- From: Uche Ogbuji <uche.ogbuji@fourthought.com>
- Date: Tue, 15 May 2001 10:06:56 -0600
- To: Peter Crowther <peter.crowther@networkinference.com>
- cc: "'pat hayes'" <phayes@ai.uwf.edu>, Jonathan Borden <jborden@mediaone.net>, www-rdf-logic@w3.org
> > From: pat hayes [mailto:phayes@ai.uwf.edu] > > [Jonathan Borden wrote:] > > > Certainly being able to quote statements/triples is useful > > > ... indeed a practical requirement. > > > > Can you (or anyone) say why the ability to quote is considered a > > practical necessity? From where I am standing it seems an arcane and > > exotic ability, not one that is of central practical importance. What > > is the practical utility of being able to refer to a predicate, > > rather than use it? > > I've got sympathies on both sides of this, based on past and present systems > I've used; summarised below. I'm also pretty hard-nosed about why I'm doing > this; summarised in the last paragraph. > > Some systems are more obvious to design if there is a facility to make a > statement about a statement. Almost always, these are attributions: the > typical example seen on this list, and the examples we used in SMK, are of > the form "X says 'statement Y'". (Question: Can anyone come up with a > different use for reification? If this is the only special-case, should > there be a different mechanism for attribution?) ? The RDF spec itself has a different use case. Furthermore, all the uses are pretty old hat (at least on www-rdf-interest). I'm sure I'm mising something, but just in case, general categories include Attribution: your "Midwinter Spring is its own season", says Eliot Quantification: Temperatures are in the high 30s (in degrees centigrade) Qualification: "The check's in the mail", he lied (OK, it's attribution+qualification, but I like the example) Examples that fall into the above bin include Temporal placement: 1980: The capital of Nigeria is Lagos; 1990: The capital of Nigeria is Abuja Confidence factors: There is a 15% likelihood that Malaria results in death. > We were working with clinical systems, where the ability to attribute > particular statements to clinicians was of legal importance in case of > lawsuits. No attribution, no adoption of system. We chose to implement > this using reified triples; this opened up a can of worms as far as the > implementation was concerned, as we could then make statements about the > statements of attribution, and we could also construct self-referencing > systems such as: > > #2 writtenBy peter (triple ID #1) > #1 writtenBy peter (triple ID #2) > > Overall, the approach caused more problems than it solved; GRAIL and the > more recent work at the University of Manchester dropped this facility, and > we put in special-case code for dealing with attribution. I think the answer to these problems are effective tools. Rules-based systems should be able to operate on the metadata making up attributions to set sensible limits ("sensible" being determined by the field of use). > However, we were dealing with a knowledge base that was totally under our > control. One of the interesting features of RDF is that it allows an author > to mark up a source over which they have no direct control; one view of > search engines and classifications like Yahoo! is that they will evolve into > huge metadata repositories rather than simply free-text engines. In this > situation, there are a couple of areas that need thought: > > 1) How does a third party refer to portions of another's work? Especially > if that work is RDF? For example, I might want to say that I agree with all > the statements in a particular document except statements A, B and C. Well, while this is rather cumbersome in RDF, it's quite possible. You can either list all the statements you agree with, or provide an exception predicate which overrides a statement of agreement with the whole document. > 2) (a) Should one be able to reason about such statements / does it gain us > anything; (b) How should one be able to reason about such statements if it > does gain us anything? > > Apart from these areas, I agree with Pat: it is an arcane and exotic > ability. It is also an ability that will cost us very dearly in terms of > being able to reason about the resulting (rather baroque) structures. Hmm. I understand how reification can complicate matters, but I don't see it as being more insurmountable than the complexity of distributed ontology in the first place. -- Uche Ogbuji Principal Consultant uche.ogbuji@fourthought.com +1 303 583 9900 x 101 Fourthought, Inc. http://Fourthought.com 4735 East Walnut St, Ste. C, Boulder, CO 80301-2537, USA Software-engineering, knowledge-management, XML, CORBA, Linux, Python
Received on Tuesday, 15 May 2001 12:08:06 UTC