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imports in S&AS

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Tue, 25 Mar 2003 13:43:42 +0100
To: <www-webont-wg@w3.org>
Message-ID: <BHEGLCKMOHGLGNOKPGHDAEFECBAA.jjc@hpl.hp.com>


I am reviewing some of my earlier issues with S&AS.
The good news is that nearly all of them are now fixed.

On imports, I have one minor but critical issue for Peter, and some
discussion primarily intended for others in the WG (Peter and I had a brief
discussion at the editors meeting - and I am not *too* unhappy with the
current state).

Critical issue:
===============

The link
http://www-db.research.bell-labs.com/user/pfps/owl/semantics/rdfs.html#RDF_g
raph_imports_closure
does not lead to a definition of imports closure.

I use this link in
http://www.w3.org/2002/03owlt/editors-draft/snapshot#syntaxConformance

Suggest add new definition:
[[
Definition: The imports closure of an RDF graph K is the union of the
smallest imports closed set of RDF graphs containing K.
]]
(it seems odd to me to keep talking about sets of graphs rather than just
one)

I could put this definition into test cases, but this would seem odd to me.

More General Discussion
=======================
In S&AS the underlying model of imports is driven from the abstract syntax.
In particular the model suggests that the documents imported are themselves
abstract syntax documents - this is in tension with the WG decision about
imports which is essentially triple based.
In other words, S&AS (OWL DL) assumes that imported ontologies are in OWL
DL, whereas the WG decision is that an OWL DL ontology can import documents
that are *not* well-formed OWL DL, but taken together form an OWL DL graph.
I am not too unhappy because, while I think the text is confusing on this
point, I see no operational impact.


Critical phrases:
section 2.1
"idealizations of this operational meaning for imports are used"
2.3
"If an ontology imports another ontology, the axioms in the imported
ontology (and any ontologies it imports, and so on) can be used for these
purposes"
(assuming that the imported document *has* axioms)

3.4
in definition of satisifies
"I satisfies each ontology mentioned in an owl:imports annotation directive
of O."
(again assuming that the imported ontology is in OWL DL)

4 mapping rules
no mention of imports
This is the key disconnect between imports in the abstract syntax, and
imports in the concrete syntax - which is why Peter and I are not arguing
this point!

5.4 OWL DL

"Definition: Let T be the mapping from OWL ontologies in the abstract syntax
to RDF graphs from Section 4.1. Let O be a collection of OWL DL ontologies
in abstract syntax form. If for any URI, u, in an imports directive in any
ontology in O the RDF parsing of the document accessible on the Web at u
results in T(K), where K is the ontology in O with name u. Then O is said to
be consistent with the Web. "

Again this disconnects with the definition of an OWL DL document which is
one whose import closure is an RDF graph that corresponds to a collection of
OWL DL ontologies.

Test Case:
=========

http://www.w3.org/TR/owl-test/#imports-008

OWL Full <imports/imports008>:

first:sub rdf:type rdfs:Class .
first:sub rdfs:subClassOf first:super .

and

OWL Lite <imports/main008>:

<imports/main008> rdf:type owl:Ontology .
<imports/main008> owl:imports <imports/imports008> .
first:sub rdf:type owl:Class .
first:super rdf:type owl:Class .


The definition of "consistent with the Web" is not applicable to this test
case - this does not bother me too much since I do not see the concept as
necessary for OWL, but it does strike me as somewhat broken. My preferred
treatment would be to have imports as an operation on RDF graphs and leave
the abstract ontologies out of it all together.

Jeremy
Received on Tuesday, 25 March 2003 07:43:30 GMT

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