15:53:33 <RRSAgent> RRSAgent has joined #RDB2RDF
15:53:33 <RRSAgent> logging to http://www.w3.org/2012/05/15-RDB2RDF-irc
15:53:49 <Ashok> zakim, this will be rdb2rdf
15:53:49 <Zakim> ok, Ashok; I see SW_RDB2RDF()12:00PM scheduled to start in 7 minutes
15:54:00 <Ashok> chair: Ashok
15:54:15 <Ashok> meeting: RDB2RDF Teleconference
15:58:30 <nunolopes> nunolopes has joined #rdb2rdf
15:58:45 <Zakim> SW_RDB2RDF()12:00PM has now started
15:58:52 <Zakim> + +1.781.273.aaaa
15:59:02 <MacTed> Zakim, aaaa is OpenLink_Software
15:59:02 <Zakim> +OpenLink_Software; got it
15:59:08 <MacTed> Zakim, OpenLink_Software is temporarily me
15:59:08 <Zakim> +MacTed; got it
15:59:22 <dmcneil> dmcneil has joined #RDB2RDF
16:00:05 <Zakim> +Ashok_Malhotra
16:00:15 <Zakim> + +1.314.395.aabb
16:00:26 <Ashok> zakim, who is on the phone?
16:00:26 <Zakim> On the phone I see MacTed, Ashok_Malhotra, +1.314.395.aabb
16:00:45 <Zakim> +??P26
16:00:56 <nunolopes>  Zakim, ??P26 is me
16:01:12 <cygri> zakim, mhausenblas is temporarily me
16:01:12 <Zakim> sorry, cygri, I do not recognize a party named 'mhausenblas'
16:01:14 <Zakim> + +3539149aacc
16:01:18 <juansequeda> juansequeda has joined #rdb2rdf
16:01:24 <cygri> zakim, aacc is me
16:01:24 <Zakim> +cygri; got it
16:01:32 <Zakim> + +575737aadd
16:01:38 <juansequeda> Zakim, aadd is me
16:01:38 <Zakim> +juansequeda; got it
16:02:14 <Ashok> present: Richard, David, Ted, Ashok, Juan, Nuno
16:02:41 <Ashok> regrets: Eric, Ivan, Michael, Boris
16:02:48 <cygri> zakim, nunolopes is with me
16:02:48 <Zakim> +nunolopes; got it
16:03:13 <Zakim> -??P26
16:03:30 <Ashok> zakim, pick a victim
16:03:30 <Zakim> Not knowing who is chairing or who scribed recently, I propose +1.314.395.aabb
16:03:35 <dmcneil> I can do it
16:03:50 <Ashok> scribenick: David
16:03:50 <MacTed> Zakim, aabb is dmcneil
16:03:50 <Zakim> +dmcneil; got it
16:03:52 <joerg> joerg has joined #RDB2RDF
16:03:53 <MacTed> Zakim, who's here?
16:03:53 <Zakim> On the phone I see MacTed, Ashok_Malhotra, dmcneil, cygri, juansequeda
16:03:54 <Zakim> cygri has cygri, nunolopes
16:03:54 <Zakim> On IRC I see joerg, juansequeda, dmcneil, nunolopes, RRSAgent, Zakim, Ashok, cygri, LeeF, MacTed, betehess, trackbot, ericP
16:04:09 <MacTed> scribenick: dmcneil
16:04:27 <Ashok> Topic:  1. Admin PROPOSAL: Accept the minutes of last meeting http://www.w3.org/2012/05/08-RDB2RDF-minutes.html 
16:05:06 <dmcneil> minutes accepted
16:05:45 <Zakim> +??P6
16:05:47 <Ashok> Topic: 2. Implementability for tables w/o primary key 
16:06:04 <dmcneil> where we were: we spoke last time about what to do
16:06:16 <Zakim> + +1.603.897.aaee
16:06:40 <dmcneil> one thing we spoke about was writing some text describing the disconnect between the DM and the R2RML
16:07:04 <dmcneil> there was a sense that we should bite the bullet and address this issue by extending R2RML
16:07:13 <dmcneil> Richard & Eric wrote up a proposal
16:07:23 <cygri> proposal was here: http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2012May/0075.html
16:07:31 <dmcneil> and he thought we had reasonable support for the proposal
16:07:57 <dmcneil> but, then David argued that we should do nothing because you can use vendor-specific SQL in R2RML to accomplish the goal of mapping tables without primary keys
16:08:02 <Zakim> + +1.603.897.aaff
16:08:38 <cygri> dmcneil: core issue is that vendor-specific sql is needed
16:08:54 <cygri> ... i argue best approch is to do it with views
16:09:07 <cygri> ... because that puts the burden on the DM implementer
16:09:18 <Ashok> David:  I think the problem can be done with views, so no change is needed
16:10:09 <cygri> ... whatever SQL query would be needed to actually compute the DM, just write that into a view
16:11:00 <juansequeda> Which vender does not have a generate_series/rownum function?
