Re: On semantics-based approaches and still using full vendor-specific SQL


I think your summary is spot-on.

Thank you very much for taking the time with the Edinburgh database  
Per an earlier email of mine, one hour teleconferences is a very  
challenging way
to transmit all the necessary explanations.



On Jul 23, 2010, at 1:23 PM, Harry Halpin wrote:

> I spent most the day with the Database Research Group here at  
> Edinburgh,
> who kindly managed to read most of the proposals on the table. So, I'm
> going to try to channel the results of the discussion to the group.
> One way is to use a purely SQL-based approach (which I hope Souri  
> will be
> present the week after this one) that allows the mapping to be done  
> as a
> view (that is isomorphic to the triples) using the full  
> expressivity of
> SQL. Then a very simple mapping construct can map the results of  
> this SQL
> to a graph, i.e. by generating URIs.
> Another way is a purely SQL-based approach, but then expect the  
> mapping
> language to provide a few easy-to-use  basic constructs besides just
> generating URIs in order to do common tasks, i.e. create new nodes  
> etc. I
> think this is the approach that Marcelo and Juan have been  
> advocating for.
> Now, I think these two approaches are compatible, as long as the few
> easy-to-use basic constructs can be limited to a sensible amount  
> that can
> be translated into SQL and they do *not* preclude using full-vendor
> specific SQL to create the mapping as well, i.e. in a view.  This  
> makes
> sense, as SQL itself can be viewed using Datalog semantics.
> Furthermore, people that are SQL wizarde, these basic constructs may
> not be necessary, but some people may find them (particularly  
> people from
> an RDF background) easier to use than doing everything in pure SQL.  
> So,
> Marcelo and Juan's approach this does not necessarily limit the
> expressivity of SQL as long as it does preclude creating a view  
> using full
> vendor-specific SQL  before some basic mapping functions are called.
> Lastly, the differences between Eric's RIF-based approach and the  
> Datalog
> approach are negligible in practice, as RIF is essentially also  
> based on
> Datalog semantics, i.e. RIF *is*  a syntax for Datalog (which does not
> have its own syntax) plus some bells and whistles for  
> extensibility.  The
> argument between using Datalog or a set-theoretic semantics for  
> mapping is
> not necessary, as Datalog also has a standard set-theoretic semantics
> (although we do need to get the exact semantics of what we mean by
> "Datalog" down).Soeren's approach of mapping SPARQL to SQL is also  
> useful,
> and should be used as a test if there is enough time, as it still  
> depends
> on the first possibly non-trivial mapping of relational data to RDF  
> to be
> done (likely non-materialized).
> Would like to hear opinions - just trying to build consensus in the  
> group,
> which despite surface differences, is actually becoming closer I  
> think.
>         cheers,
>              harry

Received on Friday, 23 July 2010 19:16:47 UTC