- From: Brian McBride <bwm@hplb.hpl.hp.com>
- Date: Mon, 06 Jan 2003 17:21:19 +0000
- To: public-webont-comments@w3.org
I've been reading through the editor's version of the owl guide at:
http://www.daml.org/2002/06/webont/owl-ref-proposed
version
$Id: owl-ref-proposed.html,v 1.112 2003/01/03 04:35:38 mdean Exp $
The editors may find the following comments useful. These comments are
from me alone in my capacity as an interested individual. I have marked
those I feel deserve a response, though they are largely editorial in
nature, with SUBSTANTIVE or TECHNICAL.
I realise that I am not referring to a published WD and am commenting on
work in progress. However, I hope the editors may find these useful in the
final stages of polishing this document.
Some of these comments are duplicates of ones I have made before
http://lists.w3.org/Archives/Public/public-webont-comments/2002Dec/0004.html
but are not listed in the editor's list of comments being addressed, so
perhaps bear repeating, lest they were missed.
http://lists.w3.org/Archives/Public/www-webont-wg/2003Jan/0071.html
1.
The abstract refers to the RDF/XML syntax doc. The concepts doc may be
more appropriate.
2.
[[ * OWL Lite is detailed in the Feature Synopsis for OWL Lite and OWL
[OWL Features].]]
"Detail" is not a verb. What does this sentence mean?
3. SUBSTANTIVE
[[An OWL knowledge base is a collection of RDF triples as defined in the
RDF/XML Syntax Specification (Revised) [RDF/XML Syntax].]]
Again I would have expected the concepts doc to be the appropriate
reference here.
4.
[[This document specifies which collections of RDF triples constitute the
OWL vocabulary and what the prescribed meaning of such triples is.]]
The owl vocabulary is a collection of triples? That seems like a type
mismatch. I'd expect a vocabulary to be a collection of names, in this
case RDF URIREF's.
5. SUBSTANTIVE
[[OWL only provides a semantic interpretation for those parts of an RDF
graph that instantiate the schema defined in http://www.w3.org/2002/07/owl.]]
What does it mean for "part of an RDF graph" to "instantiate" a schema? Is
the term "instantiate" defined anywhere? RDFS has no such notion.
I'm finding it a bit bizarre that RDF Schema is being used to define the
syntax of a language.
6. SUBSTANTIVE
owl:backwardCompatibleWith
What does this actually mean?
Given:
o1 owl:backwardCompatibleWith o2 .
does that entail
o1#foo owl:sameAs o2#foo .
for all foo defined in o2. Does that include foo's that are in the o2
'namespace' but are not actually defined in the ontology which can be
retrieved from o2? What is a sufficient condition to allow stating that
one ontology is backward compatible with another. How are imports affected
by owl:backwardCompatibleWith? If an ontology drops an import can it still
be backward compatible with its previous version. If it changes an import
to one that is backward compatible, is it still backward compatible?
I think the meaning of this needs spelling out more clearly.
7. SUBSTANTIVE
[[OWL divides the universe into two disjoint parts. One part consists of
the values that belong to XML Schema datatypes. This part is called the
datatype domain.]]
RDF allows for datatypes that are not XML Schema datatypes, but conform to
the XML Schema datatype model. The text here rules out such datatypes. Is
that intended?
Later the doc states:
[[OWL also allows the use of XML Schema datatypes to describe (or define)
part of the datatype domain.]]
I think this is contradicting the previous statement, but the language
isn't very clear to me. Is this a syntactic statement - that xml schema
datatype declarations are allowed as part of an owl ontology?
8. SUBSTANTIVE
[[RDFS and OWL allow cycles of subclass relationships as a means to assert
equality between classes.]]
Can we be clearer about what is meant by equality here? I think you mean
that a cycle of subclass relationships states that the classes in the cycle
have the same membership, but not that they are identical.
9. SUBSTANTIVE
[[ Each owl:sameClassAs element asserts that C is equivalent to the
class-expression in the element (ie. C and all the class-expression must
have the same instances);]]
Is there a first class notion of class equivalence here? If so it may
deserve more weight than a parenthetical comment.
Given the semantics, the name 'sameClassAs' is misleading.
10. TECHNICAL
I note that owl:sameClassAs is not defined as a subproperty of
owl:sameAs. Should it be?
I'm coming back to this comment after reading further on. It maybe that it
should not be, but its not really clear to me. I'm wondering what exactly
the semantics of owl:sameAs are. In owl full, given X to be a class, a
property and an individual would:
X owl:sameAs Y .
entail
X owl:sameClassAs Y .
X owl:samePropertyAs Y .
X owl:sameIndividualAs Y .
If that is the semantics then owl:sameClassAs should not be a subproperty
of owl:sameAs, since that would prohibit one saying that two classes have
the same members, but are not the same individuals.
But, thinking about it, that can't be the semantics can it, because if it
were, then one would not be able to use owl:sameAs in place of
owl:sameClassAs as suggested in the doc, as they don't mean the same thing
in full owl. I'm confused.
It would be useful to have the definition of the meaning of owl:sameAs all
in one place.
11.
[[# The class C must be equivalent to the class defined by each of the
boolean class expression,
and ..]]
I assume that the equivalent here is the one defined in parenthesis
above. An internal link would be useful where such first class notions are
used.
12. SUBSTANTIVE
[[ * a boolean combination of class expressions, enclosed in
<rdfs:Class>...</rdfs:Class> tags
]]
Was <owl:Class>...</owl:Class> meant here? If not, some comment on why not
might be appropriate.
13. SUBSTANTIVE
[[Each class expression either refers to a named class, namely the class
that is identified by the URI, or implicitly defines an anonymous class,
respectively the class that contains exactly the enumerated elements, ...]]
