W3C home > Mailing lists > Public > public-sparql-dev@w3.org > October to December 2007

Re: Simple example of need for negation operator

From: Bob MacGregor <bob.macgregor@gmail.com>
Date: Tue, 11 Dec 2007 08:28:46 -0800
Message-ID: <a0d0f8f70712110828x60a9a236h14d1f701c1422d7d@mail.gmail.com>
To: "Lee Feigenbaum" <lee@thefigtrees.net>
Cc: public-sparql-dev@w3.org
Hi Lee,

Your example does the job.  I have to congratulate you on your proficiency.
I do
have a couple of questions.  One, the construct you are using is doing a max
computation.  The (much simpler) construct I used did not (and there is no
max
in the conceptualization of the quuery).  Also, when your
example executes, there will be a small cross product computed between the
different tags attached to each article.  In my example, its a linear scan.
I'm
wondering if it the cross product is necessary in SPARQL, or if there is
another
way to capture this example that is more efficient and closer to the true
semantics
of the query.

Second, I'm wondering about the general case of universal quantification.  A
simple example would be something like  "select people all of whose children
are male".  I'm being lazy here, since I could search  the sparql-dev
threads
looking for the solution.  Do you have one at your fingertips that you can
point
me to?  In our language, this would be

select ?person
from model
where (?person rdf:type Person) AND
          UNSAID ((?person hasChild ?child) AND
                        UNSAID (?child gender "Male"))

Cheers, Bob


On Dec 10, 2007 11:24 PM, Lee Feigenbaum <lee@thefigtrees.net> wrote:

> Bob MacGregor wrote:
> > Hi Lee,
> >
> > OK, we'll try sparql dev, as long as this is a how to, rather than a
> > "can't be
> > done".  But it looks to me like
> > your query returns no bindings if an article does not have a timetag.  I
> > say this because of the {?a ex:timetag ?maxtime} clause
> > that comes before the OPTIONAL.  But in that case, it should return
> > the article.  Can you fix this, or is it not expressible after all?
>
> Right, I did that purposefully to concentrate on the "max" idiom. If you
>  want to include articles with no timetag, it becomes:
>
> PREFIX : <http://example.org/>
> SELECT ?a
> FROM <http://thefigtrees.net/lee/sw/data/times.ttl>
> WHERE {
>   ?a a :article .
>   OPTIONAL {
>     ?a :timetag ?maxtime .
>     OPTIONAL {
>       ?a :timetag ?othertime . FILTER(?othertime > ?maxtime)
>     }
>     FILTER (!bound(?othertime))
>   }
>   FILTER(!bound(?maxtime) || ?maxtime < 5)
> }
>
> The key is, I guess, to make the whole "find the max time" part optional
> and then filter outside that on "there is no maxtime or the maxtime is
> early enough".
>
> (Note, I put some actual data at the above URL so that you can try this
> out. To do this I changed the predicate names a bit and used integers
> instead of datetimes for simplicity. I made "now" equal to 5. :-) ARQ
> deployed at http://sparql.org is a great place to try it.)
>
> The data is:
>
> @prefix : <http://example.org/> .
>
> :onetimeOK a :article ; :timetag 1 .
> :onetimeNotOK a :article ; :timetag 10 .
> :twotimesOK a :article ; :timetag 1, 2 .
> :twotimesNotOK a :article ; :timetag 1, 10 .
> :notimeOK a :article .
>
>
> ... and when I run the above query through ARQ at sparql.org I get:
>
> a:
>         <http://example.org/notimeOK>
>         <http://example.org/twotimesOK>
>         <http://example.org/onetimeOK>
>
>
> Lee
>
> >
> >
> >     In SPARQL, this query is (unedited, untested):
> >
> >     SELECT ?a
> >     FROM :model
> >     WHERE {
> >       ?a rdf:type ft:article ; ex:timetag ?maxtime .
> >       OPTIONAL { ?a ex:timetag ?othertime . FILTER(?othertime >
> ?maxtime) }
> >       FILTER (!bound(?othertime) && ?maxtime > '...now...')
> >     }
> >
> >     Original target:
> >
> >
> > SELECT ?a
> > FROM model
> > WHERE
> >      (?a rdf:type ft:Article) AND
> >      UNSAID ((?a ex:timetag ?time) AND
> >                    (?time > $NOW))
> >
> > =====================================
> > Robert MacGregor
> > Chief Scientist
> > Siderean Software, Inc.
> > bob.macgregor@gmail.com <mailto:bob.macgregor@gmail.com>
> > Mobile: 310-469-2810
> > =====================================
>



-- 
=====================================
Robert MacGregor
Chief Scientist
Siderean Software, Inc.
bob.macgregor@gmail.com
Mobile: 310-469-2810
=====================================
Received on Tuesday, 11 December 2007 16:28:55 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Tuesday, 8 January 2008 14:17:05 GMT