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
> 
> 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 21:07:09 UTC