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Re: LC comments 18, 19, 59

From: Ivan Herman <ivan@w3.org>
Date: Fri, 20 Mar 2009 09:16:52 +0100
Message-ID: <49C350F4.6000200@w3.org>
To: Ian Horrocks <ian.horrocks@comlab.ox.ac.uk>
CC: public-owl-wg@w3.org

I have no problem with the LC comment answer itself (being one of the
addressees:-), ie, I am happy to see that shipped.

However, I am looking for ways to improve the Profile draft
editorially... I indeed wonder whether we should not slightly rewrite or
at least add something to the intro part of QL. Whereas the intro to RL
spells out one of the main features of RL which makes it important for
potential users ("This is achieved by defining a syntactic subset of OWL
2 which is amenable to implementation using rule-based technologies"),
the intro part of QL contains exclusively reasoning-complexity type
arguments that is barely clear for potential users. The text in the
document overview says:

OWL 2 QL enables conjunctive queries to be answered using standard
relational database technology; it is particularly suitable for
applications where relatively lightweight ontologies are used to
organize large numbers of individuals or where it is useful or necessary
to access the data directly via relational queries (e.g., SQL).

and I wonder whether that text should not be added to the QL
introduction as the first paragraph. The second (currently first)
paragraph is really for experts/implementers only.

If this is done, than the text have just added half-phrase to make it
clear _why_ this feature is not there.

Note that OWL 2 QL does not support SameIndividual assertions, because
then queries could not be answered by standard SQL queries any more. In
order to handle ontologies that include SameIndividual assertions but
are otherwise OWL 2 QL, one could use either a preprocessing step that
materialises the SameIndividual relation or an extension of the
rewriting technique that rewrites into recursive queries.




I added a statement about sameIndividual. Here is the diff:


No doubt it can be improved, but I suggest that we keep it rather brief.

If we are happy with this (or with a suitably improved version) then
we can send the responses.



Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
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Received on Friday, 20 March 2009 08:16:41 UTC

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