Re: A Direct Mapping of Relational Data to RDF is FPWD

Re modeling any vendor's type, I think if your intention is to map real data in 
real systems, then yes you should at least leave that part of the spec open 
enough that it can be done and you should lend direction where it's useful.  

6) I think you're missing my point that this is a great opportunity to give a 
(non-normative) example of R2RML and tie the two together.





________________________________
From: Alexandre Bertails <bertails@w3.org>
To: Alex Miller <alexdmiller@yahoo.com>
Cc: Eric Prud'hommeaux <eric@w3.org>; Michael Hausenblas 
<michael.hausenblas@deri.org>; RDB2RDF WG <public-rdb2rdf-wg@w3.org>
Sent: Thu, November 18, 2010 3:06:56 PM
Subject: Re: A Direct Mapping of Relational Data to RDF is FPWD



On Thu, 2010-11-18 at 11:53 -0800, Alex Miller wrote:
> My first reaction was that it might be a bit over-rigorous in this
> case:

First, thanks for the feedback.

I'll answer more specifically on the formalism, letting Eric answering
about the more Semantic Web oriented questions.

> sealed abstract class SQLDatatype
>   case class SQLInt () extends SQLDatatype
>   case class SQLFloat () extends SQLDatatype
>   … 
> case class SQLString () extends SQLDatatype
>  
> Using a sealed class here says that this is the complete set of
> possible data types.

We just find easier to rely on exhaustive pattern matching during spec
development. It's an implementation detail.

> That seems like painting yourself in a pretty small box when it comes
> to the richness of data types found in dbs in practice.

The real question is: do we want to model *any* vendor's type? Or only
the ones from the SQL specification?

And don't worry, this is a First Public Working Draft. Things can change
a lot before it becomes a Recommendation. By giving your feedback (and
participating to the Working Group), you have an opportunity to
influence our work.

> FYI, Revelytix is actually using Clojure for our implementation
> (although we considered Scala closely too).  

Nice! It will also be easy for you to implement the Direct Mapping, or
just works on ours :-)


> Some other comments:
> 
> 
> 1) I saw the requests for explanation of the #_ row IRIs on the list
> but I don't recall ever seeing the answer.  Easily could have been in
> the minutes that I didn't read though. :)   I saw the hash-vs-slash
> note in the spec but is the trailing _ just to have something after
> the #?
> 
> 
> 2) I was surprised at a first glance to see ,'s in the compound key
> IRIs but it's equivalent to the same information we're using in our
> subject IRIs.  
> 
> 
> 3) We were not smart enough to use blank nodes for tables w/o primary
> keys and just punted on the issue but I think the blank node solution
> works well.
> 
> 
> 4) We went back and forth on what to do when having multiple unique
> keys in a table and whether to create multiple "same as" identifiers
> in that case to the primary key subject IRI.  You're consistently
> using the PK subject IRI which I think is the right choice for the
> direct mapping.  I haven't looked at R2RML enough yet to understand
> the range of choices there.
> 
> 
> 5) Issue (formalism-model) refers to sections 5 and 6 but those should
> be 3 and 4.  Personally, I find the definition to be easier to read
> than the rules, but that's probably due to familiarity. 

Some last minute edit made the reference inconsistent. The W3C Webmaster
has already been slapped for inattentiveness.

> 6) It would be really nice to see an equivalent R2RML that produces
> the direct mapping.

Actually, one of the applications of the Direct Mapping is to serve as a
default mapping for R2RML, when you give an empty configuration.

Alexandre.

> 
> 
> ______________________________________________________________________
> From: Alexandre Bertails <bertails@w3.org>
> To: Eric Prud'hommeaux <eric@w3.org>
> Cc: Alex Miller <alexdmiller@yahoo.com>; Michael Hausenblas
> <michael.hausenblas@deri.org>; RDB2RDF WG <public-rdb2rdf-wg@w3.org>
> Sent: Thu, November 18, 2010 12:53:14 PM
> Subject: Re: A Direct Mapping of Relational Data to RDF is FPWD
> 
> On Thu, 2010-11-18 at 12:43 -0500, Eric Prud'hommeaux wrote:
> > * Alex Miller <alexdmiller@yahoo.com> [2010-11-18 08:26-0800]
> > > Looks great all.  I've just skimmed through it but it's
> interesting seeing how 
> > > you've handled certain issues in similar and different ways from
> what we've done 
> > > at Revelytix. 
> > > 
> > > We are interested in supporting these specs moving forward
> although I'm not sure 
> > > yet when we'll start working on it.  If things move along
> favorably we may also 
> > > be able to open source the implementation at some point.
> > > 
> > > I was surprised (and delighted) to see the Scala syntax in the
> spec too. :)  
> > 
> > It's perhaps over-rigorous for the purposes of presentation (uses
> case
> > classes rather than type= to ensure type safety). The source:
> >
>https://dvcs.w3.org/hg/FeDeRate/file/tip/directmapping/src/main/scala/DirectMapping.scala
>a
> 
> Case classes are the Scala algebraic datatype implementation. They
> define both types (the classes) and type injectors (the constructors).
> 
> Sure, we should split the formal definition from the type-safety
> proof.
> 
> Pattern matching + type-checking is not "over-rigorous" when you gain
> such confidence in your formalism.
> 
> Alexandre.
> 
> > 
> > is editable by RDB2RDF members.
> > 
> > > ________________________________
> > > From: Michael Hausenblas <michael.hausenblas@deri.org>
> > > To: RDB2RDF WG <public-rdb2rdf-wg@w3.org>
> > > Sent: Thu, November 18, 2010 10:06:29 AM
> > > Subject: A Direct Mapping of Relational Data to RDF is FPWD
> > > 
> > > 
> > > All,
> > > 
> > > Congrats to the team, esp. a big thanks to the editors - "A Direct
> Mapping
> > > of Relational Data to RDF" [1] is now published as FPWD.
> > > 
> > > Cheers,
> > >      Michael
> > > 
> > > [1] http://www.w3.org/TR/rdb-direct-mapping/
> > > 
> > > -- 
> > > Dr. Michael Hausenblas, Research Fellow
> > > LiDRC - Linked Data Research Centre
> > > DERI - Digital Enterprise Research Institute
> > > NUIG - National University of Ireland, Galway
> > > Ireland, Europe
> > > Tel. +353 91 495730
> > > http://linkeddata.deri.ie/
> > > http://sw-app.org/about.html
> > 
> 
> 
> 
> 

Received on Thursday, 18 November 2010 21:43:13 UTC