Re: Using Datalog as a common semantics for SQL/RIF-based approaches?

Harry


On Sun, Jul 18, 2010 at 10:39 AM, Harry Halpin <hhalpin@w3.org> wrote:

> In our specification, it will be important to both specify exactly what
> needs to be implemented that users can expect to be portable and have
> extensibility mechanisms that work in a principled manner.
>
> The options that we've seen so far both seem to have problems. SPARQL
> constructs are not expressive enough, but then RIF is likely too
> expressive, and it would be doubtful if we could convince implementers to
> implement all of RIF just to map relational data to RDF. Likewise, SQL is
> a large language itself that is implemented differently in the details
> across vendors, so we'd have to specify exactly what part of SQL we
> thought must be implemented. How to do so?
>
> I'm intrigued that we could use another option - specify a common
> semantics using Datalog that then could be expressed using some subset of
> RIF and SQL. In fact, ideally the language could use Datalog to translate
> between the subset of RIF and SQL and vice-versa. Then we could also take
> advantage of SQL's power and implementation exprience while having the
> nice extensibility mechanisms of RIF.
>

Yes!!

+1

>
> However, I'd like to know exactly what part of RIF-BLD covers Datalog, and
> what exact fragment of SQL maps to Datalog. Examples of mappings are not
> enough, we'd have to specify  the kinds of RIF/SQL expressions that would
> be allowed and how both expressions mapped to Datalog.
>

I think the datalog to RIF question is for Harold Boley.


In [1] it states: SPARQL can be partially mapped to Datalog (and thus to the
RIF-Core subset of RIF-BLD)
Does that mean that it is all of RIF-BLD? Maybe we should has Harold Boley.

And about datalog to SQL, if I'm not wrong (marcelo and dan, please correct
me) the correspondence are just SELECT-FROM-WHERE without aggregation and
grouping... basically the core relational algebra (selection and
projection). If i'm not wrong, then that means that this corresponds to Horn
clauses without recursion and negation.

[1] http://www.w3.org/TR/rif-bld/


>        cheers,
>              harry
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