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Re: Another attempt...

From: Andrew Newman <andrewfnewman@gmail.com>
Date: Thu, 20 Mar 2008 08:04:57 +1000
Message-ID: <2db5a5c40803191504u15a4b0cam3a0631c9767e34fe@mail.gmail.com>
To: "Lee Feigenbaum" <lee@thefigtrees.net>
Cc: "Richard Newman" <rnewman@twinql.com>, andy.seaborne@hp.com, "Arjohn Kampman" <arjohn.kampman@aduna-software.com>, "public-rdf-dawg-comments@w3.org" <public-rdf-dawg-comments@w3.org>

On 19/03/2008, Lee Feigenbaum <lee@thefigtrees.net> wrote:
> Andrew Newman wrote:
> This is still unclear to me :) First of all, what dataset are you
>  proposing these queries be evaluated against? An empty default graph or
>  a default graph with triples? Are you saying that you believe that the
>  SPAQL Recommendation specifies that both of these queries should return
>  an empty solution set ({}) or are you saying that you acknowledge that
>  it doesn't but wish that it did?
>

This isn't the usual "bug report".  I'm trying to say a whole class of
queries (any queries) that involve the empty graph pattern {} is
wrong.  So it doesn't matter what the data set is.

>  > The results don't make sense with respect to JOIN identity (which is
>  > defined in the SPARQL specification).  Unless SPARQL is creating its
>  > own algebra (if it is it has a lot of explaining to do - which I'm
>  > happy to read) and is ignoring existing set and/or bag algebra then
>  > the current results being returned by most/all SPARQL implementations
>  > is wrong.
>
>
> Again, are you saying wrong in the sense of:
>
>  1) the implementations do not abide by the SPARQL specification, or
>  2) the implementations abide by the specification, which is not the
>  results you'd desire to see?
>

So while the specification has gone a long way to try and be enough to
create an implementation by itself I don't think it's quite there yet.
 There's pre-requisite knowledge that is not in the specification.

In ARQ and other implementations (because it's not clear in the
specification and I think you said it's not in a test) JOIN and UNION
identity follows integer algebra - this isn't really clear in the
specification - I had assumed it would follow set/bag algebra.  I'm
arguing that following integer algebra doesn't make sense for a query
language.

> OK, thanks. It sounds like you are asking for changes to the SPARQL
>  syntax, algebra, and/or specification. The W3C membership endorsed
>  SPARQL as a Recommendation in January, and the Working Group is not
>  actively pursuing the design of the language (either the syntax, the
>  algebra, or the document) at this time. We are collecting errata
>  (mistakes in the specification, usually expressible as test cases for
>  which the specification's demands do not match the WG's intentions) and
>  feedback for future activity on SPARQL by the DAWG or other working groups.
>

I'm not sure the specification is normative wrt to the behaviour of
UNION and {}.  Adding a test and making it clear that what the
identity is would make it normative I guess.
Received on Wednesday, 19 March 2008 22:05:40 GMT

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