Should that be "...respectively a class that contains exactly...". The
current text suggests that there is only one such class. A similar comment
applies to each of the following clauses.
14. SUBSTANTIVE
[[Two class names are already predefined, namely the classes owl:Thing and
owl:Nothing. Every object is a member of owl:Thing, and no object is a
member of owl:Nothing. Consequently, every class is a subclass of owl:Thing
and owl:Nothing is a subclass of every class.]]
I take these are the definitions of owl:Thing and owl:Nothing. The
defining text
[[Every object is a member of owl:Thing]]
does not rule out things other than objects being members of owl:Thing and
it should. Similarly for owl:Nothing.
15. SUBSTANTIVE
[[A property restriction is a special kind of class expression. It
implicitly defines an anonymous class, namely the class of all objects that
satisfy the restriction. ]]
Similar to above, is it "the class of all objects..." or "a class ..."
16. SUBSTANTIVE
[[An owl:Restriction element contains an owl:onProperty element, which
refers to a property name (a URI) ...]
should that be "(an RDF URI Reference)" with a link to the appropriate
definition or are OWL property names restricted to being URI's?
17. SUBSTANTIVE
[[ An owl:allValuesFrom element defines the class of all objects for whom
the values of property P...]]
Similar to above, should that be "a class of ..."
18. typo?
[[an owl:someValuesFrom element (which contains a class expression or a
datatype references).]]
Should that be "datatype reference)."?
19. typo?
[[observe that the owl:allValuesFrom restriction demands that all values
of P belong to class P]]
Did you mean class *P*.
20. SUBSTANTIVE
[[an owl:intersectionOf element, containing a list of class expressions.
This defines the class that consists of exactly all the objects that are
common to all class expressions from the list. ]]
As above should it be "a class"? Similarly for owl:unionOf and
owl:complimentOf.
21. SUBSTANTIVE
[[An rdf:Property element refers to a property name (a URI) (to which we
will refer as P)]]
Should that be an RDF URI Reference rather than a URI? Is it the URI(REF)
that is referred to as P or the property element. None of these I think,
as the doc later discusses subproperties of P, which makes P a property.
There is a similar issue with the earlier wording:
[[A class element, owl:Class, contains (part of) the definition of an
object class. A class element refers to a class name (a URI) (we will refer
to this class as C) and contains...]]
What class?
22.
It seems a bit strange to be defining the semantics of rdfs:subPropertyOf,
rdfs:domain and rdfs:range here with no reference to the RDF schema
definitions.
23.
[[zero or more owl:samePropertyAs elements (each containing a property name).
Each owl:samePropertyAs element asserts that P is equivalent to the named
property (i.e. they must have the same instances),]]
If this is a first class notion of property equivalence, then it deserves
greater status than a parenthetical comment.
I also suggest that it, like owl:sameClassAs, is misnamed since I assume
(it not being clear from this document so far) that properties are defined
intensionally. owl:equivalentTo perhaps.
24. TECHNICAL
Should owl:samePropertyAs be defined as a subproperty of owl:sameAs?
Similar comment to 10.
25. SUBSTANTIVE
We have part of the definition of owl:sameAs here. But if we follow the
link to to the definition of owl:sameAs
http://www.daml.org/2002/06/webont/owl-ref-proposed#sameAs-def
we find ourselves in the section on Class elements, which clearly does not
contain a complete definition of owl:sameAs. That doesn't seem like a good
thing. I wonder if there is any more to owl:sameAs we haven't heard of
yet, e.g. can it be applied to an individual? Checking
http://www.daml.org/2002/06/webont/owl
it has no range constraint so presumably it can be. But where is its
meaning defined? But we also notice ...
26. SUBSTANTIVE
in
http://www.daml.org/2002/06/webont/owl
we find:
[[<Property rdf:ID="sameAs"> <!-- equals? equiv? renames? -->
<rdfs:label>sameAs</rdfs:label>
<comment>
for sameAs(X, Y), read X is an equivalent term to Y.
</comment>
</Property>]]
I'm confused by the comment. I'm not sure what a 'term' is here. Is it
needed? Does not "read X is equivalent to Y" do just as well. Or is there
some meaning to "term".
27. SUBSTANTIVE
[[ Each owl:inverseOf element asserts that P is the inverse relation of the
named property.]]
Similar to the "the class" comments above, should that be "that P is an
inverse of the named property"?
28.
[[To state that objects are the same, an owl:sameIndividualAs element is
used. (Note that owl:sameAs can be also used here, but owl:sameIndividualAs
is preferred.)]]
More of the definition of owl:sameAs. Should be collected into one place.
29. SUBSTANTIVE
[[See issue #I5.18-Unique-Names-Assumption-Support-in-OWL. The situation is
different for datatype values, where XML Schema Datatype identity is used. ]]
You need to be clear exactly what identity is meant here. There are issues
with schema datatypes where the same value from the value space of
different datatypes is not considered by xml schema datatypes to be equal.
30. SUBSTANTIVE possibly TECHNICAL
[[By deprecating a term, it means that the term should not be used in new
documents that commit to the ontology.]]
I'm not sure what is meant by term here. Does it mean the name, or the
thing denoted by the name. Given:
C rdf:type owl:deprecatedClass .
does that mean that the name 'C' is deprecated or the class C. Test case,
does:
C rdf:type owl:deprecatedClass .
D owl:sameIndividualAs C .
entail
D rdf:type owl:deprecatedClass .
I'm assuming the answer must be yes, but in which case the reference to
"term" isn't appropriate.
Done for now. I hope that this is helpful.
Brian
Received on Monday, 6 January 2003 12:20:02 UTC