16:11:10 <cygri> ... example, postgres has a function for computing sequences. same with other DBs
16:11:33 <cygri> ... then the usual R2RML mechanisms can be used to generate blank nodes
16:11:45 <Ashok> q?
16:12:15 <dmcneil> +q
16:12:25 <cygri> q+
16:12:51 <cygri> ashok: so we need to find out whether all the DBs have some mechanism like that?
16:12:53 <Souri_> Souri_ has joined #RDB2RDF
16:13:11 <Ashok> Need to find out whether SQL Server and DB2 has such a function
16:13:23 <cygri> dmcneil: suppose DB2 doesn't have it. how does hiding this behind RowBlankNode help then?
16:14:52 <dmcneil> cygri: once concern is that the way R2RML is defined in terms of core SQL 2008
16:15:10 <dmcneil> ... we acknowledged that people would use vendor specific SQL
16:15:40 <dmcneil> ... the way we dealt with that is that if you wnat to use db specific dialect of SQL then you are defining a vendor specific extension of R2RML
16:15:44 <Ashok> zakim, who is on the phone?
16:15:44 <Zakim> On the phone I see MacTed, Ashok_Malhotra, dmcneil, cygri, juansequeda, ??P6, +1.603.897.aaee, +1.603.897.aaff
16:15:47 <Zakim> cygri has cygri, nunolopes
16:16:03 <dmcneil> ... taking that to it's logical conclusion, then we are saying that R2RML as specified cannot be used to implement the Direct Mapping
16:16:24 <dmcneil> ... since the general assumption is it is not possible to support this case with generic SQL
16:16:35 <dmcneil> ... so the user must immediately extend R2RML for this case
16:16:38 <dmcneil> +q
16:16:52 <dmcneil> ... this is not a particularly pleasant situation
16:16:58 <dmcneil> ashok: neither of this is perfect
16:17:04 <MacTed> q+
16:17:49 <Ashok> ack next
16:17:54 <Ashok> ack next
16:18:34 <dmcneil> dmcneil: I think that is a specious argument, because we expect that most mappings will have vendor-specific SQL in them
16:18:55 <dmcneil> cygri: correction, by default embedded SQL is expected to be SQL CORE 2008
16:19:21 <dmcneil> macted: if we did that (not sure what "that" references) it was a serious mistake
16:19:43 <cygri> http://www.w3.org/2001/sw/rdb2rdf/r2rml/#conformance
16:19:47 <Ashok> This specification defines R2RML for databases that conform to Core SQL 2008, as defined in ISO/IEC 9075-1:2008 [SQL1] and ISO/IEC 9075-2:2008 [SQL2]. Processors and mappings may have to deviate from the R2RML specification in order to support databases that do not conform to this version of SQL.
16:20:27 <dmcneil> from the spec "The absence of a SQL version identifier indicates that no claim to Core SQL 2008 conformance is made."
