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DC-ARCHITECTURE  March 2007

DC-ARCHITECTURE March 2007

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Subject:

Re: [DCAM Public Comment] abstract syntax needed

From:

"Miles, AJ (Alistair)" <[log in to unmask]>

Reply-To:

DCMI Architecture Forum <[log in to unmask]>

Date:

Mon, 19 Mar 2007 15:40:07 -0000

Content-Type:

text/plain

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> mn 2007-03-19 klockan 10:45 +0000 skrev Miles, AJ (Alistair):
> > Hi Mikael,
> > 
> > > > 
> > > > Of course, as the saying goes, one should put one's foot 
> > > where their 
> > > > mouth is. So I have tried to draft a normative-style 
> document that 
> > > > achieves these goals, with the minimum amount of 
> duplication and 
> > > > unnecessary definition, see:
> > > > 
> > > > 
> > > 
> http://isegserv.itd.rl.ac.uk/cvs-public/~checkout~/dcmi/syntax/index.h
> > > > tm
> > > > l
> > > 
> > > This document contains a number of grave factual errors 
> > > regarding the structure of DCMI descriptions. I do see the 
> > > point, but I *don't* see the big difference between section 
> > > 4-5 and the "description model" of the DCAM...
> > 
> > What are the errors?
> 
> Sorry for the unspecified "grave errors" comment, but here's my issue:
> 
> Except for the restructuring, going from description-centric to
> statement-centric (which I think is mostly a matter of presentation),
> the model is lacking the notions of vocabulary encoding 
> scheme and value
> strings (of which there may be several associated with each value).

You noticed :) ... because they are unnecessary at the syntax level. They can be built into concrete syntaxes as *abbreviations* for multiple statements, but you don't need them in the abstract syntax. 

Compare the way in which the following fragment of Tertle:

ex:foo a ex:Bar; ex:p ex:x, ex:y; ex:q (ex:a ex:b).

... uses abbreviations to provided a compressed representation of the following RDF triples:

ex:foo rdf:type ex:Bar.
ex:foo ex:p ex:x.
ex:foo ex:p ex:y.
ex:foo ex:q _:aaa.
_:aaa rdf:first ex:a.
_:aaa rdf:rest _:bbb.
_:bbb rdf:first ex:b.
_:bbb rdf:rest rdf:nil.

One of the points I'm trying to make in this example is that list constructs are handled in RDF at the *vocabulary level* and not at the *syntax level*. However, various concrete syntaxes (such as Tertle and RDF/XML) do provide convenient abbreviations that hide the complexity of the RDF vocabulary for lists. 

By analogy, DCMI could handle "vocabulary encoding schemes", "syntax encoding schemes" etc. at the *vocabulary level* rather than at the syntax level, which would mean you get a much simpler abstract syntax. Multiple "value strings" can simply be seen as an abbreviation of multiple statements.

Why bother? (a) You get a much more flexible abstract syntax, which would allow you to address the basic concerns of syntactic interoperability without getting tied to definitions of "vocabulary encoding schemes" etc. (b) You get a very simple *syntactic mapping* to RDF, which means you don't need to specify a semantics *at all*. 

N.B. The *only purpose* of a semantics is to define merging procedures and valid inference rules. 

Sorry, best I can do for the moment, I can't think of an easy way to illustrate the point yet.

Cheers,

Alistair.

> 
> /Mikael
> 
> > 
> > Cheers,
> > 
> > Al.
> > 
> > > > 
> > > > [1] http://dublincore.org/documents/2007/02/05/abstract-model/
> > > > [2] http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/
> > > > [3] http://www.w3.org/TR/2004/REC-rdf-mt-20040210/
> > > > --
> > > > Alistair Miles
> > > > Research Associate
> > > > CCLRC - Rutherford Appleton Laboratory Building R1 Room 
> 1.60 Fermi 
> > > > Avenue Chilton Didcot Oxfordshire OX11 0QX United Kingdom
> > > > Web: http://purl.org/net/aliman
> > > > Email: [log in to unmask]
> > > > Tel: +44 (0)1235 445440
> > > > 
> > > --
> > > <[log in to unmask]>
> > > 
> > > Plus a change, plus c'est la mme chose
> > > 
> > 
> -- 
> <[log in to unmask]>
> 
> Plus a change, plus c'est la mme chose
> 

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