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Re: ldp-ISSUE-30 (bugtrack): Hierarchical bugtracking service [Use Cases and Requirements]

From: Richard Cyganiak <richard@cyganiak.de>
Date: Tue, 6 Nov 2012 18:50:16 +0000
Cc: public-ldp-wg@w3.org
Message-Id: <B0FD8FB8-B534-49B5-80CA-13E9FCEFBA94@cyganiak.de>
To: Arnaud Le Hors <lehors@us.ibm.com>
On 6 Nov 2012, at 17:01, Arnaud Le Hors wrote:
> > Steve, can't this already be done using the vanilla PATCH/PUT 
> > machinery? It seems all we need is a statement that members MAY be 
> > added and removed to/from containers by means other than POST-to-
> > container and DELETE-member (and DELETE-container).
> 
> Hi Richard, 
> doesn't that make the container a weak aggregator again though?

Let's say that X, Y and Z are resources, and p is a property.

I think the definition of composition, in the context of LDP, is:

  X+p is a composition of Y and Z if there exists triples "X p Y" and
  "X p Z", and deleting X also deletes Y and Z. (Or if deleting X is
  impossible unless Y and Z are deleted first).

I think the definition of (weak) aggregation is:

  X+p is an aggregation of Y and Z if there exists triples "X p Y" and
  "X p Z", and X can be deleted independently from the existence of
  Y and Z.

I think that LDP has made a decision that leads to the following axiom:

  If Y is created by POSTing to X+p, then X+p is a composition, and Y
  becomes a member of the composition.

Now I asked Steve whether adding and removing members of X+p via PUT or PATCH would be sufficient to address the bug tracker use case. You seem to be saying that, if his answer is yes, then that would make X an aggregation. I don't see how this follows from the definitions and axiom above.

I believe that in LDP terminology, containers and compositions are the same thing, while any resource+property combination that is allowed to have more than one value but is not a container is an aggregation.

Best,
Richard
Received on Tuesday, 6 November 2012 18:50:45 UTC

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