Chatlog 2009-08-11

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13:47:31 <RRSAgent> RRSAgent has joined #sparql
13:47:31 <RRSAgent> logging to http://www.w3.org/2009/08/11-sparql-irc
13:47:33 <trackbot> RRSAgent, make logs world
13:47:33 <Zakim> Zakim has joined #sparql
13:47:35 <trackbot> Zakim, this will be 77277
13:47:35 <Zakim> ok, trackbot; I see SW_(SPARQL)10:00AM scheduled to start in 13 minutes
13:47:36 <trackbot> Meeting: SPARQL Working Group Teleconference
13:47:36 <trackbot> Date: 11 August 2009
13:47:40 <LeeF> Zakim, this will be sparql
13:47:40 <Zakim> ok, LeeF; I see SW_(SPARQL)10:00AM scheduled to start in 13 minutes
13:47:42 <LeeF> Chair: LeeF
13:47:45 <LeeF> Scribe: SimonS
13:47:47 <KjetilK> KjetilK has joined #sparql
13:47:47 <LeeF> Scribenick: SimonS
13:48:01 <LeeF> Regrets: IvanH, pgearon, AndyS
13:48:24 <LeeF> Agenda: http://www.w3.org/2009/sparql/wiki/Agenda-2009-08-11
13:48:30 <LeeF> LeeF has changed the topic to: Agenda - http://www.w3.org/2009/sparql/wiki/Agenda-2009-08-11
14:06:23 <LeeF> zakim, who's here?
14:06:23 <Zakim> On the phone I see kasei (muted), LeeF, SteveH, AlexPassant, john-l, AxelPolleres, kjetilk (muted), Orri, LukeWM, bglimm, Chimezie_Ogbuji (muted), SimonS, Prateek, iv_an_ru, EricP
14:06:26 <Zakim> On IRC I see Prateek, chimezie, bglimm, SimonS, KjetilK, Zakim, RRSAgent, LukeWM, AxelPolleres, SteveH, LeeF, karl, john-l, iv_an_ru, kjetil, AlexPassant, trackbot, kasei, ericP
14:07:00 <SimonS> LeeF: Topics for today are Aggregate design and discovering service descriptions
14:07:23 <LeeF> topic: admin
14:07:30 <LeeF> PROPOSED: Approve minutes at http://www.w3.org/2009/sparql/meeting/2009-08-04
14:07:53 <bglimm> +1
14:08:07 <LeeF> RESOLVED: Approve minutes at http://www.w3.org/2009/sparql/meeting/2009-08-04
14:08:27 <LeeF> Next meeting: 2009-08-18 @ 15:00 BST / 10:00 EDT, SimonKJ to scribe
14:08:34 <bglimm> Next week I am on holiday
14:08:41 <LeeF> http://www.w3.org/2009/sparql/wiki/Vacation_List
14:08:51 <LeeF> regrets next week: bglimm, orri
14:09:42 <LeeF> wiki page for next F2F http://www.w3.org/2009/sparql/wiki/F2F2
14:10:08 <SimonS> LeeF: F2F 1st week of November in Santa Clara. 
14:10:09 <SteveH> $50/day
14:10:52 <SimonS> ... Please indicate your attendance on the Wiki
14:11:10 <chimezie> Zakim, unmute me
14:11:10 <Zakim> Chimezie_Ogbuji should no longer be muted
14:11:29 <KjetilK> q+
14:11:29 <chimezie> Good question, I don't know off head (will need to chew on that).
14:11:37 <chimezie> whoops
14:11:50 <SimonS> LeeF: SPARQL group meeting Monday and Tuesday.
14:12:06 <KjetilK> ack me
14:12:12 <LeeF> ack kjetilk
14:12:31 <SimonS> KjetilK: how about a split meeting with video conferencing?
14:12:36 <bglimm> +1 to KjetilK
14:12:39 <ericP> q+ to talk about challenges
14:12:44 <ericP> q-
14:12:53 <ericP> q+ to talk about tech challenges re: vid conf
14:13:05 <SimonS> LeeF: might be possible, but huge time difference, European side needs to host night owls.
14:13:36 <bglimm> I would fly just for the 2 days and the jet-lag would kill me, I rather stay up late here
14:13:45 <KjetilK> Zakim, mute me
14:13:45 <Zakim> kjetilk should now be muted
14:13:53 <bglimm> I could probably organize some video conferencing here
14:14:47 <SimonS> EricP: point of the meeting also is to interact with other groups, which means we need video conferencing on site, which is prohibitively expensive.
14:15:05 <SimonS> LeeF: Unlikely that we will have video conferencing.
14:15:19 <SimonS> ... phone will be available, though.
14:15:57 <SteveH> can we chivvy people to say whether they're going or not?
14:16:03 <SteveH> I have to decide soon
14:16:09 <iv_an_ru> Which Ivan?
