See also: IRC log
<trackbot> Date: 31 August 2010
<mhausenblas> scribenick: boris
<mhausenblas> http://lists.w3.org/Archives/Public/public-rdb2rdf-wg/2010Aug/0060.html
<mhausenblas> PROPOSAL: Accept the minutes of last meeting, see
<mhausenblas> http://www.w3.org/2010/08/24-rdb2rdf-minutes.html
+1
<juansequeda> +1
RESOLUTION: last minutes approved
souri: dont have comments
rgarding lookup table
... richad is not here ... so ...
... To find actual use case for this lookup table
... let's discuss this next week when richard will be here
Michael: ok
michael: we need to create test
cases ....
... boris volunteer to take care of this subject
<mhausenblas> http://www.w3.org/2001/sw/rdb2rdf/wiki/R2RML_Test_Cases
michael: brief introduction for the test cases
<mhausenblas> http://www.w3.org/2001/sw/rdb2rdf/test-cases/
michael: currently the docs are
as pdf
... we have came for the test cases
... input sql, and the mapping file and the expect output
... the sparql query will check if the resultant rdf is
oik
... questions?
someone: .... all the triples in
the sparql query?
... no additonal triples
soeren: it is not testing for conformance
<juansequeda> +q to ask what are we testing. Is it correctness and/or performance ?
souren: test the triples not the superset
michael: no test case for
performance
....: two fold
...: check the semantics we describe in the R2RML doc is what
we mean
....: during the phase of the development of the R2RML DOC
<hhalpin> correctness
testing
...: next phase will be to test implementarions
juan: we will give manually the input and the output
<Souri> SPARQL working group has good and tested scheme for test specifications
michael: yes...
... it is useful have sparql query rather than the rdf triples,
... but we are open to discuss
<juansequeda> souri, can you
send out the link to the sparql group's test cases
...: we can have additonal triples, provenance for exmaple
....
....: that's why is good to have the sparql queries
<Zakim> juansequeda, you wanted to ask what are we testing. Is it correctness and/or performance ?
<Zakim> ericP, you wanted to second soundness
<hhalpin> soundness would be a subset of correctness testing
eric: we have bunch of
implementations with more liberal equality testing ...
....: we have at least it is true, ... we couldn't tell there
are some erronous values
... we can have some "extened" mode
...: for the implementaros
....: completeness ericP
michael: we are open to discuss
more on this ...
...: if you think this is more sense is ok,
soeren: it is very important, it
is really importanto to check no additional thing is
included
... maybe add another sparql queries included the numbrers of
triples
michael: it will take some time to set up completely ...
<ericP> <sparql><boolean>true</boolean>
michael: we are going to work on test cases, and we once we will have sth there ....
juan: one example database?
michael: one example database per test case rathern than one big database
juan: we can have non-normalized database
michael: think in very simple
test cases ... later on we can have more complex test
cases
... in the beginning only simple test cases
juan: test cases for RDF, or SPARQL?
michael: yes, they are similiar,
....
... questions ...? ...
eric: status?
... Richard and Eric, write some use cases, originally for
simple scenarios
... single tables with primary key
<mhausenblas> ACTION: Michael to send sample TC to the group [recorded in http://www.w3.org/2010/08/31-rdb2rdf-minutes.html#action01]
<trackbot> Created ACTION-71 - Send sample TC to the group [on Michael Hausenblas - due 2010-09-07].
eric: rewrote the notion of you have relations with or not primary key, not always composed, and FK not composed
<hhalpin> note that I'm happy to help set up test-cases for you boris.
eric: there is an example of that on the document
<ericP> http://www.w3.org/2001/sw/rdb2rdf/directGraph/
<hhalpin> i.e. in W3C CVS etc.
<hhalpin> I'm happy to take that as an action.
<ericP> http://www.w3.org/2001/sw/rdb2rdf/directGraph/#multi-key
eric: multi-key example
juan: multiatrtibute key?
eric: is describing the table
...
... hardest cases in Relational model ... bunch of set
defintions on the section 5 ....
....: relation definitions 4.1 to 4.2 ...
juan: discuss with marcelo about,
work together on this .... from the DB perspective ... it's a
kind of BNF rule ...
... this is not the way you define a relational model
... suggest to put this in datalog?
... no use this BNF style
....: don't see anything to coming out, this is just bunch of
rules
cygri: doesn't agree to use the definition from the DB ?
<juansequeda> http://www.w3.org/2001/sw/rdb2rdf/wiki/Semantics_of_R2RML
juan: the semantics of datalog
....
... ... every predicate is a relation ... right there
... well defined semantics
....: eric just have BNF rules and type of injectors
cygri: understandability more important to be formal
<juansequeda> http://www.w3.org/2001/sw/rdb2rdf/wiki/Default_Mapping
<soeren> +q
cygri: insits to check how the "text books" introduce relational model
juan: link to the wiki, we have on datalog is much understable that the thing from eric
cygri: not talking as eric
proposal
...: just check text books
dan: check the books and chapters of datalogs
soeren: relational algebra
introduces the semantics of relational db
...: datalog will introduce things more complicated
....: let's focus only the relational algebra
dan: let's look at the dabases
... datalog = realtiona algebra
... a lot of people will find more confortable ... encourage
people to check relations books
... what is commonly done
juan: sparql is datalog and datalog = relational algebra
<Zakim> ericP, you wanted to say that soeren's proposal would work for the doc which translates queries
eric: there is no notion of join
(forexmaple)
....: relational algegra .... (joins, etc) ... not use in ...
