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ACTION-320 Review profiles

From: Jie Bao <baojie@cs.rpi.edu>
Date: Wed, 1 Apr 2009 12:06:58 -0400
Message-ID: <b6b357670904010906u60fb6a7esd339cc257f1c0f62@mail.gmail.com>
To: W3C OWL Working Group <public-owl-wg@w3.org>
Review of OWL 2 Profile

By Jie Bao

The version I looked at was:

http://www.w3.org/2007/OWL/wiki/index.php?title=Profiles&oldid=19851
(13:45, 17 March 2009)

Profile is in general a well-written, clear technical document. Thank
all editors for a brilliant job.

Some of the detailed comments are given below. In general, my main
high-level comments are that the document should be improved for users
who do not necessarily have logic or computational complexity
background. The distinction between profiles should be further stated
– the current wording does make it quite explicit.

==Introduction==

#0: We should say something about the audience, such as prerequisite
knowledge on RDF for RL (and whatever else). We also need to indicate
that the three profiles are independent from each other, thus a user
only need to read the profiles s/he is interested in. One sentence
should be mentioned that complexity notions are further explained in
section 5.

#1: EL is for “ontologies that contain very large numbers of
properties and/or classes”. This description may not be very clear to
a developer. Emphasis should also be on its relatively simple
structure. It shall also provide information to distinguish from RDFS,
which can also model “very large numbers of properties and/or
classes”.

#2: EL: the notion of “very large numbers” varies from community to
community. To many, thousands of classes are “large”, while to some
others it’s a small set.  I would prefer wording like “ontologies that
mainly model class hierarchies and/or property hierarchies, plus
limited class restrictions such as existential quantifications (i.e.,
predication for the existence of a property value)”

#3: The distinction between EL and RL is still not clear enough.

QL: “applications that use very large volumes of instance data, … The
expressive power of the profile is necessarily quite limited”

RL: “…scalable reasoning without sacrificing too much expressive
power, … trade the full expressivity of the language for efficiency”

To a user, the difference looks quite subtle. Both are about
scalability and limited expressivity.  It also gives the impression
that QL is less expressive than RL. The description to RL is
applicable to other two profiles as well.

#4: In general, the presentation of the targeting applications of the
three profiles should be improved to make their differences more
explicit. Maybe a table with columns “main features, targeting
applications” will help.

==EL==

#5: ontology satisfiability => ontology consistency (to be consistent
with Table 10)

#6:  “captures the expressive power used by many large-scale
ontologies and … can be decided in polynomial time.” – this is
applicable to RL as well.

features that are at risk should be either marked out, or mentioned in
the “Feature At Risk #1” box.

==QL==

#7: the opening paragraph is mainly about complexity and the
underpinning logic of QL. I believe this should be actually the 2nd
paragraph, with the 1st paragraph explaining what QL is for with more
details (e.g., accessing data via a relational query interface).

#8: “this profile contains the intersection of RDFS and OWL 2.” What
features are in RDFS but not in OWL 2? And is it OWL 2 DL or OWL 2
Full?

#9 (3.1): supported features: “assertions other than the equality
assertions” should be “assertions other than individual equality
assertions and negative property assertions”.

not supported features: add “individual equality assertions and
negative property assertions”.

#10 (3.2.5): “OWL 2 QL disallows the use of functional, transitive,
asymmetric, reflexive and irreflexive object properties” contradicts
with the def of ObjectPropertyAxiom  below (which allows
ReflexiveObjectProperty and AsymmetricObjectProperty)

#11 (3.2.5): “OWL 2 QL disallows …  equality axioms”should be “OWL 2
QL disallows …  individual equality axioms”

==RL==

#12 (4): “return all and only the correct answers to certain kinds of
query” –from the wording it’s hard to see what kinds of queries they
are

#13 (4.1) typo “ObjectDataValuesFrom” => “DataSomeValuesFrom”

#14 (4.1) Superclass Expression: (ObjectMaxCardinality 1) should be
“(ObjectMaxCardinality 1/0)”

#15 (4.1) “Thus, OWL 2 RL supports all axioms of OWL 2 apart from…”,
should be OWL 2 Full.

#16 (4.1) the last paragraph: overlaps with the last paragraph of
section 4 and should be merged.

#17 (4.2.1): typo: “OWL 2 RL supports the the predefined classes” – two “the”

#18 (4.2.3): “superClassExpression production defines the classes that
can occur as superclass expressions in SubClassOf axioms” – it can
also appear in range/domain.

#19 (4.2.3) typo: superDataMaxCardinality – shall remove the last “|”

#20 (4.2.5) organization: to be consistent with EL and QL,
ObjectPropertyAxiom  should move up to be after domain/range axioms.

#21 (4.3) “first-order (material) implications” need explanation, esp.
what is “material”.

#22 (Table 4): rule eq-rep-p: owl:sameAs is defined as individual
equality, but p and p’ here are properties

#23 (Table 8): shall we have another rule about DataIntesectionOf?

#24 (Table 9): it looks strange to me that it seems some statements
that can be inferred from the rules are illegal if they are explicitly
added to an ontology. For example, scm-svf2 infers T(?c1,
rdfs:subClassOf, ?c2); however,  SubClassOf (?c1, ?c2) is not a legal
RL statement (since ?c2 is not a superClassExpression)

#25 (Table 9): there are some more that can be inferred about
cardinality restrictions, for example,

If

T(?c1, owl:maxCardinality, "n"^^xsd:nonNegativeInteger)
T(?c1, owl:onProperty, ?p1)
T(?c2, owl:maxCardinality, "n"^^xsd:nonNegativeInteger)
T(?c2, owl:onProperty, ?p2)
T(?p1, rdfs:subPropertyOf, ?p2)

Then

T(?c2 rdf:subClassOf ?c1)

I’m not sure about the complexity consequence of adding those types of
rules. If it still fall within P-TIME, we shall add them.

#26 (after Table 9): for self-containedness, may explain what are
“axiomatic triples of RDF and RDFS”.

#27(Theorem PR1): the motivation of the theorem is not given. I don’t
feel the theorem is needed by developers. It would be better to move
it into the appendix. The proof sketch is also hard to understand, for
example “axioms are of depth at most one” and “derivation tree” are
not defined. I’m also not sure if the DLP rules and the rules in Table
3-8 have one-to-one and complete correspondence.

==Computational Properties==

#28: “PSPACE is the class of problems solvable by a nondeterministic
algorithm” – should be “deterministic algorithm”, even though
NPSPACE=PSPACE.
Received on Wednesday, 1 April 2009 16:07:40 GMT

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