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RE: LANG: need to CLOSE Issue 5.6 Imports as magic syntax

From: Smith, Michael K <michael.smith@eds.com>
Date: Tue, 29 Oct 2002 16:07:55 -0600
Message-ID: <B8E84F4D9F65D411803500508BE32214118004F1@USPLM207>
To: Jeff Heflin <heflin@cse.lehigh.edu>, Jim Hendler <hendler@cs.umd.edu>
Cc: webont <www-webont-wg@w3.org>

2 more cents.

> 3) The imports triples are considered extra-logical, and any statements
> that contain owl:imports as a subject or object are undefined.
> Furthermore, any imports statements that have a resource other than the
> containing document as a subject are undefined.

OK.  

> 2) The semantics essentially be "A imports B means if B entails P then A
> entails P." ...

Imports is extra-logical by 3.  It has no formal semantics.  

I know what you are trying to get at, I just don't think we have
figured out how to say it.  And I don't know how to say it except
operationally.  We all agree (?) that if importing B works (because
all of my internet connections are working, the document B exists, 
the server it resides on is up, my firewall and anti-virus
software are happy, ..., and A gets augmented with B) then the 
resulting KB will entail P.

I would be inclined to a statement like:

 The owl:imports statement is extra-logical.  It has an operational
 interpretation.  The containing ontology is extended by the content
 of the imported ontologies.  This extension is performed recursively
 until there are no more imports to apply.  This attempt to extend
 the ontology may not always be completely successful.  The effect of
 such failure is implementation defined.

 If the interpretation of 'A owl:import B' is successful, then the
 entailments derivable from the resulting KB are those derivable from
 the union of the contents of A and B.

- Mike

-----Original Message-----
From: Jeff Heflin [mailto:heflin@cse.lehigh.edu]
Sent: Tuesday, October 29, 2002 9:21 AM
To: Jim Hendler
Cc: webont
Subject: Re: LANG: need to CLOSE Issue 5.6 Imports as magic syntax



Jim,

I believe you are correct that there is consensus on the points you
detail below. It seems to me that there are three issues currently
unresolved.

1) Should an imports failure make the imports statement "true by
default" as suggested by Pat in [1]. I argued problems with this in [2]
and suggested that the "A imports B means if B entails P then A entails
P" solution is better. I have not heard a counter-argument on this
point. Perhaps silence can be taken as assent?

2) Should we have an operational semantics as opposed to a
entailment-based smenatics as argued by Massimo [3]. The operational
solution is more constraining: it requires developers to implement
things in a certain way. The entailment semantics on the other hand
allows Massimo to implement his operational solution, but allows other
developers to implement things differently. This is a key feature of the
entailment-based solution.

3) How should error conditions be handled (e.g., 404 errors). Some
people have argued that the system should report errors to users, others
that additional triples should be added to the graph. I do not think we
will reach consensus on this. However, the entailment-based solution
once again embraces the various opinions. It simply says if you don't
draw all the inferences then your reasoning is incomplete (see [4]).
Thus, particular implementors are free to provide warning messages,
error messages, meta-information in the graph, or whatever else they
choose when such situations arise.

Therefore, I propose the following:

1) The syntax for imports be the same as that of DAML+OIL

2) The semantics essentially be "A imports B means if B entails P then A
entails P." Here A and B can be any document, not just ontologies. Also
note that when a document does not contain an imports statement, we do
not specify a mechanism for determining what statements from other
documents are entailed. Thus, developers are free to implement various
things, just as they are free to combine arbitrary unlinked documents.
However, in such situations, they take responsibility for the
conclusions they make.

3) The imports triples are considered extra-logical, and any statements
that contain owl:imports as a subject or object are undefined.
Furthermore, any imports statements that have a resource other than the
containing document as a subject are undefined.

I suggest that anybody who cannot live with this solution speak up now
and clearly explain how this would break their applications. If there
are no serious objections with it, I'd be happy to write up the details
of this proposal.

Jeff

[1] http://lists.w3.org/Archives/Public/www-webont-wg/2002Oct/0057.html 
[2] http://lists.w3.org/Archives/Public/www-webont-wg/2002Oct/0141.html
[3] http://lists.w3.org/Archives/Public/www-webont-wg/2002Oct/0060.html
[4] http://lists.w3.org/Archives/Public/www-webont-wg/2002Oct/0150.html

Jim Hendler wrote:
> 
> I believe we have reached strong consensus on the outline of a
> solution, but are still grappling with details.  Someone needs to
> take the action to resolve this.  Here is my understanding of an
> outline as to what we have consensus on:
> 
> i. When a document contains an explicit imports statement, the intent
> is that the triples in the imported document are treated basically as
> if they were in this document.  Thus, if one document states that
> Socrates is a man, and it imports a document which states that Men
> are mortal, then the consensus is that one should believe that
> Socrates is mortal.
> 
> ii. When a document does not contain an explicit imports statement,
> but does reference a second document, then we had consensus that it
> need not be determined (by us) whether all, some, or none of the
> triples from the second document should be treated as if they were in
> this document - the policy is left to the implementor (we might
> suggest a possible policy in one of our documents).  Thus, if one
> document states that Socrates is a man, and it refers to a document
> which states that Men are mortal, then the consensus is that it is a
> matter of policy left to implementors to  decide whether to believe
> that Socrates is mortal
> 
> iii. There is consensus that imports statements can include
> references to any document, not just ontologies (allowing the import
> of instances)
> 
> iv. There is consensus that imports statements are "extra logical" in
> the sense that it should be undefined as to the meaning of
> subclassing or etc. of imports. (i.e. details left undetermined by us)
> 
> Given the above, we need a means for describing this.  Jeff and Pat
> have produced emails about the issue of entailment across documents,
> but that seems to have gone unresolved.
> 
> We need to close this issue somehow - suggestions?
>   -JH
> 
> --
> 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)
> http://www.cs.umd.edu/users/hendler
Received on Tuesday, 29 October 2002 17:08:30 GMT

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