Hi Pete,
Yes it does. Again thanks for the clarity.
Cecil E. Somerton
Information Management Analyst | Analyste de gestion de l'information
IM Strategies | Stratégies de la gestion de l'information
Chief Information Officer Branch | Direction du dirigeant principal de l'information
Treasury Board of Canada, Secretariat | Secrétariat du Conseil du Trésor du Canada
Ottawa, Canada K1A 0R5
613 946-5053 | [log in to unmask] | facsimile/télécopieur 613 946-9342
-----Original Message-----
From: DCMI Architecture Group [mailto:[log in to unmask]] On Behalf Of Pete Johnston
Sent: Thursday, June 15, 2006 11:29 AM
To: [log in to unmask]
Subject: Re: RDF/A and DCAPs
Hi Cecil,
> The clarity is very much appreciated. I don't feel
> qualified to engage you in too detailed a discussion but -
> and perhaps naively I understood the challenge with the DC
> and LOM abstract models in DCAPs to be related to the
> capacity of the DCAP to provide a basis for a richer and
> unambiguous semantic to describe and locate a resource. So,
> if the RDF/A provides a richness of semantic description by
> enabling the application of various metadata specifications
> as appropriate to any piece of an XHTML document with an
> unambiguous Namespace reference to the specification's
> abstract model expressed in RFD then to what need a DCAP?
I'm not sure I can really answer your question as I see RDF/A and a DC
Application Profile as rather different things, and I'm not sure my
understanding of what constitutes a DCAP is quite the same as yours ;-)
But I'll have a stab at explaining how I could see them RDFa and a DCAP
maybe fitting together... I should emphasise that I'm not an RDFa adept
- I certainly haven't kept up with the details of the syntax, but I'm
not sure that matters for the purposes of this discussion!
RDFa (as I see from the recent docs it is now called) is a syntax for
representing RDF graphs i.e. RDFa has (more or less) the same
purpose/function as RDF/XML or Turtle or N3 or the various other
syntaxes for RDF. The RDFa syntax has certain characteristics (it's
based on the use of XML attributes - I think that's what the "a" stands
for) which mean it can be embedded in/layered on other XML formats -
nearly all the examples I've seen have been of XHTML 2.0 but I think the
intent is that it is more widely usable, and it could be embedded in
other XML formats too. (I think I've seen this sort of XML
format/language sometimes described as a "parasite language" - which is
quite a nice metaphor: it "lives" on/in a "host" language)
RDFa is based on the RDF "abstract model" i.e. the RDFa syntax is used
to represent subject-predicate-object triples (representing simple
assertions about "the world". X is-created-by Y, P knows Q etc)
DCMI has (or will have, hopefully!) various syntaxes for representing DC
metadata descriptions, e.g. the proposed DC-XML XML format. Other
agencies might also define syntaxes for representing DC metadata
descriptions. Those syntaxes will all be based on the DCMI Abstract
Model: they provide rules for representing in some concrete way the
various constructs described by the DCAM.
The current DC-RDF draft is, arguably, not really a "syntax
specification"; rather, it's a mapping between the DCMI Abstract Model
and the RDF "abstract model".
AFAIK, DCMI still hasn't published a description of what a "DC
Application Profile" really is, in terms of the DCMI Abstract Model.
FWIW, I've worked on the basis of something like: a DCAP is a
specification of the set of terms used, and how they are used, in some
class of DC metadata description sets. i.e. a DCAP tells me for the set
of DC metadata descriptions used within application A or community C or
context D, those description sets contain descriptions of resources of
type X, Y and Z; made with statements using properties P and VES V,
property Q and VES W; statements using property P are required; and so
on. It describes how the DCMI Abstract Model is being used/deployed in
some particular context, if you like. And it probably includes, or
refers to, some sort of description of what that data will enable me or
my application to do (a statement of "functional requirements" for the
DCAP, "what is it for".)
So given a DCAP which I can see is designed to suit my purpose, I can
construct one or more DC metadata description sets in accordance with
that specification (i.e. make staements using property P and VES V and
so on). I could represent/serialise that DC metadata description set
using a suitable syntax e.g. the DC-XML XML format. I could also map it
to the RDF model using the rules in the DC-RDF draft, and then
represent/serialise those RDF graphs using an RDF syntax. I could choose
to use RDF/A for that purpose.
But RDFa just does what it says on the tin: it provides a syntax, a set
of rules for representing my RDF graph using XML attributes. RDFa
doesn't tell me as a metadata creator what URIs I should use in my RDF
graph (or as a metadata consumer what URIs I might expect to find).
Does that help?
Pete
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