See also: IRC log
<trackbot> Date: 17 May 2011
<ericP> network is back
<ericP> ahh good, everyone is happy
<MacTed> someone was asking about R2RML implementation timing in a recent call.... can add a first-cut for Virtuoso to that list, now anticipated for June if not sooner
i can scribe
<mhausenblas> scribenick: dmcneil
thanks: )
<mhausenblas> PROPOSAL: Accept the minutes of last meeting http://www.w3.org/2011/05/10-rdb2rdf-minutes.html
RESOLUTION: minutes accepted by working group
last call planning...
<mhausenblas> http://www.w3.org/2001/sw/rdb2rdf/wiki/Main_Page#Countdown_to_Proposed_Recommendation
<mhausenblas> ACTION-125?
<trackbot> ACTION-125 -- Ashok Malhotra to draft Wiki page with LC sprint time line with Sep 2011 LC -- due 2011-05-17 -- OPEN
<trackbot> http://www.w3.org/2001/sw/rdb2rdf/track/actions/125
<mhausenblas> close ACTION-125
<trackbot> ACTION-125 Draft Wiki page with LC sprint time line with Sep 2011 LC closed
michael: do the editors agree with the timeline?
souri: need to think about how many issues, and how many "sticky" issues
ashok: we can close it, so we don't take any until last call
there are 9 open issues, none look very difficult
michael: there are more than just open issues, last time we reviewed them and concluded we needed to resolve a couple per call
what does it mean to "close it", working group members are encouraged to raise issues
ashok: meant to close current issues then not accept more until after last call is published
michael: maybe we could call it "freezing" the list
cygri: we know there are issues to be resolved and a timeframe to do it in, as long as we make progress and knock off issues each week then we are on track
so we should focus on closing issues
juan: so by Sept 1 all issues need to be closed?
ashok: yes, either closed or postponed
juan: so after last call we can still close issues
ashok: are there any open issues on Direct Mapping?
juan: yes
<Zakim> mhausenblas, you wanted to state it is not about the current issues
michael: the issue with freezing the list is not about current issues but new issues
cygri: i think if we freeze the queue now then we prevent ourselves from hearing about issues
implementors will find issues or ask for clarification, we need to hear about these
<Seema> +1 to Richard's comment
if we really run out of time then we acknowledge hearing the feedback but delay addressing it until after last call
maybe will need to freeze later
ted: agrees with Richard
michael: do we need a resolution for this?
ashok: no
michael: on to action items
<mhausenblas> ACTION-127?
<trackbot> ACTION-127 -- Richard Cyganiak to write up a proposal to resolve ISSUE-32 based on today's discussion -- due 2011-05-17 -- OPEN
<trackbot> http://www.w3.org/2001/sw/rdb2rdf/track/actions/127
<mhausenblas> close ACTION-127
<trackbot> ACTION-127 Write up a proposal to resolve ISSUE-32 based on today's discussion closed
<cygri> http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2011May/0029.html
<cygri> thread starts here ^
<cygri> david's version: http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2011May/0030.html
<cygri> another proposal from me: http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2011May/0035.html
<Souri> "col1=>col2"
<cygri> rr:joinCondition [ rr:child "col1"; rr:parent "col1" ];
souri: was thinking that David's proposal isolates each column in a separate property, which makes it easier to deal with special characters in the column names
e.g. if a column was named "foo=>"
cygri: agrees that approach is clearly modelled and avoids certain syntax issues
escaping comment intersects with another thread of discussion regarding special characters
beleives that "=>" is not valid in un-quoted SQL identifiers
<Souri> Oracle: create table "a=>b" (a int);
<cygri> SELECT "foo=>" FROM table;
this means that we would have to quote the column name again anyway
<cygri> rr:column "\"foo=>\""
"\"foo\""
<cygri> rr:joinCondition "\"col1=>\"=>col2"
so the handling of special characters is not a distinguishing characteristic of the alternatives
cygri: although it is very verbose, if there is group agreement then we can go that way
souri: appreciates the clarity of the more verbose approach
<cygri> PROPOSAL: resolve ISSUE-32 as per http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2011May/0030.html
<Souri> +1
<cygri> ±0
michael: any objections?