14:16:13 <ericP> nothing new from HCLS or XQuery
14:16:15 <SimonS> topic: Liaisons
14:17:01 <SimonS> Orri: nothing new from RDB2RDF
14:17:14 <AxelPolleres> no news from RIF (teleconfs irregular, there is one today, so I will know more next week)
14:17:35 <SimonS> Orri: talk about it at the F2F.
14:17:42 <SimonS> topic: actions
14:17:39 <LeeF> open actions - http://www.w3.org/2009/sparql/track/actions/open
14:17:52 <LeeF> trackbot, close ACTION-66
14:17:52 <trackbot> ACTION-66 Draft aggregates closed
14:20:09 <AxelPolleres> 71 is done from my side in the sense that rif and rdb2rdf are informed.
14:20:07 <LeeF> topic: Aggregates
14:20:24 <LeeF> draft of aggregate design at http://www.w3.org/2009/sparql/wiki/Design:Aggregate
14:21:29 <SimonS> chimezie: First draft, some issues regarding sets vs multi-sets
14:21:39 <SimonS> ... do we need specific restrictions?
14:21:48 <SimonS> ... how to deal with DISTINCT?
14:21:55 <LeeF> open issues at http://www.w3.org/2009/sparql/wiki/Design:Aggregate#Status
14:22:22 <SimonS> ... seems we want to have variables associated with result of aggregates, so we always need AS
14:22:44 <SimonS> ... tried to describe algebra extension.
14:23:20 <SimonS> ... Start with groups function
14:23:56 <SimonS> ... starting with grouped variables. 
14:24:39 <SimonS> ... function partitions takes solution set and extracts unique n-tuples, which are partitions of the solution set
14:24:51 <AxelPolleres> q+ to ask about whether bnodes should be considered nasty or not
14:25:15 <LeeF> ack ericp
14:25:16 <Zakim> ericP, you wanted to talk about tech challenges re: vid conf
14:25:20 <SimonS> ... Aggregation then computes the actual aggregate.
14:25:29 <SimonS> ... now need test cases
14:26:21 <AxelPolleres> ack me
14:26:21 <Zakim> AxelPolleres, you wanted to ask about whether bnodes should be considered nasty or not
14:26:59 <ericP> q+ to propose we stay with a graph semantics
14:27:02 <SimonS> AxelPolleres: Are BNodes in the solution set an issue? e.g. count is difficult, if BNodes are treated as existentials
14:27:13 <SimonS> ... most implementations treat them as constants, though.
14:27:56 <bglimm> I agrre in that blank nodes in our reasoner (OWL direct semantics) are not the same as constants
14:28:00 <SimonS> Orri: We treat them as constants, sometimes owl:sameAs semantics is applied
14:28:06 <LeeF> ack ericP
14:28:06 <Zakim> ericP, you wanted to propose we stay with a graph semantics
14:28:26 <SimonS> EricP: Language should stay a graph based language.
14:28:31 <AxelPolleres> similar with "!=" which is currently "not known to be equal"
14:29:14 <SimonS> LeeF: treat as in equals in filters
14:29:25 <SimonS> ... might need to look at this again for entailment regimes.
14:29:38 <LeeF> ISSUE: How do other entailment regimes interact with aggregate grouping vis a vis blank nodes?
14:29:38 <trackbot> Created ISSUE-34 - How do other entailment regimes interact with aggregate grouping vis a vis blank nodes? ; please complete additional details at http://www.w3.org/2009/sparql/track/issues/34/edit .
14:30:25 <SimonS> Orri: Guess, you can do expressions of aggregates
14:31:46 <LeeF> for the record, extensibility of aggregate functions is an open issue http://www.w3.org/2009/sparql/track/issues/15
14:31:48 <SimonS> ... are user defined aggregates in scope, but we might need syntax restrictions?
14:32:18 <SimonS> LeeF: we already have issue for extensions in aggregate functions
14:32:22 <ericP> am fiddling with grammar (has S/R errors) -- http://www.w3.org/2005/01/yacker/uploads/SPARQL_Aggregate?lang=perl
14:32:22 <Zakim> -SimonS
14:32:59 <Zakim> +??P30
14:33:08 <SimonS> Zakim, ??P30 is me
14:33:08 <Zakim> +SimonS; got it
14:33:46 <LeeF> LeeF: can aggregate functions take multiple arguments?
14:34:00 <LeeF> Chimezie: As long as all variables are part of gorup keys, should be ok, not sure if SQL aggregate functions do this at all
14:34:05 <LeeF> Orri: there are a few like diverse_regression
14:34:37 <ericP> ok, no S/Rs in http://www.w3.org/2005/01/yacker?name=SPARQL_Aggregate&replace=1&lang=perl
14:35:11 <SimonS> chimezie; issues with multi sets. Do not require uniqueness. however, Aggregates do for partitioning.
