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Re: today's SPARQL agenda

From: Birte Glimm <birte.glimm@uni-ulm.de>
Date: Tue, 20 Mar 2012 15:11:48 +0100
Message-ID: <CABt65OcVUqP_sO7hBnuiBXF67s1ypgpjFWODFuBXuWgX7OS07g@mail.gmail.com>
To: Andy Seaborne <andy.seaborne@epimorphics.com>
Cc: Steve Harris <steve.harris@garlik.com>, public-rdf-dawg@w3.org
Well, one could also say that DISTINCT can only be put around the
complete path, e.g.,
{ ?X :a/DISTINCT(:c*)/:b*  ?Y } is invalid, but
{ ?X DISTINCT(:a/:c*/:b*)  ?Y } is ok

Birte

On 20 March 2012 15:09, Andy Seaborne <andy.seaborne@epimorphics.com> wrote:
>
>
> On 20/03/12 13:48, Steve Harris wrote:
>>
>> Though I haven't implemented it, so there's a lot of guesswork going on, I
>> don't think I agree.
>>
>> (2) adds extra syntax, and allows for a mixture of approaches in one path.
>
>
> So does just DISTINCT(path) if I understand it:
> e.g.
>
> { ?X :a/DISTINCT(:c*)/:b*  ?Y }
>
>        Andy
>
>
>
>> My preferred implementation, if both were supported, would be to
>> have
>
> one counting, and one non-counting implementation and handoff the the
> appropriate one - this generally makes optimisations easier. c.f.
> DISTINCT/REDUCED v's not queries.
>>
>>
>> - Steve
>>
>> On 2012-03-20, at 10:48, Andy Seaborne wrote:
>>
>>> Lee - Excellent summary.
>>>
>>> A small point:
>>>
>>> The implementation issues of (3) are as (2) because
>>> DISTINCT(path*) is non-counting path*.  It's currently mentioned in the
>>> editors working draft.  We could even define it that way but I have
>>> currently singled out so we can help implementer by giving an algorithm
>>> which does significantly better than distinct-of-counting-path.
>>>
>>>        Andy
>>>
>>> On 20/03/12 05:01, Lee Feigenbaum wrote:
>>>>
>>>> Please note that the call today is still one hour earlier for folks not
>>>> in the US.
>>>>
>>>> Sorry for the late agenda.
>>>>
>>>> Let's attack the property paths issue today and see if we have any
>>>> consensus on how to proceed.
>>>>
>>>> Our options that we need to choose from are (I've tried to summarize
>>>> pros (+) and cons (-) below, but apologize if I've mis-represented or
>>>> mis-characterized anything):
>>>>
>>>> 1) Leave as is, no change
>>>> + Does not require a new last call
>>>> + Does not open up any potential _new_ issues from aspects of new
>>>> design(s)
>>>> - Almost surely results in a formal objection from the various
>>>> commenters about the counting property path execution complexity issue
>>>> - Potentially hamstrings some use cases of property paths, depending on
>>>> whether all non-counting pp instances can be rewritten as SELECT
>>>> DISTINCT subqueries
>>>>
>>>>
>>>> 2) Add DISTINCT(path) and {+}/{*} operators
>>>> + Addresses the commenters' concerns (as per informal discussions with
>>>> some of them offlist)
>>>> + Gives query authors significant expressivity in choosing the path
>>>> counting semantics vs. performance tradeoff they want
>>>> - Requires a new last call
>>>> - Raises the burden to implement property paths
>>>> - New design may have unknown interactions between counting and
>>>> non-counting operators in the same path
>>>>
>>>>
>>>> 3) Add DISTINCT(path) only
>>>> + Addresses the commenters' concerns (as per informal discussions with
>>>> some of them offlist)
>>>> + Gives query authors some expressivity in choosing the path counting
>>>> semantics vs. performance tradeoff they want
>>>> - Requires a new last call
>>>> - Raises the burden to implement property paths (but not as much as #2)
>>>>
>>>>
>>>> 4) Add {+}/{*} counting/not-counting operators only
>>>> + Gives query authors significant expressivity in choosing the path
>>>> counting semantics vs. performance tradeoff they want
>>>> - Requires a new last call
>>>> - Raises the burden to implement property paths (but not as much as #2)
>>>> - Likely results in a formal objection from the various commenters about
>>>> the counting property path execution complexity issue (based on offlist
>>>> discussion of this option)
>>>> - New design may have unknown interactions between counting and
>>>> non-counting operators in the same path
>>>>
>>>> 5) Mark property paths as non-normative
>>>> +/- Not sure if this requires a new last call
>>>> + Lowers implementation burden
>>>> - Removes a significant feature from SPARQL 1.1 Query
>>>> - May lead to formal objections within the working group
>>>>
>>>> Lee
>>>>
>>>
>>
>



-- 
Jun. Prof. Dr. Birte Glimm            Tel.:    +49 731 50 24125
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Received on Tuesday, 20 March 2012 14:12:23 GMT

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