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Re: [Fwd: Re: RDFCore Comments on OWL Reference]

From: pat hayes <phayes@ihmc.us>
Date: Mon, 16 Jun 2003 17:13:02 -0500
Message-Id: <p05210603bb13eddeb52b@[]>
To: Brian McBride <bwm@hplb.hpl.hp.com>
Cc: w3c-rdfcore-wg@w3.org

>We suggest to add the following sentence to the first paragraph of Sec. 3.1:
>A class description describes am OWL class, either by a class name or
>by specifying a class extension of an unnamed anonymous class.
>   >
>   > Whilst this is just wordsmithing, the concept of a class description
>   > is of prime importance to the rest of the spec and should be clear.
>   >
>   > Further:
>   >
>   > [[
>   > NOTE: If one provides an RDF identifier for class descriptions of
>   > he type 2-6, this has the extra effect of providing a way of
>   > referring to the class description by its name, i.e., as a class
>   > description of type 1. See Section 3.2.3 for details.
>   > ]]
>   >
>   > Does this name identify the class description, or the class
>   > described by the description?  We suspect the latter, in which case:
>   >
>   > [[
>   > NOTE: If one provides an RDF identifier for class descriptions of
>   > the type 2-6, this has the extra effect of providing a way of
>   > referring to the class so described by its name. See Section 3.2.3 for
>   > details.
>   > ]]
>Well, this was confusing. The note should read:
>NOTE: If one provides an RDF identifier for class descriptions of
>he type 2-6, this is not considered to be a class description, but a
>special kind of class axiom for complete classes.
>See Section 3.2.3 for details.
>   > There are other instances of this confusion: e.g. in 3.1.2
>   >
>   > [[
>   > A value constraint puts constraints on the value range of the
>   > property when applied to this particular class description.
>   > ]]
>   >
>   > The constraint is on the property when applied to an instance of the
>   > class described by this particular class description.
>   >
>   > In 3.2
>   >
>   > [[
>   > * rdfs:subClassOf allows one to say that the class extension of a
>   > class description is a subset of the class extension of another class
>   > description.
>   > ]]
>We agree that in some place where it reads "the class description" it
>should be read as "the class described by the class
>description". As such a global change would make the text less
>accessible and as there typically is no ambiguity, we propose to add
>to Sec. 3.1. the following note:
>NOTE: In this document we sometimes use for readability purposes
>the shorthand "class description" to refer to "the class being
>described by the class description". Strictly speaking, these are
>different in the case of class descriptions of type 2-6: the class is
>represented by the corresponding blank node; the class description is
>represented by the triple that have this blank node as their subject.

I do not think this is acceptable.  The literature is particularly 
prone to use/mention category errors of this kind, and they have in 
the past been particularly troublesome to foundational discussions in 
the SW development effort. One can point to the long-standing 
confusions surrounding the RDF reification vocabulary as one example. 
For such confusions to be repeated in the text of a specification as 
complex and semantically sensitive as OWL is therefore particularly 
troubling, and we feel that the text should be rewritten carefully so 
as to avoid these confusions and make it intended meaning completely 
clear. We are not convinced that there is "no ambiguity" in these 
cases, and we do not feel that writing the text so as to be clear and 
unambiguous about use/mention distinctions is likely to make the text 
"less accessible".

The suggested explanatory text is itself ambiguous: it is not clear 
what is meant by saying that  "the triple (sic: should be 'triples?) 
that have the blank node as their subject"  *represent* the class 
description.  According to the RDF semantics, what a set of triples 
represents ought to be a truth-value in an interpretation, or 
possibly something that could be called a proposition or an 
assertion. None of these seem to be what is meant by the phrase 
"class description". Is the intent of this sentence to indicate that 
the triples with the common subject *are* the class description?

It might be clearer if the word 'represent' and its cognates were 
replaced by the more precise terminology based on 'denote'. This 
would at least have the side-effect of removing ambiguity.


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Received on Monday, 16 June 2003 18:13:06 UTC

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