RDF
juan: only selection and projection ....
eric: datalog is horn- functions ... two issues
<juansequeda> DATALOG: course(id, name) = SQL: select id, name from course
eric: 1. I will need prolog to the some operations
dan: commonly accepted to add this in datalog
juan: the semantics of this mapping language is based in datalog ...
eric: is it prolog?
dan: yes, datalog is a subset of prolog
<Zakim> mhausenblas, you wanted to ask who the intended audience of this document is
michael: who is the intented audience will be? who is supposed to read this? ... and the we can follow some direction
eric: d2r folks
michael: people who write the engine
?
eric: write the engine implemetatnoins
juan: not only d2r, oracle, ibm
micahel: people who write the engine ... is the primary audience
eric: machine exectubale
transforamtion written in prolog? ... another issue is the set
semantics .... in some cases you use cardinality
... add aggregates it costs ..... how we presevered
cardinalidty, set of sematnics
when sql standaraziton process ... there wont be agregates? .... cardinality was expense?
souri: practical to allow
duplicates ...
... supose someone define a mapping ... do not have a primary
key ... two rows the same URI ... unless we use distintict we
will have duplicates
... try to supress duplicates ... not easy
<mhausenblas> s/soeren: supose/souri: suppose
eric: if there is no PK, expressing attributes in a tuple, ... blank node
souri: define a mapping, Uri corresponds a row ... every instance ....
eric: project the uniqueness
...
... not necessary ...
....: example of tweets .... not identifiers for the tweets¿
... example on section 2.2
...: non-existing PK
....: preserves cardinality ...
souri: basically again, best
practice from his point view ....
... implementation of bad cases ....
michael: we have one concrete proposal from eric ... and default mapping by Juan is an alternative proposal
juan: again everything in datalog
eric: is prolog
juan: if we present the tihngs to ibm, is not going to be easy
soeren: oracle doc. there are a
lot of datalog?
... first relational algebra ... his impresion ...
... or I am wrong?
souri: more sql, more practical
people
... there are some things in relational algebra
... practitioners use tables, cols, not theory
<mhausenblas> http://www.w3.org/2001/sw/rdb2rdf/directGraph/
<hhalpin> +1 souri, and let's see what subset of it we can grab in Datalog/RIF.
michael: it will be good if you take the eric's job and rewrite into datalog?
juan: Marcelo and I did it already
souri: is like a rule ... what we that expect
juan: is a rule ... default
mapping should have semantics
... BNF and the semantics are in datalog ... that is his
concern
michael: we can expect sth next week?
juan: ok
<Zakim> ericP, you wanted to ask if we can talk about prolog instead of datalog
ericP: prolog?
juan: datalog + built-in function, not prolog
<mhausenblas> how about prolog--
<mhausenblas> :)
ericP: is in between ... ok
juan: semantics of the language are eq to datalog
cygri: there are different ways
to define the semantics of the language
...: of course the semantics have to be written
<hhalpin> cygri - basically *any* mathematical structure can serve as semantics
<hhalpin> and we do not *have* to write them in my opinion.
<hhalpin> But often it does help us think through what's going on in the spec.
cygri: db community is not
datalog ...
... another arguments?
<hhalpin> Generally, I think we should do the semantics in a way that ideally would help a programmer understand what's going on.
dan: important who the audience
is for the document?
... implementors of the engine
<hhalpin> Datalog, being so close to FOL, is some thing quite a few people understand.
<hhalpin> but we need to be
clear the semantics are also subservient to the users.
...: different database implementors types
<hhalpin> i.e. ashoks' point was correct
<hhalpin> that we don't want to restrict users
juan: reason why to datalog is because SPARQL=SQL via datalog
<hhalpin> or make them learn a whole new language..
juan: sematnics of the language = datalog ... here are the semantics
<hhalpin> my suggestion would be to go forward with merging eric's work and writing down souri's using a syntax
<hhalpin> and *then* work on the semantics on the side.
juan: we should learn from the issues about the semantics
cygri: we can write the semantics in different languages
<hhalpin> and the semantics might help us catch a bug.
<hhalpin> they tend to...
dan: including english, NL ...example
michael: juan means formal semantics = semanticas
<hhalpin> however, we do not want semantics to be a rathole, we need to get a FPWD out asap.
<ericP> 1+
soeren: formal semantics are very important .... translating SPARQL algebra into relational algebra ... it will be clear ...
<soeren> http://www.informatik.uni-leipzig.de/~auer/rdb2rdf/semantics.pdf
juan: he has to look at that ... sparql to sql translate
<hhalpin> let's get FPWD with syntax based on a combo of Souri's proposal and ericP's proposal out there.
<juansequeda> Semantics preserving SPARQL-to-SQL translation -> http://www.cs.wayne.edu/~shiyong/papers/dke09_artem.pdf
ericP: continue on the direct
mapping ....
... RDB here is the RDF graph ... SPARQL query here is the
underilyng relational algebra
... first option
michael: neext week about the
syntax
... and the semantics, and juan let us know if he is ready or
not
<mhausenblas> thanks for joining in cygri
<mhausenblas> best wishes to all at I-Semantics, cygri
<ericP> ditto
<mhausenblas> [adjourned]