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Proposal to close issue 5.6 - owl:imports

From: Jim Hendler <hendler@cs.umd.edu>
Date: Thu, 14 Nov 2002 08:19:39 -0500
Message-Id: <p0511171ab9f9523f3e60@[]>
To: webont <www-webont-wg@w3.org>
To be able to reach closure on Issue 5.6 we must have a SPECIFIC 
proposal to discuss.  Since we do not have a specific wording on a 
semantics for import, I offer the following compromise position 
instead - please note, this is NOT a proposal to POSTPONE (sorry Dan) 
but rather to CLOSE the issue accepting an imports mechanism, leaving 
the semantic details undetermined at this time.

Proposal to close issue 5.6, owl:imports

1) Change the name to owl:includes
2) Accept the wording from the reference document (copied below from 
[1]) with this name change
3) Accept the wording from the Guide document (copied below from [2]) 
with this name change
4) Place a pointer on the issues list to the WOWG thread entitled "MT 
for imports (was: Re: Imports Proposal)" [3] with a note that the 
Model Theory, because of the time varying nature of the web and the 
difficulty of defining entailment with respect to multiple documents, 
does not specify an exact semantics for owl:includes at this time

Rationale: the current documents explain an inclusion mechanism in 
terms that are clear enough for implementors without being overly 
constraining.  The definitions below are similar to those in 
programming textbooks for includes, and no one seems to have trouble 
implementing and understanding them without a formal model theory.
  i. this would go with our general principle of if we cannot decide 
"do it how D+O does"
  ii. this embraces Ian's philosophy of "if it's research, avoid it" - 
It is clear from the email thread cited in [3]  that an includes 
style mechanism is not research, but formalizing it in MT is
  iii. this proposal is a compromise between those wanting to avoid or 
Postpone having an imports mechanism, and those insisting we must 
formalize it now.

Note: this proposal does provide an imports mechanism, does not 
POSTPONE the issue, but does, in essence, postpone the formal 
semantics of imports which we seem unready to agree to at this time.


from [1]: Reference


Each owl:imports statement references another OWL ontology containing 
definitions that apply to the current OWL resource. Each reference 
consists of a URI specifying from where the ontology is to be 
imported from. See the example above. Imports statements are 
transitive, that is, if ontology A imports B, and B imports C, then A 
imports both B and C. Importing an ontology into itself is considered 
a null action, so if ontology A imports B and B imports A, then they 
are considered to be equivalent.

Note that namespaces only provide a mechanism for creating unique 
names for elements, and do not actually include definitions in the 
way that imports does. Similarly, imports statements do not set up a 
shorthand notation for names. Therefore, it is common to have imports 
statements that correspond to each namespace. However, additional 
imports may be used for ontologies that provide definitions without 
introducing any new names.

from [2]: Guide

<owl:imports> provides an include-style mechanism. <owl:imports> 
takes a single argument, identified by the rdf:resource attribute.

Importing another ontology brings the entire set of definitions 
provided by that ontology into the knowledge base. In order to make 
best use of this imported ontology it would normally be coordinated 
with a namespace declaration. Notice the distinction between these 
two mechanisms. The OWL namespace declaration provides a convenient 
means to reference names defined in other OWL ontologies. 
Conceptually, owl:imports is provided to indicate your intention to 
include the assertions of the target ontology. These assertions 
define the meaning of the terms defined in that ontology, meanings 
that support reasoning about the terms.

Note that owl:imports may not always succeed. As you would expect 
when dealing with the Semantic Web, access to resources distributed 
across the Web may not always be possible. Tools will respond to this 
situation in an implementation defined manner.

[1] http://www.w3.org/TR/owl-ref/
[2] http://www.w3.org/TR/owl-guide/
[3] http://lists.w3.org/Archives/Public/www-webont-wg/2002Nov/0099.html
Professor James Hendler				  hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
Received on Thursday, 14 November 2002 08:19:45 UTC

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