- From: W. E. Perry <wperry@fiduciary.com>
- Date: Sat, 26 Apr 2003 11:47:35 -0400
- To: "Roger L. Costello" <costello@mitre.org>
- Cc: www-rdf-interest@w3.org
Hi Roger. My very different take on the role of semantics in a universal internetwork of complementary and interdependent processes: We can agree entirely on the headline of your slides #7 and #8: "Meaning (semantics) applied on a per-application basis". This is precisely how semantics are elaborated: as the outcome of specific expertise applied through process. It is, however, in the nature of expertise to be idiosyncratic. The most valuable semantics for a given purpose are elaborated from the application of the most specific expertise. Therefore the 'problem' which you would highlight in your slide #9 ('problems with burying the semantic definitions within each application') is in fact an inherent property of expert processes. In order to apply expertise, processes must comprehend a specific expert semantics of the data upon which they operate and the nature of their manipulation of that data. In your slide #9 you quite correctly factor an application of expert process into code to interpret the data and code to process the data. That 'interpretation' of the data is a specific instantiation of the particular semantically-freighted datastructure upon which a given expert process expects to operate. The 'code to process the data' has to be designed for a particular instantiation of the data. The more particular the expertise of that process, the more particular and idiosyncratic--and less the common denominator of a standard semantic vocabulary--must be the instantiation of, and therefore the semantics implied by, the data upon which that process operates. Your example on slide #9 of the Mars probe disaster--one application interpreted the data in inches, another application interpreted the data in centimeters--is actually a counterexample to what you hope to illustrate. The cause of the disaster was that different applications expected to share *common* semantics: that the data as given was, for the purposes of *both* applications, in inches or in centimeters. The devastating error was that each application deferred from its own expertise to a presumed agreement or 'semantics in common' about which *both* applications were fatally mistaken. It does not matter which application happened to guess or blithely presume correctly about the units of the data as presented. It was an unconscionable abdication of the expertise of both applications to make any such presumption. As you correctly illustrate on your slide #9, there are two necessary components to an expert application, and the first of them is code to interpret the data. Part of the application's own expertise is knowledge of the units in which it expects to operate, and therefore it is crucial for the application to instantiate data in those units for its own purposes. And, in turn, crucial to doing that is first recognizing the units intended or implied in data as received, in order to elect the correct expertise for instantiating data in the units required. The usual clues for such recognition or syntactic, which is why I can say that in your example you have inferred the line between syntax and semantics in the wrong place. An easy case would be if the units were explicitly presented in syntax, as with e.g. an inches attribute or a units element. Occasionally it is in fact as simple as that, and the application can, through its expert interpretation code, readily resolve the units presented syntactically into those required semantically. In other cases, the application must look at the provenance or structure of the data as received and compare it with either or both in previous examples that it has encountered in order to make an expert interpretation of the data received. The point is that it is always incumbent on the application by virtue of its presumed expertise to make its independent interpretation of the data received in order to make an informed instantiation of the data required. To defer in that necessary task of expert processing to some presumed common semantics is to abdicate expertise itself, and the predictable outcome is error. Perhaps we should consider a different example. Suppose that an instance of your SLR is presented to an application for customs duty collection. The task of that application is not to infer that an SLR is a sort of camera but to infer that the particular instance presented is an example of dutiable luxury consumer goods. This application is a valuable use of the SLR/camera ontology which you are creating, but probably not one which you expected, nor one which you have provided 'hooks' for in the ontology you are building. Yet our larger purpose here is to build (and more abstractly to build the principles for) ontologies distributed among processing nodes on a worldwide internetwork. In that effort, harnessing the unique perspective and uniquely expert processing at each node is the particular value we hope to add by building out the ontology to worldwide scale. Clearly the customs application cannot function without its own ontological distinctions between dutiable and non-dutiable, consumer and industrial goods. Equally clearly we do not want to burden every camera hobbyist's SLR ontology with the distinctions which are most crucial to the customs agent. The only workable way to reconcile those goals, and the only way to build out any non-trivial ontology to worldwide scale, is to require as a matter of design that semantics are locally elaborated to fill the local needs of expert processes. Being local means that these semantics are not shared, nor understood in some common way. While it is entirely possible that congruent semantics might be elaborated in separate locations by locally appropriate processes, the point is not the similarity of the semantics but the idiosyncrasy of the processes which elaborate them. Respectfully, Walter Perry "Roger L. Costello" wrote: > Hi Folks, > > I have created a few slides to describe, at a high level, the > motivation for using OWL: > > http://www.xfront.com/owl/motivation/sld001.htm > > Comments welcome. /Roger
Received on Saturday, 26 April 2003 12:03:13 UTC