Comments on SPARQL 1.1 WD 20091022

[Leigh Dodds-3]

Hi,

Here are some personal comments/questions on the 22/10/2009 WD of SPARQL 1.1.

* Example in Section 2. I don't think the project expression conforms
with grammar shown latter in the doc; missing brackets? I know this is
still up for discussion, but thought I'd point it out

* Section 2, Syntax. re: the note about using FILTER instead of
HAVING. Assuming I'm reading the comment correctly, I think for
readability purposes its better to have a separate keyword (HAVING)
rather than re-use the FILTER keyword. I think its clearer that there
are different constraints (i.e. aggregates allowed or not) on the
expression, and retains similarity with SQL.

* Section 3. Text above example query is wrong, I think it should
ready "from all the people that Alice knows", not "that know Alice".

* Section 4. What is the rationale for including both a FILTER and a
graph pattern operator for EXISTS/NOT EXISTS? If there are benefits in
terms of expressivity or ease of implementation it would be good to be
able to call these out in the specification.

* Section 4. The NOT EXISTS and EXISTS graph pattern operators are
described as "applying only to variables defined earlier in the
pattern". What does "earlier" mean if a SPARQL processor can re-order
the statements for optimization purposes? Does use of those operators
have some impact on an implementations ability to do that?

Cheers,

L.

--
Leigh Dodds
Programme Manager, Talis Platform
Talis
leigh.dodds@...
http://www.talis.com

[Andy Seaborne]

On 24/10/2009 14:09, Leigh Dodds wrote:
Leigh,

Thank you for your comments.

This first published working draft contains the new areas for query that
the working group is progressing.  The material will be integrated with
the the previous version of the query language to produce a single, new
document for SPARQL 1.1 Query.

Things may be a little rough in this first draft ...

Leigh Dodds wrote:
  > Hi,
  >
  > Here are some personal comments/questions on the 22/10/2009 WD of
SPARQL 1.1.
  >
  > * Example in Section 2. I don't think the project expression conforms
  > with grammar shown latter in the doc; missing brackets? I know this is
  > still up for discussion, but thought I'd point it out

Yes - it's not consistent.  The WG had not reached a conclusion on the
exact syntax at the time of publication.

  > * Section 2, Syntax. re: the note about using FILTER instead of
  > HAVING. Assuming I'm reading the comment correctly, I think for
  > readability purposes its better to have a separate keyword (HAVING)
  > rather than re-use the FILTER keyword. I think its clearer that there
  > are different constraints (i.e. aggregates allowed or not) on the
  > expression, and retains similarity with SQL.
  >
  > * Section 3. Text above example query is wrong, I think it should
  > ready "from all the people that Alice knows", not "that know Alice".

Agreed.

  >
  > * Section 4. What is the rationale for including both a FILTER and a
  > graph pattern operator for EXISTS/NOT EXISTS? If there are benefits in
  > terms of expressivity or ease of implementation it would be good to be
  > able to call these out in the specification.

If the working group decides to allow EXISTS/NOT EXISTS in FILTERs, then
there will be a example to illustrate the point.

  > * Section 4. The NOT EXISTS and EXISTS graph pattern operators are
  > described as "applying only to variables defined earlier in the
  > pattern". What does "earlier" mean if a SPARQL processor can re-order
  > the statements for optimization purposes? Does use of those operators
  > have some impact on an implementations ability to do that?

It's loose wording to discuss the scoping of variables.  "earlier" means
the pattern to the left or above of the NOT EXISTS.

  >
  > Cheers,
  >
  > L.

    Andy
    on behalf of the SPARQL Working Group