16:20:52 <Ashok> ack next
16:20:54 <dmcneil> +q
16:21:26 <dmcneil> MacTed: suggests that he thought we had agreement last week
16:21:32 <dmcneil> discussion of who dissented
16:21:49 <dmcneil> cygri: eric strongly believes that preserving cardinality is important
16:21:59 <dmcneil> macted: let them choose the DM variant that preserves it then
16:22:15 <dmcneil> cygri: the argument was made that the cardinality preserving option is more correct
16:22:29 <dmcneil> ... I argued that that is just an option, implementations are free to implement it
16:22:53 <dmcneil> ... was also ok with putting in warnings about the non-cardinality preserving option
16:23:31 <dmcneil> ... from last week we said if we had more time we would define a way to make this work in R2RML
16:23:54 <dmcneil> ... the point was raised that for backwards compatibility we cannot remove it later
16:24:18 <dmcneil> ... suggested wording that "we might remove this in the future" was not well received
16:24:35 <Seema> Seema has joined #rdb2rdf
16:24:39 <dmcneil> ... also, they don't want options in the DM, just a single monolithic approach
16:24:57 <dmcneil> ashok: last week, we spoke about some text that ivan had crafted
16:25:07 <dmcneil> ... are you speaking about that, or a previous position they has
16:25:10 <dmcneil> s/has/had
16:25:19 <dmcneil> cygri: I am speaking about some text that I drafted
16:25:37 <dmcneil> ... ivan drafted some text proposing no change but saying they are incompatible
16:26:04 <cygri> http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2012May/0054.html
16:26:16 <Ashok> PROPOSAL A: In the DM spec, replace the following text:  [[ If the table has no primary key, the row node is a fresh blank node that is unique to this row. ]]  with this:  [[ If the table has no primary key, the row node is a blank node. Distinct blank nodes MUST be generated for rows with distinct column values. For duplicate rows with identical values, implementations SHOULD generate a fresh blank for each duplicate row (resulting in a non-lean RDF graph [R
16:27:00 <juansequeda> I still support Proposal A :)
16:27:37 <Ashok>  o In the DM, instead of "is intended to provide a default behavior for R2RML: RDB to RDF Mapping Language" say "is intended to provide a default behavior for R2RML: RDB to RDF Mapping Language for tables which have at least one unique key"   o Add to the R2RML document (probably in the intro part): "R2RML implementations are encouraged to provide a default mapping equivalent to the Direct Mapping for tables which have at least one unique key"   o Add a Note 
16:27:44 <MacTed> MacTed has joined #RDB2RDF
16:28:54 <dmcneil> cygri: last week we said we would explore adding something to R2RML
16:29:13 <dmcneil> ... then the objection from david, which i think is reasonable, I can see where he is coming from
16:29:26 <dmcneil> ... did eric come up with a use case?
16:29:27 <cygri> http://www.w3.org/2001/sw/rdb2rdf/wiki/Non-unique_Tables
16:29:35 <dmcneil> ashok: yes, it is on the wiki, but it is a bit complicated
16:31:03 <dmcneil> ashok: do you support one of these two proposals
16:31:27 <dmcneil> dmcneil: i think, that other than doing nothing, adding a rownum column to R2RML is the most interesting
16:31:54 <dmcneil> cygri: the problem with that approach is that it leads too much to a particular implementation
16:32:05 <dmcneil> ... implementations could choose something more efficient than rownum
16:32:42 <dmcneil> ... for example, this mysql query pasted (not sure which query) numbers the rows, but doesn't use rownum
16:33:05 <Souri_> how about rr:genRowId ?
16:33:10 <dmcneil> ... since rownum forces a particular approach that requires the user to spell out what the blank node identifier looks like
16:33:12 <Souri_> q+
16:33:17 <Ashok> In a ROWNUM capable DB, the mapping processor implicitly converts it to the following R2RML mapping (the actual implementation may vary from DB to DB based upon how the equivalent of ROWNUM can be implemented)  <Tmap1> rr:logicalTable [ rr:sqlQuery """ Select ROWNUM AS "rr:rownum", t.* from Wonderland t order by "rr:rownum" """ ] rr:subjectMap [ rr:template "http://Wonderland/my_rownum={\"rr:rownum\"}" ]  We can also say that rr:rownum cannot be used when log
16:33:36 <Ashok> ack next
16:34:35 <Ashok> present+: Souri
16:34:55 <Souri_> present+: Seema
16:34:56 <cygri> A SQL query is a SELECT query in the SQL language that can be executed over the input database. The string must conform to the production <direct select statement: multiple rows> in [SQL2]
16:34:57 <dmcneil> dmcneil: since SQL defaults to not be SQL 2008 in an R2RML view, this means adding an R2RML view by default makes a vendor specific mapping
16:35:20 <dmcneil> cygri: actually the SQL version identifier doesn't affect the processing at all, per the spec
16:37:48 <dmcneil> souri: regarding the rownum discussion
16:37:50 <Ashok> ack next
16:37:57 <dmcneil> ... for every row we need a unique id
16:38:27 <dmcneil> ... if we knew the target database, then we could write vendor-specific SQL
16:38:51 <dmcneil> ... but, if we present that to the user, then the user may not understand that and it is not portable to other database backends
16:39:00 <dmcneil> ... therefore we want a logical representation
16:39:12 <dmcneil> ... if "rownum" has too much meaning with it
16:39:26 <dmcneil> ... then we can use "rowidentifier" or something
16:39:46 <dmcneil> ... this could be used in blank node generation or URI generation
16:40:15 <cygri> q+
16:40:20 <dmcneil> ... we need one R2RML construct, which provides a point of indirection for whatever vendor-specific mechanism it will be translated to
16:40:39 <dmcneil> ashok: isn't the ability to add a column that gets it's values from a function part of SQL-2008?
