 and 2 different
to 4?

Also I'm afraid I've got to pick on some of your terminology ... 

> I'll grant you that there is complexity, but I feel it is a 
> valid model.
> The need for Situations is that they represent the resting state of a
> portion of the model (the existential facet) /between/ events.  

Lagoze et al use the term existential facet, but I don't like it - "facet"
has a very specific meaning in the library community - for example see
http://www.getty.edu/research/tools/vocabulary/aat/about.html

Lagoze's definition is "From the perspective of first-order logic, the
existential facet corresponds to there exists a situation in which an
instance of the entity exists with a property set and the universal facet
corresponds to for all situations in the description the entity exists with
a certain property set."

So the "existential facet" is their approach to implementing contexts. 

> Events
> and Actions represent the kinetic portion of the model, 

I don't believe the model has a kinetic portion, that's a term you would use
when talking about oscillatory systems. Better: "Events and Actions
represent the processes and Situations represent the contexts"?

thanks,

Dr Mark H. Butler
Research Scientist                HP Labs Bristol
mark-h_butler@hp.com
Internet: http://www-uk.hpl.hp.com/people/marbut/
Received on Friday, 6 June 2003 06:49:07 EDT

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