<MacTed> +1
RESOLUTION: working group resolves ISSUE-32 as per http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2011May/0030.html
michael: now we need an action to write this in the editors draft
cygri: i can do it
<mhausenblas> ACTION: Richard to implement ISSUE-32 as resolved today (based on http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2011May/0030.html) [recorded in http://www.w3.org/2011/05/17-rdb2rdf-minutes.html#action01]
<trackbot> Created ACTION-130 - Implement ISSUE-32 as resolved today (based on http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2011May/0030.html) [on Richard Cyganiak - due 2011-05-24].
<mhausenblas> ACTION-129?
<trackbot> ACTION-129 -- Ashok Malhotra to check re DB2 and SQL-Server for ISSUE-35 (case sensitivity of SQL identifiers) -- due 2011-05-24 -- OPEN
<trackbot> http://www.w3.org/2001/sw/rdb2rdf/track/actions/129
<mhausenblas> close ACTION-129
<trackbot> ACTION-129 Check re DB2 and SQL-Server for ISSUE-35 (case sensitivity of SQL identifiers) closed
ashok: almost all databases follow the SQL standard: column names and table names are case insensitive except when double quoted
in which case they are handled in a case sensitive manner
SQL Server is the only one that is different, you can configure it to behave differently than the standard
so we probably need to say that you should follow the guidelines of your database
souri: does the SQL standard allow double quotes in the identifiers?
oracle allows everything else (as long as it is quoted) except double quotes
<mhausenblas> ACTION-126?
<trackbot> ACTION-126 -- Souripriya Das to implement ISSUE-18 resolution and make sure that all class and property names are meaningful -- due 2011-05-24 -- OPEN
<trackbot> http://www.w3.org/2001/sw/rdb2rdf/track/actions/126
souri: not done yet, discussion was about having "Class" as a suffix on the class names in the R2RML spec
to avoid naming conflicts with the property names
so they do no just differ by the case of the first character
so we can keep "Class" at the end of the class names
cygri: we can avoid similar names with ad-hoc tweaking of one of the terms
using slightly different wording
<Souri> example: class => rr:SubjectMapClass and property => rr:subjectMap
there are examples from other ontologies where they differ only in the case, so while it is not good, we would not be the first spec to do this
<mhausenblas> Michael: how about rr:SubjectMap and rr:mapsTo
<MacTed> or mapsSubject or ...
<Seema> similar names for class and property are confusing..not particularly thrilled with that approach
ted: agrees with using different terms (it is madness to have just case differences)
<mhausenblas> ACTION-128?
<trackbot> ACTION-128 -- Michael Hausenblas to find the resolution re what SQL and SPARQL we address and make this explicit core requirements in the UCR document -- due 2011-05-31 -- OPEN
<trackbot> http://www.w3.org/2001/sw/rdb2rdf/track/actions/128
+q
:)
souri: could make properties verbs
will keep the request for clarity in mind as new proposed names are assembled
moving on to issues
<mhausenblas> ISSUE-41?
<trackbot> ISSUE-41 -- Define how rr:column, rr:template, etc. handle NULL column values -- raised
<trackbot> http://www.w3.org/2001/sw/rdb2rdf/track/issues/41
<cygri> http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2011May/0042.html
on ISSUE-41 there were several +1 votes for not producing triples if a column was null
on the mailing list
+q
<Seema> +1 for option 2
souri: ok with that option, but there is another option where we could produce a NULL literal
<soeren> +1 for option 2
<privera> +1 for option 2
ashok: what would a NULL literal mean in RDF?
<MacTed> -1 option 2
dmcneil: a couple of clarifications: so a template with many columns, any of them being null means that the triple would be produced?
if users need to map NULL db values to default values then they would need to do it in a SQL query?