16:41:06 <dmcneil> souri: not sure, but this is very common
16:41:30 <dmcneil> ashok: so we could add a column in the SQL query that gives distinct numbers
16:41:35 <dmcneil> souri: a sequence generator, right?
16:41:49 <dmcneil> ... in Oracle, access to the sequence generator is a DML operation
16:42:00 <Ashok> q?
16:42:09 <Ashok> ack next
16:42:24 <dmcneil> cygri: regarding souri's point about semantics of the pseudo-rownum column
16:42:31 <dmcneil> ... agree all we need is an identifier
16:42:47 <dmcneil> ... understand that calling it rownum, does not mean it must be literally the db's rownum
16:43:06 <dmcneil> ... just one tiny step from that to the RowBlankNode proposal
16:43:19 <dmcneil> ... we leave it completely up to the implementation what the blank node template it
16:43:30 <dmcneil> +q
16:43:51 <dmcneil> ... since blank node identifiers have no semantics, they just must be unique
16:44:26 <dmcneil> ... so i can't see the usefullness of letting the user put the rownum into a template
16:44:31 <Ashok> ack next
16:45:31 <Zakim> +EricP
16:45:53 <dmcneil> dmcneil: we worked out how regular blank node ids work, we based that on whether the blank node template produces the same value
16:45:59 <Ashok> present+: Eric
16:46:20 <dmcneil> ... would need that same capability for these new RowBlankNode things
16:46:37 <dmcneil> MacTed: the question comes down to doing a dump of the data
16:46:39 <dmcneil> +q
16:46:54 <cygri> q+ to mention jena api
16:48:07 <Ashok> ack next
16:48:09 <Ashok> ack next
16:48:10 <Zakim> cygri, you wanted to mention jena api
16:48:19 <dmcneil> dmcneil: I am talking about within the context of a query, not between queries
16:48:38 <dmcneil> cygri: ted, what you say is completely correct for SPARQL queries
16:48:42 <Zakim> -??P6
16:48:51 <dmcneil> ... can't tell if the blank node ids between queries are the same resource or not
16:48:59 <dmcneil> ... per the spec
16:49:09 <dmcneil> ... but, looking at the jena api
16:49:31 <dmcneil> ... must look at constraints of jena api
16:49:42 <dmcneil> ... which expects blank nodes to have a persistent identity
16:51:04 <dmcneil> ... this leads to the need to go back to the database and graph properties for a specific blank node
16:51:18 <dmcneil> ted: once you go back to the database, you cannot rely on the blank nodes IDs
16:51:20 <dmcneil> yes
16:51:37 <dmcneil> +q
16:52:23 <dmcneil> cygri: the RDF working group has been arguing about this for a year
16:53:26 <dmcneil> several people said they don't want to talk about blank node ID
16:53:31 <dmcneil> dmcneil: this is relevant
16:53:44 <cygri> dmcneil, i believe it is all worked out in the proposal. at least i thought about it hard. i need to answer your email, sorry i didn't get around to do that yet
16:53:59 <dmcneil> ... because we worked out the blank node ID semantics carefully for the existing mechanism, not so much for the new RowBlankNode
16:54:00 <dmcneil> +q
16:54:11 <dmcneil> ashok: we have two options on the table, how to proceed
16:54:19 <Souri_> Is that all the disagreement about? Nothing else?
