Re: To embed or combine

On 11 Sep 2007, at 10:24, Dave Reynolds wrote:

> Jos de Bruijn wrote:
[snip]
>> Thinking about it a bit more, I actually do not think a built-in like
>> isBlanknode could be defined in a meaningful way while observing the
>> semantics of blank nodes.
>
> See SPARQL.

It's questionable whether the currently specified SPARQL query  
language observes the *semantics* of blank nodes. I certainly  
questioned it :) Current SPARQL queries are best understood, IMHO, as  
queries on the explicit term structure of the RDF Dataset.

> The ability to detect blank nodes as part of a condition language  
> is as useful in the RIF condition language as it was in the SPARQL  
> query language - there is little difference between the condition  
> part of a horn rule and query. I'm trying to ensure we are  
> compatible with the existing standards here
[snip]

The standards are somewhat in conflict, or so I have argued. They can  
sort of not be in conflict by arguing that a term structure query  
language is a useful thing and there is a standard for the term  
structure. They may in fact not be in conflict is someone can come up  
with a story that plausible makes everything align (which we tried  
and didn't succeed at in the DAWG). Plus, things may be somewhat  
underspecified.

Finally, I think it's more important to be compatible with dominant  
practice than with the literal text of the spec. Specs can get things  
wrong, after all, and are not holy writ. SPARQL certainly does that  
for RDF query.

So, it would be wise to separate out two things: whether something  
like "isBlankNode" a la SPARQL is worth supporting (I think yes) and  
whether aligning with bnode semantics (i.e., as undestood as graph  
scoped existential variables) is worth supporting (and what, exactly,  
that support means! which is part of the rub).

Cheers,
Bijan.

Received on Tuesday, 11 September 2007 09:48:21 UTC