<Souri> <John> :hasAge "" .
ted: NULL values can have meaning in the relational world
cygri: blank nodes correspond to unknown values
ted: no, blank nodes are for unnamed values
<Ashok> XML Schema has a concept called NIL which corresponds to the SQL NULL
cygri: a blank node is an existential value that says something exists, but nothing more about it
<Souri> bNode => existential, <John> :hasAge _:b1 .
discussion degrades
souri: blank node allows a value to be identified without providing other details (e.g. if that blank node never appears again in the graph)
ted: NULL values may have meaning in a relational schema
+q
ashok: that requires us to create a special "value" to correspond to NULL
that means we are adding to RDF
ted: no, just adding to R2RML and Direct Mapping
<MacTed> :cell :prop "DB_NULL"
dmcneil: users could define their schema specific expectations for NULL in a SQL query
<Souri> SQL => select y from tab WHERE x IS NULL
ted: that requires users to have too sophisticated of a model
<Ashok> <John> :hasAge UNDEFINED
<MacTed> ?s ?p "NULL"
<MacTed> ?s ?p UNDEFINED
juan: so the output should include the NULLs?
<juansequeda> person(name, age)
<juansequeda> person(Juan, NULL)
<juansequeda> :id1 <name> "Juan".
<juansequeda> :id1 <age> NULL ==> is this what you want?
<MacTed> :id1 <child> "Bob"
<MacTed> :id2 <child> NULL
<Souri> Should we support an option for a TriplesMap: 1) NULL => disappears 2) NULL => translated to "" (a simple literal) [is ""^^xsd:integer legal in RDF?]
cygri: in Direct Mapping I think it might make sense to preserve the NULLs
but in R2RML a query can be used to handle NULLs
michael: out of time
cygri: maybe ted can write a counter-proposal
souri: how to treat a NULL in a table may vary from table to table
from that point of view, we could always create a view in R2RML
but that is a longer way of doing things
so what if R2RML included a property defining what value to produce for NULL
this can vary between triplesmaps
?: but what about Direct Mapping
<juansequeda> that is Marcelo
ted: yes, I think so
document the default, and provide an easy way to change it
ashok: but on Direct Mapping we have said there are no switches, just one algorithm
ted: then it must preserve nulls
souri: given the RDF I should be able to reconstruct the table
so the Direct Mapping by default (and since there are no switches) so it must preserve the NULLs
cygri: then the way to go is a blank node
there is something there but we don't know what it is
soeren: NULL in the db says there is nothing there
ashok: it is the lack of a value
<Souri> Is ""^^xsd:integer a valid RDF value?
soeren: consider an integer column: 0 is different than NULL
so creating no triple for this makes sense
ted: but it is schema dependent
cygri: in SQL, NULL is a special thing, it is not simply "there is no value", it can be used in different ways
sometimes it is used to indicate "there is a value, but we don't know it"
soeren: then we could say that sometimes NULL means 100
most common interpretation is "there is no value"
despite the fact that it can be abused
ted: the most common understanding is to abuse it
soeren: then ignore it because it is nonsense
cygri: agree that R2RML should ignore it, because you can customize it
souri: should be able to look at output triples to conclude that we have a column in the the table (when that column only has NULL values)
(talking about Direct Mapping)
michael: can we have a proposal for ISSUE-41?
ISSUE-41 is for R2RML actually, right?
i think the counter-proposal is to default it to suppress, but add a property to specify what vbalue to use for null
on a per triplesmap basis
michael: we can write to Pat (?)
souri: how do we know the type of the column if there are only NULL values?
cygri: also consider empty tables
must look at schema to preserve schema information (looking at data does not work)
question for Pat: is a blank node an accurate representation of a NULL value from a relational database?
<mhausenblas> ACTION: Hausenblas to write mail to Pat regarding ISSUE-41 - is a blank node an accurate representation of a NULL value from a relational database? [recorded in http://www.w3.org/2011/05/17-rdb2rdf-minutes.html#action02]
<trackbot> Created ACTION-131 - Write mail to Pat regarding ISSUE-41 - is a blank node an accurate representation of a NULL value from a relational database? [on Michael Hausenblas - due 2011-05-24].
<mhausenblas> [meeting adjourned]
<mhausenblas> trackbot, end telecon
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