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Re: bags of axioms

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 31 Oct 2007 17:02:51 -0500
Message-Id: <p06230922c34ea9545ff2@[]>
To: Matthew Pocock <matthew.pocock@ncl.ac.uk>
Cc: public-owl-dev@w3.org

>We've started moving quite sizeable amounts of OWL 1.1 xml about via web
>services. We're currently doing this by pushing an OWL:Ontology element
>inside the SOAP body. We are having problems with the 'semantics' of the
>ontology element itself, and by extension, how the tools we are using handle
>ontologies as data-structures.


>Through having logical and physical URIs, the ontology elements are making
>some sort of statement that they are a recognisable set of axioms, that exist
>for some purpose, and so on.

? Why? This seems like wrong thinking to me. First, there's no 
distinction between 'logical and physical' URIs, so lets just talk 
about URIs. Think of a URI as a name. Giving a name to something is 
just making a statement that it can be referred to, is all. And that 
hardly amounts to saying anything about it. Google queries are 
evanescent things that have no location, but they are encoded as URIs.

>The axioms we are moving about are either
>sub-sets of the axioms within an ontology with a known logical URI, or are a
>sub-set of the entailment of the axioms within an ontology with a known
>logical URI.


>They are not in themsevles a cohesive whole of axioms, but
>rather more like incremental updates, deltas.

But they are sets, right? So they are, for example, RDF graphs if 
written in OWL/RDF.

>  In particular, it makes no
>sense at all to give them a physical URI.

You mean, I think, a URI that anyone would expect to be able to 
resolve with HTTP GET to retrieve the set of axioms. OK.

>The role fulfilled by the logical
>URI for 'real' ontologies is also somewhat moot in this context - what
>defines the bag of axioms in our case is the original ontology, and the
>assertion that these are a (possibly arbitrary) sub-set of the entailment of
>that ontology, possibly with extra information defining bounds on what made
>it into the sub-set.

All they have to be is a set of axioms, in order to be a well-formed ontology.

>Our system allows a certain amount of slop in what gets
>passed over the wire, within defined bounaries, so two identical requests
>against an identical service may legitimately return different sets of
>axioms, without the requester becomming confused or behaving differently.
>Hence, the only thing that uniquely identifies the set of axioms is the set
>of axioms itself.
>So, the things we are moving about:
>a) have no physical location, ever (they are generated by software, streamed,
>consumed by software)


>b) have no logical URI that identifies them, or any other identifier smaller
>than themselves

Don't have in fact, or can't have because you don't want to ever give 
them one? If the latter, why not?

>c) are a sub-set of the axioms entailed by some other ontology, which does
>have a logical URI
>Is there some other top-level element other than Ontology that better fulfills
>these needs?

Whats wrong with Ontology? Nothing you have said is inconsistent with 
these things being in the class Ontology. They don't HAVE to have a 
URI, you could refer to them with Bnodes. But in fact it is a very 
low-cost business to construct a unique URI, rather like gensym in 
GOFLISP. Use, say, the base URI of the derived-from ontology and 
append the real time in seconds the thing was streamed. Or whatever. 
Of course if you try to GET or owl:import that URI things will break. 
So, don't.

>If not, is there some standard way to indicate to tools that the ontology has
>no physical or logical URI, but is a) a sub-set of the axioms in another
>ontology or b) the axioms entailed by another ontology or c) a sub-set of the
>axioms entailed by another ontology?

Not a standard, but you could invent this subclass of Ontology if you 
want, call them EvanescentOntologies or something.



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Received on Wednesday, 31 October 2007 22:03:14 UTC

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