W3C home > Mailing lists > Public > www-rdf-interest@w3.org > August 2004

Re: query!

From: Richard Newman <r.newman@reading.ac.uk>
Date: Tue, 31 Aug 2004 18:11:50 +0100
Message-Id: <D91EDEA6-FB70-11D8-BBE5-000A957D9564@reading.ac.uk>
Cc: rdf-interest <www-rdf-interest@w3.org>
To: go4chaitu_eng@yahoo.co.in

I believe you intended to send this to the list, so I shall CC my reply.

An application of FOAF: there are many! Think of any domain which 
attempts to model people.

- An address book application
- Social network software
- Putting contact details on the Web
- etc.

There will doubtless be other FOAFers on the list who can give you more 
examples.

Reification is described in the RDF docs. Essentially, it's 
instantiating a concept ("improperly making something an object"); the 
typical use is to make it possible to refer to statements. E.g.

x p y

can be reified into

_a a rdf:Statement
_a rdf:subject x
_a rdf:predicate p
_a rdf:object y

We can now make statements about _a. Note that this does NOT assert "x 
p y". It's like saying "John said "Paul's car is red"" --- Paul's car 
is not necessarily red.

-Richard

On 31 Aug 2004, at 18:03, Chaitanya Saragadam wrote:

> Thanx  for clarifying.
> I got it.
> One more request, can anyone give me a good problem definition of 
> FOAF.I mean any good application of FOAF.
> And give me a simple example of what a reification is and how is it
> useful and better than a triple.
> bye.
>
> Richard Newman <r.newman@reading.ac.uk> wrote:
> You would be lying. When I write an RDF file using the FOAF vocabulary,
>  my use of it is essentially a contract: I subscribe to that ontology,
>  which means that when I say foaf:firstName (which expands to
> http://xmlns.com/foaf/0.1/firstName), I mean the person's first name.
>
> If you define your own ontology in that namespace, you're trying to
> speak for someone else --- like claiming your CV is at
> http://microsoft.com/ChaitanyasCV.doc. Furthermore, it won't work: a
> crawler that goes to look up the ontology/schema by hitting
>  http://xmlns.com/foaf/0.1/ won't find your terms.
>
> Example:
> FOAF defines firstName. If you defined favouriteFruit as
>
> ----
> a owl:ObjectProperty ;
> rdfs:range ;
> rdfs:domain .
> ----
>
> Then anyone picking up your RDF file would now have a new FOAF
>  property. That's fine. However, other people who haven't got your file
>  loaded would have no idea about foaf:favouriteFruit, and they couldn't
>  find out by accessing the standard FOAF ontology (which is a bad thing
>  for you!). If you redefined FOAF (rather than extending it), using the
>  same namespace, it's the same as saying you speak English but changing
>  the meaning of the words. Interoperability relies on people using
>  shared terms, and using your own namespace is the chosen way of
> controlling vocabulary.
>
> I think what you're wanting to do is mix terms. The right way to do the
>  above is to put favouriteFruit into your own namespace. You can then
>  reference that ontology in your FOAF files, and describe your 
> favourite
>  fruit. You don't have to only use one namespace. The following is the
>  way to do it:
>
> ----
> @prefix ex:
>  @prefix foaf:
>
>  ex:favouriteFruit a owl:ObjectProperty ;
> rdfs:range ;
> rdfs:domain .
>
> :Me a foaf:Person ;
> foaf:name "Richard" ;
> ex:favouriteFruit ex:Apple .
> ----
>
> There is no incentive to overloading an existing namespace that belongs
>  to someone else; define your own. There is an incentive to using the
>  same terms as everyone else (hence FOAF's popularity), which is how 
> you
>  get interoperability.
>
> There's also no point in restricting namespaces. The Semantic Web is an
> enormous graph; your application should just take the slices out of it
> that it needs. If you only want to look at people, use FOAF; there's no
>  reason why people can't also add other triples into the same file ---
> you can safely ignore them.
>
> Apologies for the long, rambling reply, but I hope that covers what
>  you're trying to ask.
>
> Regards,
> Richard Newman
>
> School of Systems Engineering
> University of Reading
>
> On 31 Aug 2004, at 13:05, Chaitanya Saragadam wrote:
>
> >
> > Hi all,
> > I sent a query few days back and didn't get a good
> > answer for the same.I think i have'nt expressed it
> > correctly.I will try to explain it again.
> > Take an example of FOAF Vocabulary,
> > where a has some properties like
> > , etc.
> > And he gave his namespace as,
> > http://xmlns.com/foaf/0.1/
> > ok,so all the rdf files with foaf tags will be used in
> > searching applications of some subject like person.
> > Now my question is ,
> > i will use the same namespace (ie).,
> > http://xmlns.com/foaf/0.1/
> > but i will define my own properties for a person.I can
> > do it right!
> > And ur search engine will search my file by some
> > crawling mechamism and searches for a specific
> > property
> > of a person which wouldnt be avaliable as it is
> > defined by me.
> > So, what is the purpose of writing searching
> > applications if i cannt restrict the namespaces to be
> > used.Is there any body governing that?
> > If not no one sticks to a spec as they define their
> > terms according to their applications and so their
> > needs will be satisfied but not a solution for global
> > applications.
> > Please clarify this , even now if u cant understand, i
> > will explain it still more clearly.
> > But i hope u people got my point.
> > Thanx for helping,
> > bye.
> >
> >
> >
> > __________________________________
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Received on Tuesday, 31 August 2004 17:12:16 UTC

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