14:35:49 <SimonS> EricP: Algebra does not have ordering, but aggregates need them. Current algebra should work.
14:35:58 <SimonS> Orri: Why do aggregates require ordering?
14:36:09 <SimonS> EricP: Not always, but might make sense.
14:36:28 <chimezie> SteveH did have an example on the SubSelect design wiki asking about ordering and aggregation (working together)
14:36:35 <SimonS> Orri: For user defined aggregates we have a flag for that, but usually it is not neccessary.
14:36:58 <SimonS> ... should not be an issue, if we do not specify extension syntax
14:37:18 <LeeF> q?
14:37:35 <SimonS> iv_an_ru: also benefits for parallelization then.
14:37:51 <chimezie> Zakim, who is here?
14:37:51 <Zakim> On the phone I see kasei (muted), LeeF, SteveH, AlexPassant, john-l, AxelPolleres, kjetilk (muted), Orri, LukeWM, bglimm, Chimezie_Ogbuji, Prateek, iv_an_ru, EricP, SimonS
14:37:55 <Zakim> On IRC I see Prateek, chimezie, bglimm, SimonS, KjetilK, Zakim, RRSAgent, LukeWM, AxelPolleres, SteveH, LeeF, karl, john-l, iv_an_ru, kjetil, AlexPassant, trackbot, kasei, ericP
14:38:20 <SimonS> LeeF: do we need test case, that needs ordering?
14:38:30 <SimonS> EricP: same as for SubSelect.
14:38:48 <SimonS> LeeF: Last week we had consensus to discard ordering for subqueries.
14:39:12 <SimonS> Orri: ORDER BY allowed?
14:39:37 <SimonS> LeeF: yes, needed for slicing for example, but when combined with parent query, order is lost.
14:40:07 <SimonS> LeeF: what specific aggregate functions to include?
14:40:10 <AxelPolleres> any slicing in subqueries potentially introduces non-determinism, but well, I guess that was discussed?
14:40:17 <SimonS> ... discuss tios on the mailing list.
14:40:19 <ericP> chimezie, do you know of a grammar proposal for  SELECT ?foo AS ?bar  which i could inject tinot the SPARQL_Aggregate grammar?
14:40:46 <SimonS> LeeF: How to apply REDUCED / DISTINCT? Afterwards?
14:41:04 <SimonS> chimezie: if done afterwards, everything should be fine.
14:41:05 <ericP> ahh, it was in your proposal
14:41:14 <SimonS> Orri: grouped columns are distinct anyway.
14:42:01 <SimonS> Orri: Can we have DISTINCT in aggregate expressions?
14:42:16 <SimonS> ... e.g. SELECT COUNT(DISTINCT ?X)
14:42:33 <LeeF> ISSUE: Can aggregate functions take DISTINCT as an argument a la SELECT COUNT(DISTINCT ?X)?
14:42:33 <trackbot> Created ISSUE-35 - Can aggregate functions take DISTINCT as an argument a la SELECT COUNT(DISTINCT ?X)? ; please complete additional details at http://www.w3.org/2009/sparql/track/issues/35/edit .
14:42:55 <LukeWM> q+ to ask about HAVING
14:43:13 <LeeF> ack LukeWM
14:43:13 <Zakim> LukeWM, you wanted to ask about HAVING
14:43:34 <SimonS> LukeWM: does HAVING cause issues?
14:43:43 <SimonS> Orri: HAVING is save. 
14:44:02 <SimonS> ... can be done in nested query.
14:44:06 <LeeF> q?
14:44:43 <kasei> we had talked earlier about using FILTER instead of HAVING (not introducing new terms for roughly the same thing)
14:44:53 <SteveH> yes, reusing FILTER would makesense
14:45:06 <SimonS> chimezie: should be easy to add to the proposal for completeness' sake.
14:45:46 <LeeF> ACTION: Chimezie to continue forward with aggregates w.r.t test cases, HAVING/FILTER clause, ISSUE-35, ...
14:45:46 <trackbot> Created ACTION-79 - Continue forward with aggregates w.r.t test cases, HAVING/FILTER clause, ISSUE-35, ... [on Chimezie Ogbuji - due 2009-08-18].
14:46:23 <LeeF> topic: service description
14:47:22 <LeeF> -> http://lists.w3.org/Archives/Public/public-rdf-dawg/2009JulSep/0139.html
14:47:26 <SimonS> LeeF: Most important question is discovery mechanism. We have >= 8 proposals.
14:48:54 <SimonS> ... drop proposal 3 - Well known location.
14:49:02 <SimonS> ... general agreement on this.
14:49:23 <SimonS> ... drop 5 - Query as well.
14:49:31 <AxelPolleres> is "DESCRIBE <.>" also meant as a suboption of Opt 4?
