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Re: draft response for LC comment 50

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Tue, 17 Feb 2009 07:08:10 -0500 (EST)
Message-Id: <20090217.070810.216044991.pfps@research.bell-labs.com>
To: ian.horrocks@comlab.ox.ac.uk
Cc: public-owl-wg@w3.org
I used "standardized" as that is the wording in the RDF semantics
document, where the procedure is defined.  I think that the opaqueness
of the term is of benefit, as the allusion to naming appears to be part
of what was causing the problem.


From: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>
Subject: Re: draft response for LC comment 50
Date: Tue, 17 Feb 2009 10:13:05 +0000

> Looks good -- thanks.
> Minor comment: you change "named apart" to "standardised apart". This
> may be better, but is still relatively opaque. I wonder if anyone can
> think of anything better? I'm not to worried about this though because
> there is a clear explanation of what it means that is pointed to
> whenever it is used.
> Ian
> On 14 Feb 2009, at 04:32, Peter F. Patel-Schneider wrote:
>> [Response for LC Comment 50:]
>> Dear Jonathan,
>> Thank you for your message
>>   http://lists.w3.org/Archives/Public/public-owl-comments/2009Jan/0052.html

>> on the OWL 2 Web Ontology Language last call drafts.
>> It is quite often common to be a bit sloppy about the distinction
>> between names and whatever they denote or mean, consider, for example,
>> the common use of "the variable x" instead of "the variable named x".
>> Often the loss in precision is gained back in readability.  In the
>> interests of gaining this readability, the OWL Functional Syntax
>> generally does not use markers in its syntactic categories to indicate,
>> for example, "ClassName" or "ClassID", instead using just "Class".
>> Of necessity, this breaks down for individuals.  The overall syntactic
>> category in the OWL Functional Syntax is "Individual", which is then
>> divided into "NamedIndividual" and "AnonymousIndividual".  The
>> alternative "IndividualName" and "IndividualAnonymousMarker" would have
>> been a reasonable alternative, but would have somewhat conflicted with
>> the usage for other syntactic categories.
>> As you point out, there are some parts of the document that should be
>> revised so as to not be so confusing.
>> The WG has decided to make the following modifications in response to
>> your comments:
>> Section 3.4:
>> 	The axiom closure of an ontology O is the smallest set that
>> 	contains all the axioms from each ontology O' in the import
>> 	closure of O with all anonymous individuals *standardized* apart
>> 	— that
>> 	is, the anonymous individuals from different ontologies in the
>> 	import closure of O are treated as being different; see Section
>> 	5.6.2 for further details.
>> Section 5.6:
>> 	Individuals in the OWL 2 syntax represent actual objects
>> 	*(semantic individuals)* from the domain being modeled. There
>> 	are two types of individuals in *the syntax of* OWL 2. Named
>> 	individuals are given an explicit name that can be used in any
>> 	ontology ** to refer to the same *semantic*
>> 	individual. Anonymous individuals *do not have this global name
>> 	and thus* are local to the ontology they are contained in.
>> Section 5.6.2:
>> 	Special treatment is required in case anonymous individuals with
>> 	the same node ID occur in two different ontologies. In
>> 	particular, these two individuals are structurally equivalent
>> 	(because they have the same node ID); however, they are *not*
>> 	treated
>> 	as *identical* in the semantics of OWL 2 (because
>> 	anonymous individuals are local to an ontology they are used
>> 	in). The latter is achieved by *standardizing* anonymous
>> 	individuals
>> 	apart when constructing the axiom closure of an ontology O: if
>> 	anonymous individuals with the same node ID occur in two
>> 	different ontologies in the import closure of O, then one of
>> 	these individuals MUST be replaced in the axiom closure of O
>> 	with a fresh anonymous individual (i.e., with an anonymous
>> 	individual having a globally unique node ID).
>> Section 5.6.2 Example 2:
>> 	In order to ensure that these individuals are treated
>> 	differently by the semantics they are *standardized* apart when
>> 	computing the axiom closure of O1 — either _:a5 in O1 is
>> 	replaced with a fresh anonymous individual, or this is done for
>> 	_:a5 in O2.
>> Section 9.5:
>> 	OWL 2 supports a rich set of axioms for stating assertions —
>> 	axioms about individuals that are often also called facts. For
>> 	clarity, different types of assertions are shown in three
>> 	separate figures, Figure 18, 19, and 20. The SameIndividual
>> 	assertion allows one to state that several individuals are all
>> 	equal to each other *(more precisely, the several different
>> 	individuals in the syntax denote the same semantic individual)*,
>> 	while the DifferentIndividuals assertion allows for the opposite
>> 	— that is, to state that several individuals are all different
>> 	from each other *(more precisely, that the several different
>> 	individuals in the syntax are also semantically different)*. The
>> 	ClassAssertion axiom allows one to state that an individual is
>> 	an instance of a particular class.
>> Section 11:
>> 	The axiom closure Ax (with anonymous individuals *standardized*
>> 	apart
>> 	as explained in Section 5.6.2) of each OWL 2 ontology O MUST
>> 	satisfy the global restrictions defined in this section. As
>> 	explained in the literature [SROIQ], this restriction is
>> 	necessary in order to obtain a decidable language. The formal
>> 	definition of these conditions is rather technical, so it is
>> 	split into two parts. Section 11.1 first introduces the notions
>> 	of a property hierarchy and of simple object property
>> 	expressions. These notions are then used in Section 11.2 to
>> 	define the actual conditions on Ax.
>> The diffs can be found at ..................................
>> The Direct Semantics document includes renaming of anonymous
>> individuals, and has been appropriately edited.
>> The diffs can be found at .......................
>> The WG considers these to be editorial changes.
>> Please acknowledge receipt of this email to
>> <mailto:public-owl-comments@w3.org> (replying to this email should
>> suffice). In your acknowledgment please let us know whether or not you
>> are satisfied with the working group's response to your comment.
>> Regards,
>> Peter F. Patel-Schneider
>> on behalf of the W3C OWL Working Group
Received on Tuesday, 17 February 2009 12:08:25 UTC

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