- From: pat hayes <phayes@ai.uwf.edu>
- Date: Sat, 19 May 2001 16:12:27 -0500
- To: "Ziv Hellman" <ziv@unicorn.com>
- Cc: www-rdf-logic@w3.org
- Message-Id: <v04210140b72c9053062d@[205.160.76.183]>
> > 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. Well, no, there IS a way, as you go on to describe, if you are willing to introduce new entities. >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 problem is that it will stop looking baroque when you get used to it. The transformation involving the 18 objects can be done uniformly in the same way to all relations, and the same binary attributes can be used for them all (basically you need an attribute to select the m-th item in an n-tuple, for each m <= n.) Once someone gets used to this style of writing things it can come to seem natural, rather in the way that one can get used to a bad smell if it there all the time. So the argument is basically aesthetic rather than slam-dunk technical. Anyone who can live with XML isnt going to get all upset by a linear increase in notational complexity. > > 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. Yes, I agree. The variable polyadic notation I mentioned that KIF uses can be described as every relation being defined by a set of lists (of arbitrary finite length) rather than a set of n-tuples. Pat Hayes --------------------------------------------------------------------- IHMC (850)434 8903 home 40 South Alcaniz St. (850)202 4416 office Pensacola, FL 32501 (850)202 4440 fax phayes@ai.uwf.edu http://www.coginst.uwf.edu/~phayes
Received on Saturday, 19 May 2001 17:12:24 UTC