16:55:08 <dmcneil> dmcneil: there is a third option, let the DM use R2RML views to implement this
16:55:22 <dmcneil> ashok: I like that option, but I thought richard disagreed
16:55:38 <dmcneil> cygri: my position is: it can be done, but it cannot be done in a way that conforms with the spec
16:55:46 <dmcneil> ... because it requires vendor-specific SQL
16:55:54 <dmcneil> ... it is going to be slow, and no way to make it fast
16:56:33 <Ashok> q?
16:59:26 <dmcneil> ashok: some would argue that since SQL is such a sprawling spec, anytime someone writes SQL they are using vendor-specific SQL
17:01:16 <dmcneil> cygri: if the argument is that the DM can be implemented on R2RML, then the question is how?
17:01:44 <dmcneil> dmcneil: the DM is implemented on a specific database, so the DM generates an R2RML view that uses that database's features to implement the DM
17:02:02 <dmcneil> cygri: that leads to very in-efficient implementations
17:02:54 <Souri_> Identical rows: We do not care whether they are assigned Ids <1,2,...,n> or <n,...,2,1> (because their contents are identical)
17:03:38 <dmcneil> cygri: stable identifiers are needed so the next query produces the same identifiers
17:03:44 <dmcneil> macted: you are not going to get it
17:03:54 <dmcneil> ... the database is free to change the ids
17:04:12 <dmcneil> ashok: saying the identifiers are stable is going beyond the spec
17:04:32 <dmcneil> ... three choices:
17:04:40 <dmcneil> ... 1) do nothing
17:04:45 <Souri_> Two rows <a, b, c1> and <a, b,c2> may be assigned Ids _:b1 and _:b2 during one access and _:b2 and _:b1 during another access. Is this acceptable or not?
17:04:55 <dmcneil> ... 2) Richard's proposal
17:05:00 <Souri_> q+
17:05:05 <dmcneil> ... 3) Souri's proposal
17:05:08 <dmcneil> -q
17:05:09 <cygri> souri, yes it is. but if they are _:b3 and _:b4 that's not acceptable
17:05:20 <dmcneil> ... how do we come to agreement?
17:05:37 <dmcneil> macted: do nothing is not an option because currently there is a "must" in there
17:05:45 <dmcneil> cygri: "do nothing" means
17:05:57 <dmcneil> ... DM and R2RML are two entirely separate beasts
17:06:05 <dmcneil> ... just a violation of the basic premise of the DM
17:06:06 <dmcneil> +q
17:06:30 <dmcneil> eric: it could still be the default behavior for all but the case of duplicate keys
17:06:42 <Ashok> ack next
17:06:46 <dmcneil> souri: still trying to understand the requirement
17:06:57 <seema> seema has joined #rdb2rdf
17:07:09 <dmcneil> ... does the blank node ID need to be stable, or can it change?
17:07:27 <dmcneil> cygri: yes, they can be scrambled but they cannot change to a different set of blank node IDs
17:07:34 <dmcneil> macted: what!?
17:07:43 <MacTed> _blank1   a, b, c1
17:07:43 <MacTed> _blank2    a, b, c2
17:07:56 <MacTed> _blank2   a, b, c1
17:07:56 <MacTed> _blank1    a, b, c2
17:08:29 <dmcneil> cygri: oh, then i misunderstood the example
17:08:50 <dmcneil> ... still the case without a primary key, right?
17:09:11 <dmcneil> ... in this case it would have to be a stable blank node label across queries
17:09:26 <dmcneil> souri: inside the same translation, you may access the table twice, in two places
17:09:31 <dmcneil> ... the access order may be different
17:09:43 <dmcneil> ... based on that you may not be able to join the same rows
17:10:00 <dmcneil> ... so this even applies within the scope of the same query process
17:10:11 <dmcneil> macted: how is this relevant?
