Re: [all] OWL and RDF compatibility scribles

Michael Kifer wrote:
>> Attached is a slightly modified version of the SW compatibility breakout notes
>> in PDF form.  I added a key for the labels I used for the speakers.
>>
>> -Evan
> 
> I have a Q regarding one of the remarks that Bijan made (according to the
> notes). Posting here because there might be wider interest in this.
> 
> There was a discussion of whether the query language (SPARQL) has negation
> and Bijan said that the existentials get us there.
> This is something that I don't understand. *Universal quantification* in a
> query language introduces negation. But existential conjunctive queries
> without explicit negation are Horn clauses and are within Datalog.
> For those queries the classical equivalence of logical implication, least
> fixpoint, and the unique min model holds.


I am not sure if this bit of SPARQL is relevant.
If not please ignore.

From
http://www.w3.org/TR/2005/WD-rdf-sparql-query-20051123/

[[
One may test that a graph pattern is not expressed by specifying an 
optional graph pattern that introduces a variable and testing to see 
that the variable is not bound. This is called Negation as Failure in 
logic programming.

This query matches the people with a name but no expressed date:

PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX dc:   <http://purl.org/dc/elements/1.1/>
SELECT ?name
  WHERE { ?x foaf:givenName  ?name .
          OPTIONAL { ?x dc:date ?date } .
          FILTER (!bound(?date)) }

Query result:
name
"Alice"
]]

Jeremy