Re: spruced up definitions

On May 24, 2005, at 11:07 AM, Pat Hayes wrote:

>> Thanks for the comments and rewokred definitions.
>>
>> I'll process them, send you an updated set of definitions as well as 
>> send any
>> questions I have.
>>
>> One question for now - if we go with "subgraph", is there any reason 
>> why the
>> predicate should not be a blank node?
>
> In the pattern, you mean? I guess not, though if we allow this then we 
> might want to draw reader attention to the non-RDF-ish nature of those 
> patterns,

They are already a bit non-RDF-ish (literals in subject positions), but 
further highlighting is always good. (Pink highlighting, preferably.)

> and that they amount to asking "does a predicate exist such that...".

Well, if you interpret them that way :) I presume you don't intend to 
interpret that  second orderly. As I've said, I've a bit of pechant for 
interpreting them metalinguistically.

>  That is, any answer binding must instantiate the bnode to a URIref. 
> Or, of course, we could just prohibit them :-)
>
> BTW, I don't see that this is affected by the subgraph/entailment 
> decision. Am I missing something?

If we allow bnodes in predicate positions, and want to use the "natural 
data" entailment to define queries (i.e., a query is true of a kb just 
in case the kb entails the query, where the entailment function depends 
on the expressiviity of the KB. So, if the kb is RDF, query success is 
defined in terms of rdf entailment. But then no query pattern with 
bnodes in predicate positions will hit (at least, not without some 
extension).

hence my preference for treating predicate query variables as 
metalinguistic. Then such queries are actually query schemas which get 
expanded into a disjunction of the queries formed by instantiated all 
the predicate query variables with the permutations of properties in 
the kbs. (It needn't be actually a disjunction, natch, it could just be 
a set, and then if any element of the set is rdf entailed, the query 
succeeds).

My main concern, of course, is make SPARQL relatively neutral for kbs 
expressed in RDF through OWL.

Cheers,
Bijan.

Received on Tuesday, 24 May 2005 15:19:32 UTC