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apologies and regrets

From: Pat Hayes <phayes@ihmc.us>
Date: Mon, 6 Dec 2004 22:52:30 -0600
Message-Id: <p06001f07bdda9b2eedbb@[10.100.0.9]>
To: "Seaborne, Andy" <andy.seaborne@hp.com>, RDF Data Access Working Group <public-rdf-dawg@w3.org>

First, Im sorry Im so far behind, and missed the last telecon. (I 
thought I could attend through IRC, but Mark Greaves pulled the 
network plug during the DAML meeting. ) Second, I have to send 
regrets for tomorrow as well, unfortunately, and will make the next 
week only on a cell phone with no network connection (I should be 
back online by Wednesday of that week).

I agreed to review the definitions in
http://www.w3.org/TR/2004/WD-rdf-sparql-query-20041012/
but its taking a lot longer than I thought it would partly because I 
had a lot of trouble understanding the document. It seems to have a 
lot of internal contradictions (??). Anyway, some of my problems and 
comments and so on are visible in an annotated version at
http://www.ihmc.us/users/phayes/SPARQL-PAT.html
I started trying to edit the text (pink deletions and additions) but 
eventually I had to give up, as I couldnt figure out exactly what it 
meant. Hence the pink verdana-font comments. Sorry if these have a 
rather crotchety tone, they are surface-of-consciousness reactions to 
my frustration at trying to figure out the meaning. Having gone 
through the document twice I think I now have the general picture 
rather clearer; but if Im right, then I think the document needs a 
major re-write, as in its current form it keeps making definitions 
which it then almost immediately contradicts. Eg a pattern is not a 
set, in general.

Anyway, Ive drafted a more positive summary of the way that the 
definitions and constructions might go.
http://www.ihmc.us/users/phayes/SPARQLdefs.html
This is bare definitions, minimal comments, no examples. Stuff in 
italics is comment rather than content.

As per the verdana comments, there seems to be no sense in allowing 
patterns to have bnodes and distinguishing a subset of variables, 
since a pattern variable which is not selected plays exactly the same 
role as a bnode in the pattern would play. Im assuming therefore that 
patterns do not contain bnodes. If this is wrong its easy to tweak 
the definitions, but it only adds complexity and provides no extra 
expressiveness.

General issues that emerged include:

1. Do we want to allow query variables to be placed on parts of 
literals, eg querying the type of a literal or asking for literals of 
a certain type? Or looking for languages:
SELECT ?v WHERE (?x ?p "cat"@?v)
(Why not?)
2. What is an answer to a query with a selected variable which does 
not occur in the pattern?
3. What are the rules for answering a limited-number-of-answers 
query? (do we get the NEXT n answers if we repeat the query?)
4. . Are constraints intended to be normative? The text in 3.1 seems 
to say not, but then why does the document spend so much time on them?
5. What does section 10.3 specify? As far as I can tell, it just says 
that the answer can be some arbitrary piece of RDF. OK, but who 
decides what is in that RDF?
6. There are several alternative forms for the answer to a SELECT 
query. Who decides what form the answer will take? Can the query 
specify this? How? If not, how can a querying app know how to process 
the answer?

-------

Pat

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Received on Tuesday, 7 December 2004 04:53:56 GMT

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