Aggregation/Resource Map relationship question - OAI-ORE

Message from discussion Aggregation/Resource Map relationship question
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Date: Fri, 15 Aug 2008 17:09:24 -0700 (PDT)
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Subject: Re: Aggregation/Resource Map relationship question
From: Jeff Young <jyoung.o...@gmail.com>
To: OAI-ORE <oai-ore@googlegroups.com>
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Thanks Herbert, I'll add these to my reading list.

Jeff

On Aug 15, 6:28=A0pm, Herbert Van de Sompel <hvds...@gmail.com> wrote:
> Jeff
>
> We are following the directions given in the W3C "Cool URIs for the =A0
> semantic web" document when it comes to e.g. the HTTP 303 from uri-a =A0
> to uri-r. And the same approaches listed there are also promoted in =A0
> the Linked Data effort.
>
> Herbert
>
> Sent from my iPhone
>
> On Aug 15, 2008, at 14:06, Jeff Young <jyoung.o...@gmail.com> wrote:
>
>
>
> > On Aug 15, 5:42 am, "Robert Sanderson" <azarot...@gmail.com> wrote:
> >> It's not the AWWW that says this, but the fine print in the Named =A0
> >> Graph
> >> specification:
>
> >> "RDF syntax is based on a mathematical abstraction: an RDF graph is =
=A0
> >> defined
> >> as a set of
> >> triples. These graphs are represented by documents which can be =A0
> >> retrieved
> >> from URIs
> >> on the Web. Often these URIs are also used as a name for the graph, =
=A0
> >> 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._____
>
> > I'll add the Named Graph document to AWWW on my reading list. It
> > worries me that I have to dig so deep, though, to understand why
> > HTTP's resource/representation model isn't adequate here. The
> > confusion being referred to is presumably caused by the fact that in
> > HTTP representations are typically resources in their own right. They
> > seem to be saying that people can't tell the difference and therefore
> > RDF needs to invent a competing model to clarify the problem.
>
> > In fact, HTTP already provides a generalized mechanism to clarify this
> > difference: the 300 (Multiple Choices) status. The big missing piece
> > is a specification for the response body, which can be community-
> > specific and even RDF-enriched. In reverse, the best mechanism for
> > tracing backward from representation to resource is still unclear to
> > me, but this problem doesn't seem so overwhelming that I would be
> > happy to chuck HTTP's generalized resource/representation model in
> > favor of the Named Graphs model.
>
> >> A Named Graph is an entity with two functions name and rdfgraph =A0
> >> defined on
> >> it which
> >> determine respectively its name, which is a URI , and the RDF graph =
=A0
> >> that it
> >> encodes
> >> or represents. These functions assign a unique name and RDF graph =A0
> >> to each
> >> Named
> >> Graph, but Named Graphs may have other properties; and named graphs =
=A0
> >> may be
> >> concrete
> >> resources rather than set-theoretic abstractions." [ __ emphasis =A0
> >> added]
>
> > As far as I know, anything can be a resource according to HTTP. Does
> > RDF disagree with this liberalism? Perhaps the Named Graph authors
> > want to define "set-theoretic abstractions" as a class of "entities"
> > that isn't allowed to be represented in HTTP as a resource?
>
> >> However ... Note that the Aggregation is not a Named Graph, it's a =A0
> >> subclass
> >> of dcmitypes:Collection.
> >> The Named Graph is the Resource Map.
>
> > I'm not doubting that these are separate resources. What I doubt is
> > the need to say "An Aggregation does not have a representation". Why
> > can't the Resource Map be accepted as a representation of the
> > aggregation? It's already returning it in response to the
> > Aggregation's URI. It's disconcerting to have an Aggregation URI that
> > is "without a representation" respond on demand with something that is
> > indistinguishable from a representation. Where is the line drawn
> > between what is allowed to be a representation, and what isn't? I'm
> > pretty sure it isn't defined in HTTP. RDF doesn't assume the HTTP data
> > model, so it can't be there. Is it the Named Graph authors? Is it ORE?
>
> > If you believe me that the limits of representations are arbitrary,
> > why not allow the Aggregation URI to return other types of responses
> > according to content-negotiation principles? Is ORE's concept of
> > Aggregations limited to its particular use cases, or does it extend
> > beyond into reality itself? Why be greedy here?
>
> > Sorry, but I need to stop here for now. My brain is fried.
>
> > Jeff
>
> >> I agree that a metadata record is a reasonable (summary) =A0
> >> representation of
> >> an object, however that's not the model that the AWWW (sometimes =A0
> >> rather
> >> clumsily) gives us. =A0Instead, we have a Collection of Resources (the
> >> Aggregation) which needs an identifier. =A0We then currently describe =
=A0
> >> that
> >> Collection using a Named Graph called a Resource Map, but there's =A0
> >> no reason
> >> that other people couldn't re-use the Aggregation identifier and =A0
> >> describe it
> >> with another format. =A0It would be outside the scope of ORE, but a =
=A0
> >> perfectly
> >> valid re-use of the URI coined for the aggregation. =A0When we assert
> >> statements about the aggregation, it's the abstract 'work' if you =A0
> >> 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 =A0
> >> too, URI-R,
> >> which is what makes it a Named Graph rather than just a bunch of =A0
> >> triples.
> >> And where better to get a representation of that graph than from =A0
> >> its URI!
> >> Thus we have the redirection mechanism, as per AWWW in order to get =
=A0
> >> from the
> >> Aggregation (Collection, Work, Abstract Item of Interest) to the =A0
> >> Resource
> >> Map (Description, Named Graph, Concrete Representation)
>
> >> Does that help?
>