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Different senses of specialization

From: James Cheney <jcheney@inf.ed.ac.uk>
Date: Mon, 9 Apr 2012 15:57:55 +0100
Message-Id: <6E41929F-271B-4B67-8DA4-60073F471F98@inf.ed.ac.uk>
To: ProvenanceWorking Group WG <public-prov-wg@w3.org>

In reading the discussion over the last week and while reviewing the various documents, I've noticed that "specialization" seems to be being used in (at least) three different ways.  I think this is a contributor to the confusion concerning specialization and alternate. 

specializationOf_1: To express when one entity provides a more specific description of the same thing as another entity.  

Example: The entity ex:article in the primer, with its versions ex:articleV1 and ex:articleV2, both of which are specializations of ex:article.

This is the sense that I have been assuming and it is what is reflected in the semantics.

specializationOf_2: To express when one entity provides more specific information than another (which need not be about the same thing!)


specializationOf(customerInChairAt6pm, customerInChair)
specializationOf(customerInChairAt7pm, customerInChair)

To me this does not make sense because the entities customerInChairAt6pm and customerInChairAt7pm are about different "Things" (the different customers Alice and Bob).  So there is no single Thing to which customerInChair describes, contradicting (what I thought was) the consensus that an entity describes an aspect of exactly one thing.

In my view, this sense of specialization is specious, since one entity may provide "more specific" information than another entity but the two entities need not be about the same thing, as the relationship may be purely coincidental.  To carry this to an extreme, any entity is a "specializationOf(2)

specializationOf_3: (work / item) To express when one entity describes a more concrete thing that is an instance of a more abstract thing described by another entity.  This is like the work/item distinction in FRBR.

Example: The primer refers to a file (which can have multiple versions), and a specific copy of a file on  a hard disk, as another example of specialization.  

To me this does not make sense because a file, in the abstract, is just a sequence of bits, which could be physically realized anywhere or could be realized in multiple places at once.  A file-on-disk might carry the same information as an abstract-file, but can only exist in one place.  We do not talk about locations explicitly in PROV, but even so, I think this is confusing: again, to carry the argument to an extreme, the number 2, in the abstract, is not the same kind of thing as a piece of paper with "two" written on it.

I think specializationOf_3 ("instance/realization of") is a sensible notion, but it should not be conflated with specializationOf_1.  There are already vocabularies that deal with this type of relationship, such as FRBR itself.  If we believe that PROV should attempt to solve this in a new way, I think we should avoid overloading the notion of specialization as "different, more specific information about the same thing" with this notion, which is really about "more concrete instance of an abstract thing"

To summarize:
- I think we should be careful about these different senses of "specializationOf". 
- Only the first sense is supported by the current version of the semantics.
- If we can agree on one of these definitions for specializationOf, but believe other senses need to be modeled, we should introduce additional relations to name them, and ensure that the meanings are clear and they are used consistently in examples.

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Received on Monday, 9 April 2012 14:58:35 UTC

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