17:10:22 <dmcneil> souri: if we generate a blank node ID for a row
17:10:37 <dmcneil> ... then the same row from different parts of a query should generate the same blank node ID so they can be joined
17:13:31 <dmcneil> cygri: yes, that is what is required, and that is part of what it makes it so difficult
17:14:18 <dmcneil> macted: my model was that the blank node IDs are generated on the result set, not during the query
17:14:24 <Souri_> {?p :fname ?fnm} ... complex stuff ... {?p :lname ?lnm}
17:14:30 <dmcneil> ... this group is not about translating SPARQL to SQL
17:15:45 <dmcneil> cygri: the RDF concepts doc says "you don't know anything about blank nodes except whether they are the same"
17:16:00 <dmcneil> macted: but that applies to query results, not the underlying data
17:17:27 <Souri_> q+
17:18:33 <cygri> ericP: counter examples: jena, 4store, …
17:18:36 <MacTed> +1 ericP
17:18:49 <Ashok> ack next
17:18:58 <Ashok> ack next
17:19:51 <dmcneil> dmcneil: I think Richard's earlier statement that "doing nothing means DM and R2RML are completely separate" is quite overstated
17:20:12 <dmcneil> souri: I am still trying to understand the target for generating blank node IDs
17:20:26 <dmcneil> macted: for DM we need to maintain cardinality
17:20:35 <dmcneil> ... i.e. every row in the result set
17:20:56 <MacTed> q+ ericP
17:22:01 <Ashok> ack next
17:22:29 <dmcneil> eric: teh value of a bnode is not something that can be referenced later
17:22:33 <dmcneil> s/teh/the/
17:23:07 <dmcneil> ... the jena API over a SPARQL endpoint does not allow bnode IDs to be submitted again in subsequent queries
17:23:16 <Ashok> q?
17:23:23 <dmcneil> ... so it is ok that Jena over SQL does not provide persistent bnode IDs
17:23:34 <dmcneil> ashok: we are over time
17:23:40 <dmcneil> ... it is not clear how to make progress
17:24:33 <dmcneil> ... need either new proposals, or someone to change their position
17:24:47 <dmcneil> juan: can we summarize the current options and who supports them?
17:25:08 <dmcneil> ashok: if we only talk about changes to R2RML, then yes there are 3 options
17:25:13 <dmcneil> ... 1) do nothing
17:25:22 <dmcneil> ... 2) Richard's idea - add RowBlankNode
17:25:42 <dmcneil> ... 3) Souri's idea - add psuedo-column: "rowidentifier"
17:26:17 <dmcneil> .... 4) add wording saying "the DM is different in this special case"
17:26:48 <dmcneil> macted: I am less clear on these options than when we started
17:26:52 <cygri> 2) and 3) are variations of “fix R2RML”
17:26:59 <cygri> 4) is proposal A from last time
17:27:14 <cygri> 1) is B from last time
17:27:54 <Zakim> - +1.603.897.aaff
17:27:54 <dmcneil> macted: what happened to last week's proposal to strike the word "should"
17:27:59 <dmcneil> cygri: that is now option 4
17:28:44 <dmcneil> macted: i still like 4
17:28:48 <dmcneil> juan: me too
17:29:25 <MacTed> >>>  [[
17:29:25 <MacTed> >>>  If the table has no primary key, the row node is a blank node. Distinct blank nodes MUST be generated for rows with distinct column values. For duplicate rows with identical values, implementations SHOULD generate a fresh blank for each duplicate row (resulting in a non-lean RDF graph [RDF Semantics]). However, if the underlying database system does not provide any means to reliably differentiate among the rows, then
17:29:25 <MacTed>  implementations MAY re-use the same blank node for multiple duplicate rows (resulting in a lean RDF graph). Implementations SHOULD document and advertise their chosen behavior.
17:29:25 <MacTed> >>>  ]]
17:29:27 <MacTed> The above replaces the following sentence in the current DM spec --
17:29:30 <MacTed> >>>  [[
17:29:31 <MacTed> >>>  If the table has no primary key, the row node is a fresh blank node that is unique to this row.
17:29:33 <MacTed> >>>  ]]
17:31:02 <dmcneil> eric: I object to losing cardinality on the basis of something that R2RML cannot do
17:31:15 <dmcneil> ashok: would you be willing to word-smith it?
17:31:33 <dmcneil> eric: no, because I disagree with the premise of losing cardinality
17:32:07 <dmcneil> ... from the DMs perspective there is no reason the MUST should be relaxed to SHOULD
17:32:31 <cygri> i don't know how to handle it *with acceptable performance*, i should say
17:33:11 <dmcneil> eric: why are we breaking interop on the DM because R2RML cannot handle this case?
17:33:19 <dmcneil> +q
17:33:51 <juansequeda> q+
17:34:02 <Ashok> ack next
17:34:31 <dmcneil> dmcneil: but R2RML can handle it, use R2RML views
17:36:16 <cygri> q+
17:36:33 <cygri> q+ to answer: because the DM is the default mapping for R2RML
17:36:40 <dmcneil> eric: why don't we just tell R2RML users that they are losing cardinality in these cases?
