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Re: owl:imports vs xinclude

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Sun, 25 Nov 2007 05:32:58 -0500 (EST)
Message-Id: <20071125.053258.235687617.pfps@research.bell-labs.com>
To: jjc@hpl.hp.com
Cc: public-owl-wg@w3.org

[See below for my take on how importing works in the various OWLs.] 

From: Jeremy Carroll <jjc@hpl.hp.com>
Subject: owl:imports vs xinclude
Date: Thu, 22 Nov 2007 14:29:10 +0000

[...]

> Please can someone give a partisan and biased account of:
> 
> a) what's wrong with owl:imports

Nothing.  :-)

> and
> 
> b) why xinclude fixes it

XML inclusions provide similar power to the import-by-location view of
imports that is in OWL Full, so use it instead of duplicating it.  

> (My gut feel is that this seems like unnecessary change, but since I 
> don't understand the motivations, I thought I should ask before a 
> knee-jerk disagreement!)

[...]

> Thanks
> 
> Jeremy



Importing ontologies in OWL DL [OWL S&AS 3.4]:

  [A]n owl:imports annotation also imports the contents of another OWL
  ontology into the current ontology. The imported ontology is the one,
  if any, that has as name the argument of the imports construct. (This
  treatment of imports is divorced from Web issues. The intended use of
  names for OWL ontologies is to make the name be the location of the
  ontology on the Web, but this is outside of this formal treatment.)

Importing ontologies in OWL Full [OWL S&S 5.3]:

  Definition: Let K be a collection of RDF graphs. K is imports closed
  iff for every triple in any element of K of the form x owl:imports u
  . then K contains a graph that is the result of the RDF processing of
  the RDF/XML document, if any, accessible at u into an RDF graph. The
  imports closure of a collection of RDF graphs is the smallest
  import-closed collection of RDF graphs containing the graphs.

Importing ontologies in OWL DL in the Web [OWL S&S 5.4]:

  Definition: Let T be the mapping from the abstract syntax to RDF
  graphs from Section 4.1. Let O be a collection of OWL DL ontologies
  and axioms and facts in abstract syntax form. O is said to be imports
  closed iff 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.


My summary of the OWL 1.0 situation:

The situation for OWL DL is quite clear - the ontology retrievable at
URI u is supposed to have name u.  It is thus irrelevant whether imports
is by location or by ontology name.  For OWL Full, it is not required
that the ontology at u have name u, but it is clear that imports is by
location.  

The end result is that in OWL 1.0, imports works like entire-document
XML inclusion.


Importing ontologies in OWL 1.1 [SS&FS 3]:

  Each ontology contains a possibly empty set of import declarations. An
  ontology O directly imports an ontology O' if O contains an import
  declaration whose value is the ontology URI of O'. The relation
  imports is defined as a transitive closure of the relation directly
  imports. The axiom closure of an ontology O is the smallest set
  containing all the axioms of O and of all ontologies that O
  imports. Intuitively, an import declaration specification states that,
  when reasoning with an ontology O, one should consider not only the
  axioms of O, but the entire axiom closure of O.

My summary of the OWL 1.1 situation:

There is no treatment of importing in the OWL 1.1 Semantic document,
which is a bit strange, so the controlling definition of importing in
OWL 1.1 is in the SS&FS document.  The definition is a bit unfinished,
but the intent is clear that imports is by name, as in the OWL DL direct
semantics, but without the intent that names and locations correspond.


My take on imports vs XML inclusions is that XML includes is compatible
with an imports-by-location mechanism, but that XML inclusions provide
much more power.  I do not believe that XML inclusions are appropriate
for any non-XML OWL syntax, as they are too tied to XML.  I do not
completely know whether (full) XML inclusions would be appropriate for
an XML-based OWL syntax, but it appears that they might be, provided
that imports-by-location is the imports paradigm that is wanted.

Peter F. Patel-Schneider
Bell Labs Research
Received on Sunday, 25 November 2007 10:50:43 GMT

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