14:49:42 <SimonS> ... EricP likes it, but noone else.
14:50:32 <SimonS> ... some objections to 6: prefer discovery via the endpoint instead of via the query.
14:52:07 <ericP> chimezie, http://tinyurl.com/SPARQL-sum shows that your example query works with the grammar you supplied (modulo AggregateFunc which I added)
14:52:16 <SimonS> ... issue with option 7 without conneg is that existing implementations might have webpages at endpoint URI
14:52:38 <SimonS> ... proposal 8: do get with some special operation
14:52:43 <chimezie> ericP: thanks
14:53:00 <ericP> feel free to fiddle with the grammar
14:53:10 <ericP> (note [Edit this grammar])
14:53:11 <SimonS> ... is anyone NOT happy with using an approach based on the endpoint rather than the query?
14:53:18 <kasei> eh
14:53:56 <kasei> Zakim, unmute me
14:53:56 <Zakim> kasei should no longer be muted
14:54:10 <SimonS> EricP: might be nice to be able to query endpoint descriptions, but could solve that differently.
14:54:46 <AxelPolleres> q+
14:54:47 <SimonS> kasei: favors conneg
14:55:08 <LukeWM> np
14:55:17 <kasei> Zakim, mute me
14:55:17 <Zakim> kasei should now be muted
14:55:21 <LeeF> ack AxelPolleres
14:55:34 <SimonS> AxelPolleres: What was objection to option 4?
14:55:53 <SimonS> LeeF: restricts possible datasets and URIs
14:55:59 <kasei> and that describe doesn't always return the same things...
14:56:02 <ericP> q+ to ask how i find for instance, what VoID description it has in opt 4
14:56:21 <SimonS> LeeF: same for DESCRIBE <> as it is just a shortcut
14:56:28 <LeeF> ack ericP
14:56:28 <Zakim> ericP, you wanted to ask how i find for instance, what VoID description it has in opt 4
14:57:12 <SteveH> you can still do FROM <endpoint> .... on stores that support it
14:57:13 <SimonS> EricP: that also means optimization becomes more difficult than just serving a void description.
14:57:39 <SimonS> Orri: You would usually ask for the whole graph once.
14:58:20 <SimonS> EricP: imagine void, void* etc, so guessing the best representation is a burden on the endpoint
14:59:36 <SimonS> Orri: don't want to do many round trips with lots of short queries. Retrieve full description once, then do postprocessing locally.
14:59:59 <SimonS> EricP: But we might be interested in certain aspects of the description only.
15:00:09 <AxelPolleres> q+ to ask about the relative or absolute description in the protocol based options 
15:00:22 <kasei> ericP's point, I think, supports conneg or a simple GET mechanism so that you *could* point a SPARQL query at the SD if you wanted.
15:00:24 <LeeF> zakim, close the queue
15:00:24 <Zakim> ok, LeeF, the speaker queue is closed
15:01:01 <SimonS> Orri: We might say in the void description that the description is queryable, and where.
15:01:24 <LeeF> ack AxelPolleres
15:01:24 <Zakim> AxelPolleres, you wanted to ask about the relative or absolute description in the protocol based options
15:02:07 <SimonS> AxelPolleres: option 1 is just about returning a link to the service description, i.e. two GETs are neccessary, while the others are one GET only.
15:02:13 <SimonS> LeeF: that is right.
15:02:32 <AxelPolleres> 2 GETs for getting to the service description seems a bit awkward to me, personally.
15:02:59 <LeeF> PROPOSED: Service description discovery should be based on an operation performed against a SPARQL endpoint, ruling out options 3,4,5,6 in http://lists.w3.org/Archives/Public/public-rdf-dawg/2009JulSep/0139.html
15:03:51 <AxelPolleres> need to get something clear: does it mean we agree that QUERYING the service description should NOT necessarily be allowed on the very endpoint?
15:04:02 <Zakim> -iv_an_ru
15:04:22 <SimonS> I'd say not required.
15:04:43 <SteveH> to be convinced I'd need to be shown that it works, not that it meets some usecases
15:05:03 <SimonS> EricP: Could do use cases for querying. Would that be worth while?
15:05:13 <SteveH> you can still do FROM <endpoint> .... on stores that support it
15:05:30 <SimonS> Orri: Propose to include in the endpoint based description link to the queryable version
15:06:18 <kasei> option 7 gives you queryability for free with a FROM clause.
15:07:03 <SimonS> LeeF: discussion closed, please continue on the mailing list. Continue discussion next week
15:07:10 <LeeF> ACTION: Orri to send a compromise proposal to the mailing list
15:07:11 <trackbot> Created ACTION-80 - Send a compromise proposal to the mailing list [on Orri Erling - due 2009-08-18].
15:07:44 <Zakim> -Chimezie_Ogbuji
15:07:44 <LeeF> Adjourned.
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