17:37:15 <Ashok> q?
17:37:20 <Ashok> ack next
17:37:55 <dmcneil> eric: there is no issue in DM, the issue is an interop issue in R2RML
17:38:17 <dmcneil> cygri: I was working on the assumption that the DM is a default mapping for R2RML
17:38:32 <dmcneil> ... that should answer the question of why I expect the DM to accomodate the capabilities of R2RML
17:39:01 <dmcneil> ... if there are restrictions in R2RML, which is 1.0, then...
17:39:28 <dmcneil> eric: we have a case where R2RML cannot preserve cardinality
17:39:38 <dmcneil> ... we have a DM which provides default mapping for R2RML
17:40:03 <dmcneil> ... the places where R2RML cannot preserve cardinality, should be identified as the places where problems will occur
17:40:57 <dmcneil> cygri: R2RML as it stands, the user specifies the identities of the rows
17:41:02 <dmcneil> +1
17:41:12 <dmcneil> ... by specifying the columns or the templates
17:41:28 <dmcneil> ... if they lose cardinality they lose it because of how it was mapped, it is transparent
17:41:29 <dmcneil> +1
17:41:59 <dmcneil> ... the other point is: what do you suggest for me as an R2RML implementor
17:42:10 <dmcneil> ... push a button and get an automatic mapping
17:42:29 <dmcneil> ... what should that mapping be in the case of a table without primary keys
17:42:44 <dmcneil> eric: it should be what it is, just not promise to be the DM
17:42:55 <dmcneil> cygri: how to communicate to users that it is not the DM?
17:43:10 <dmcneil> eric: tell them R2RML does not have the ability to preserve cardinality in this case
17:43:24 <dmcneil> cygri: how should we describe the default mapping we implement?
17:43:40 <dmcneil> eric: say "it is similar to the DM except repeated rows will be collapsed into one"
17:43:49 <dmcneil> cygri: can we write that into the R2RML spec?
17:43:58 <dmcneil> eric: yes, that would be good
17:44:13 <dmcneil> cygri: so remove the R2RML reference from DM
17:44:22 <dmcneil> ... instead add a sentence to the R2RML spec
17:44:43 <dmcneil> ... saying the default mapping is the "DM - repeated rows"
17:45:08 <dmcneil> ashok: why remove R2RML ref from DM?
17:45:16 <cygri> The Direct Mapping is intended to provide a default behavior for http://www.w3.org/TR/2012/CR-r2rml-20120223/ [R2RML].
17:45:21 <dmcneil> cygri: there is a sentence in DM saying DM is default behavior for R2RML
17:45:25 <dmcneil> ... that sentence must go
17:45:33 <dmcneil> eric: we could add a caveat to it
17:45:56 <dmcneil> ashok: eric can you work with richard and david on this?
17:46:07 <dmcneil> eric: yes, i think the wording is close to what ivan proposed
17:46:27 <dmcneil> cygri: it would also have to address the repeated rows caveat
17:47:19 <dmcneil> seems to be concensus that we will try to develop wording around this
17:47:40 <dmcneil> ashok: we will try to work it out in email
17:47:44 <dmcneil> thanks :)
17:48:18 <Zakim> -cygri
17:48:20 <Zakim> -dmcneil
17:48:20 <Zakim> - +1.603.897.aaee
17:48:21 <Zakim> -EricP
17:48:21 <Zakim> -Ashok_Malhotra
17:48:23 <Zakim> -MacTed
17:48:28 <Zakim> -juansequeda
17:48:29 <Zakim> SW_RDB2RDF()12:00PM has ended
17:48:29 <Zakim> Attendees were +1.781.273.aaaa, MacTed, Ashok_Malhotra, +1.314.395.aabb, +3539149aacc, cygri, +575737aadd, juansequeda, nunolopes, dmcneil, +1.603.897.aaee, +1.603.897.aaff, EricP
17:48:37 <Ashok> rrsagent, make logs public
17:48:50 <Ashok> rrsagent, make minutes
17:48:50 <RRSAgent> I have made the request to generate http://www.w3.org/2012/05/15-RDB2RDF-minutes.html Ashok