- From: Thomas B. Passin <tpassin@comcast.net>
- Date: Sun, 15 Jun 2003 11:12:49 -0400
- To: www-rdf-interest@w3.org
[Roger L. Costello] > Jos De_Roo wrote: > > > > we tend to use RDF interpretation properties for that > > and math: properties and N3 conversion rules such as eg > > > > {?X eg:length-in ?Y} => {?X eg:length-cm (?Y 2.54).math:product}. > > {?X eg:length-cm ?Y} => {?X eg:length-in (?Y 2.54).math:quotient}. > > [snip] > > Hi Jos, > > Does this have an XML syntax? My interest is in how to express the > mathematical relationships using an XML syntax. /Roger Applying units involves modeling them, and that involves more than one aspect. I think that it is pointless to declare equivalence between instances of variables. Something more general is needed. Also, a simple scale factor is one thing, but there are often more complex relatoinships involved. A unit is like data type, but not a lexical one. As long as we restrict ourselves to scalar quantities that would be expressed in floating point numbers of some flavor, it seems to me that we could derive new types from the XML Schema data types. Thus we could derive a type "Meter" from type "Decimal", and so on. The lexical representation would be unchanged. Since these new types would be derived from XML Schema, presumably they would be suited for use in RDF. Next, I would model each conversion as a separate resource - {&units;inch-to-cm-conversion {&units;baseUnit, &units;Inch} {&units;targetUnit, &units;Cm} {&units;scaleFactor, xs:decimal:2.54} } This is a simple, clean approach that says exactly what is intended, and could be applied by a processor that understands the constructions. No instances of actual physical quantities have to be annotated with equivalent conversion factors or equivalent values in several units. The only requirement would be the ability to derive datatypes like Inch, and this can be done with XML Schema datatypes. Obviously an OWL processor would not know what to do with these statements and would not be able to reason with them to see if a particular conversion were correct or not. But that is not OWL's job, anyway, IMHO. If Roger wants to extend an OWL processor to understand scalar conversions, I suppose he can do so. But any attempt to logically test equality between different numerical measures is going to be very difficult, because of the lack of infinite precision, and different computing errors and precisions. A non-trivial undertaking, I think, and one that is not in the domain of ontology. Cheers, Tom P
Received on Sunday, 15 June 2003 11:10:44 UTC