Aggregation/Resource Map relationship question - OAI-ORE

Message from discussion Aggregation/Resource Map relationship question
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Message-ID: <303afa280808150242j642bf3fewa232d7ba33c748a1@mail.gmail.com>
Date: Fri, 15 Aug 2008 10:42:26 +0100
From: "Robert Sanderson" <azarot...@gmail.com>
To: oai-ore@googlegroups.com
Subject: Re: Aggregation/Resource Map relationship question
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On Fri, Aug 15, 2008 at 1:49 AM, Jeff Young <jyoung.o...@gmail.com> wrote:

> I can believe that AWWW recognizes the possibility of resources
> without bitstreams, but I will be surprised if it dictates that an RDF
> graph is such a resource. It's difficult to imagine why a set of
> triples can't be a content-negotiable resource.
>

It's not the AWWW that says this, but the fine print in the Named Graph
specification:

"RDF syntax is based on a mathematical abstraction: an RDF graph is defined
as a set of
triples. These graphs are represented by documents which can be retrieved
from URIs
on the Web. Often these URIs are also used as a name for the graph, for
example with
an owl:imports. _____To avoid confusion between these two usages we
distinguish between
Named Graphs and the RDF graph that the Named Graph encodes or
represents._____
A Named Graph is an entity with two functions name and rdfgraph defined on
it which
determine respectively its name, which is a URI , and the RDF graph that it
encodes
or represents. These functions assign a unique name and RDF graph to each
Named
Graph, but Named Graphs may have other properties; and named graphs may be
concrete
resources rather than set-theoretic abstractions." [ __ emphasis added]

However ... Note that the Aggregation is not a Named Graph, it's a subclass
of dcmitypes:Collection.
The Named Graph is the Resource Map.

I agree that a metadata record is a reasonable (summary) representation of
an object, however that's not the model that the AWWW (sometimes rather
clumsily) gives us.  Instead, we have a Collection of Resources (the
Aggregation) which needs an identifier.  We then currently describe that
Collection using a Named Graph called a Resource Map, but there's no reason
that other people couldn't re-use the Aggregation identifier and describe it
with another format.  It would be outside the scope of ORE, but a perfectly
valid re-use of the URI coined for the aggregation.  When we assert
statements about the aggregation, it's the abstract 'work' if you like, not
the specific set of triples which we currently use to describe it.

So, in order to talk about the description in RDF it needs a URI too, URI-R,
which is what makes it a Named Graph rather than just a bunch of triples.
And where better to get a representation of that graph than from its URI!
Thus we have the redirection mechanism, as per AWWW in order to get from the
Aggregation (Collection, Work, Abstract Item of Interest) to the Resource
Map (Description, Named Graph, Concrete Representation)

Does that help?

Rob

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<div dir="ltr"><br><br><div class="gmail_quote">On Fri, Aug 15, 2008 at 1:49 AM, Jeff Young <span dir="ltr">&lt;<a href="mailto:jyoung.o...@gmail.com">jyoung.o...@gmail.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
I can believe that AWWW recognizes the possibility of resources<br>
without bitstreams, but I will be surprised if it dictates that an RDF<br>
graph is such a resource. It&#39;s difficult to imagine why a set of<br>
triples can&#39;t be a content-negotiable resource.<br><div class="Ih2E3d"></div></blockquote><div><br>It&#39;s not the AWWW that says this, but the fine print in the Named Graph specification:<br><br>&quot;RDF syntax is based on a mathematical abstraction: an RDF graph is defined as a set of<br>
triples. These graphs are represented by documents which can be retrieved from URIs<br>on the Web. Often these URIs are also used as a name for the graph, for example with<br>an owl:imports. _____To avoid confusion between these two usages we distinguish between<br>
Named Graphs and the RDF graph that the Named Graph encodes or represents._____<br>A Named Graph is an entity with two functions name and rdfgraph defined on it which<br>determine respectively its name, which is a URI , and the RDF graph that it encodes<br>
or represents. These functions assign a unique name and RDF graph to each Named<br>Graph, but Named Graphs may have other properties; and named graphs may be concrete<br>resources rather than set-theoretic abstractions.&quot; [ __ emphasis added]<br>
<br>However ... Note that the Aggregation is not a Named Graph, it&#39;s a subclass of dcmitypes:Collection.<br>The Named Graph is the Resource Map.<br><br></div></div>I agree that a metadata record is a reasonable (summary) representation of an object, however that&#39;s not the model that the AWWW (sometimes rather clumsily) gives us.&nbsp; Instead, we have a Collection of Resources (the Aggregation) which needs an identifier.&nbsp; We then currently describe that Collection using a Named Graph called a Resource Map, but there&#39;s no reason that other people couldn&#39;t re-use the Aggregation identifier and describe it with another format.&nbsp; It would be outside the scope of ORE, but a perfectly valid re-use of the URI coined for the aggregation.&nbsp; When we assert statements about the aggregation, it&#39;s the abstract &#39;work&#39; if you like, not the specific set of triples which we currently use to describe it.<br>
<br>So, in order to talk about the description in RDF it needs a URI too, URI-R, which is what makes it a Named Graph rather than just a bunch of triples.&nbsp; And where better to get a representation of that graph than from its URI!&nbsp; Thus we have the redirection mechanism, as per AWWW in order to get from the Aggregation (Collection, Work, Abstract Item of Interest) to the Resource Map (Description, Named Graph, Concrete Representation)<br>
<br>Does that help?<br><br>Rob<br><br></div>

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