W3C home > Mailing lists > Public > www-rdf-logic@w3.org > May 2001

RE: Why Triples? (was Re: What do the ontologists want)

From: pat hayes <phayes@ai.uwf.edu>
Date: Sat, 19 May 2001 16:25:13 -0500
Message-Id: <v04210142b72c93c1d464@[205.160.76.183]>
To: "Danny Ayers" <danny@panlanka.net>
Cc: www-rdf-logic@w3.org
>Nice to see something real-world for a change. However, you only go 
>as far as to discuss representing or encoding (correct word?) the 
>the data in triples. There's no denying that the structure would be 
>a bit tangled, but look at what we might want to do with it - 
>communicate & reason. Ok, we could pass on 4-ary relations, as long 
>as the receiver was prepared to accept 4-ary structures. How might 
>it be transferred?

Any number of ways. You could do it in XML, for example. You could do 
it using Sexpressions, or even in HTML if you were willing to write a 
(very) simple parser.  What kind of transfer problems are you worried 
about?


>Same with reasoning - how would you go about querying this alongside 
>e.g. a list of Director, Age Restriction, Country of origin, 
>Duration + another 4 sets I can't think of...

Reasoners have been using formats like this since the 1960s. You 
would unify the two expressions from left to right.

>I also suspect that there is something happening at a psychological 
>level in these arguments - it's far easier for a human to relate to 
>information in a structure like that below - but is this necessarily 
>the case for machines?

Yes, there are significant computational advantages. In general, the 
more stuff you can incorporate into the unifier, the more efficient 
the inference search: you tend to be trading an exponential for a 
linear cost, a very good trade.

Pat Hayes

>
>
>---
>Danny Ayers
><http://www.isacat.net/>http://www.isacat.net
>
>-----Original Message-----
>From: www-rdf-logic-request@w3.org 
>[mailto:www-rdf-logic-request@w3.org]On Behalf Of Ziv Hellman
>Sent: 19 May 2001 23:18
>To: Sandro Hawke
>Cc: www-rdf-logic@w3.org
>Subject: RE: Why Triples? (was Re: What do the ontologists want)
>
> > There's no reason a set of triples like
> >
> >    <a, color, red>
> >    <a, size, big>
> >    <a, flavor, sweet>
> >    <b, color, green>
> >    <b, size, small>
> >    <b, flavor, bitter>
> >
> > can't be presented to users as
> >
> >    object   color   size   flavor
> >    ======   =====   ====   =====
> >      a      red     big    sweet
> >      b      green   small  bitter
> >
>
>This is a nice example, but if you examine it closely you will 
>notice that it does not represent a true multi-ary relation, but 
>rather a serialization of natural binary relations: an object has a 
>colour, it has a size, it has a flavour, and each of these is an 
>attribute of the object. In this case, the table can be directly 
>reduced to the triples, and vice-versa. Add price to the list later, 
>and you have just tacked on yet another binary predicate.
>
>But consider the following more complicated table that one might 
>encounter in real life and want to make available on a semantic web:
>
>
>month           city            cinema  theatre         film
>-------         ----------      -----------     ------------ 
>---------
>
>April           Tel Aviv        Globus  1                       Pokemon 2
>April           Tel Aviv        Globus  1                       Gladiator
>April           Tel Aviv        Globus  2                       Miss 
>Congeniality
>April           Tel Aviv        Peer            1 
>Miss Congeniality
>April           Tel Aviv        Peer            2 
>Cast Away
>April           Jerusalem       Gil             1 
>Pokemon 2
>April           Jerusalem       Gil             2 
>Proof of Life
>April           Jerusalem       Globus  1                       15 Minutes
>April           Jerusalem       Globus  2                       102 Dalmatians
>May             Tel Aviv        Globus  1                       Pokemon 2
>May             Tel Aviv        Globus  1                       Billy Elliot
>May             Tel Aviv        Globus  2                       The Mummy
>May             Tel Aviv        Peer            1 
>The Mummy
>May             Tel Aviv        Peer            2 
>Exit Wounds
>May             Jerusalem       Gil             1 
>Pokemon 2
>May             Jerusalem       Gil             2 
>The Mummy
>May             Jerusalem       Globus  1                       A 
>Hard Day's Night
>May             Jerusalem       Globus  2                       15 Minutes
>
>
>Unfortunately, no matter how one views this, there is no way to 
>reduce the information content here to binary attributes. In order 
>to encode it as ground atom triples, one would probably artificially 
>have to create 18 objects, each of which would then be associated in 
>a binary relation to each basic item in the table. The resulting 
>data construct would look so baroque and/or contain so much 
>redundancy that I would guess someone somewhere will eventually 
>notice that RDF has containers and decide to ship the table more 
>straightforwardly as a list of lists and by-pass the triples 
>altogether.
>
>
> > The best reasons I've heard for triples:
> >
> >      We don't want to grant any particular properties or relations
> >      special status. 
> >
> > If we later want to add a property (column) "price" or even "price at
> > Whole Foods Market in Newtonville on 2001-05-18" we can do that
> > without breaking anything.
>
>In the cinemas example above, it is not immediately clear that 
>adding new triples somewhere deep in a complicated triple encoding 
>of the data is easier -- or less likely to break anything -- than 
>tacking on a new value at the end of each list in a list of lists 
>encoding.
>
>
>Cheers,
>
>Ziv
>
>

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Received on Saturday, 19 May 2001 17:25:12 UTC

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