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Re: Data Flow

From: Mark Baker <distobj@acm.org>
Date: Tue, 14 Oct 2003 13:24:25 -0400
To: algermissen@acm.org
Cc: www-ws@w3.org
Message-ID: <20031014132425.A28387@www.markbaker.ca>

Hi Jan,

On Sat, Oct 11, 2003 at 06:14:37AM -0400, Jan Algermissen wrote:
> > FWIW, using a RESTful approach to composition seems to simplify things
> > greatly.  As each resource is a potential data source (via its state),
> > this enables composition to be described with containment relations.
> > For example, a description of the pipe "A | B" might be;
> > 
> > <Container rdf:about="B">
> >   <contains/>
> >     <Container rdf:about="A"/>
> > </Container>
> > 
> > That doesn't say who does the binding, i.e. whether B invoked GET on A,
> > or A invoked POST on B, or even if C invoked GET on A and POST on B ...
> > but the flow (aka route) is the same in all those cases.
> 
> This is very interesting. What I don't quite understand is how the
> containment relates to the pipe? Is your thinking that, for example'
> a POST to A results in a subsequent POST to B?

That information isn't available in that example.

If we wanted to add it, we could define a "Filter" class (as a subclass
of Container);

 <Container rdf:about="B">
   <contains/>
     <Filter rdf:about="A"/>
 </Container>

or perhaps this, if we wanted to specify that the stream was a
representation of a single resource;

 <Filter rdf:about="B">
   <contains/>
     <Filter rdf:about="A"/>
 </Filter>

This is probably more in line with what I understand "data flow" to
mean in this discussion, so thanks for asking.

> Hmm, or would a change in A's state imply a change in B's state since
> B contains A?

I don't think so.

> IOW, what is the relationship between resource-resource containment and
> resource state? 

None, I'd say.

> Is it defined anywhere what containment of resource in resource means/implies?

In that example, I meant for it to mean the same as aggregation by
reference in UML.

> Wonder how that relates to the "nested containers" discussion[1]
> (e.g. what are the implications for list items to be contained in
> lists)?

I'd say that's a more general form of containment.  For example, it
could be used to describe aggregation by value.

> Anyhow, just vague thoughts.... 

Ditto. 8-)

Mark.
-- 
Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
Received on Tuesday, 14 October 2003 13:19:29 GMT

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