- From: Ian Horrocks <horrocks@cs.man.ac.uk>
- Date: Tue, 12 Feb 2002 11:53:53 +0000
- To: Steven Gollery <sgollery@cadrc.calpoly.edu>
- Cc: www-rdf-logic@w3.org
On February 11, Steven Gollery writes: > > > > Ian, > > > > It seems to me that the concept of "order" is fundamental in describing > > elements of many ontologies. Why was the decision made not to include this in > > DAML? > > > > Steven Gollery > > > > Obviously, this is an overstatement. It is perfectly possible to define the equivalent of a > linked list, as DAML-S does in its "nextProcessComponent" property, which provides a notion > of "order". What I was really wondering here is: why was the decision made that a daml:list > would be unordered? daml:list is part of the syntax of the language and is used to represent sets of classes, e.g., in a conjunction. As you know, sets are not ordered. Ian > > Steven Gollery > > > > > Ian Horrocks wrote: > > > > > On February 6, Steven Gollery writes: > > > > I'm working on an ontology in DAML that includes some geometric > > > > concepts. I would like to be able to somehow define a property Vertices > > > > whose domain is the Polygon class and whose range is ordered collections > > > > of instances of the Point class, where the length of the ordered > > > > collection is at least three. > > > > > > > > It would be fairly straightforward to say that each Polygon must have at > > > > least three values of a Vertex property which is restricted to class > > > > Point, but that would lose the idea the vertices have an order -- the > > > > order is obviously a fundamental part of the semantics for the polygon. > > > > > > > > Does DAML provide any way to restrict the number of elements in a list? > > > > Or is there some other way to do what I need here? > > > > > > There is no language construct that supports this - properties of a > > > DAML class are always unordered. One possible solution is to make the > > > range of Vertex a more complex structure that describes both the point > > > and its place in the list. This is not completely satisfactory as it > > > is difficult to ensure that the list values are sensibly ordered. > > > > > > Another solution is to define subproperties of Vertex called Vertex1, > > > Vertex2 etc., each being a unique property (i.e., functional). The > > > main disadvantage with this method is that the maximum number of > > > vertices must be decided a priori. Ensuring that values are sensibly > > > ordered is a little easier in this case because the functionality > > > already precludes the case where there is more than one vertex with > > > the same number. Simply asserting, for each n from 2 to the max vertex > > > number, that the existence of the property Vertexn implies the > > > existence of the property Vertexn-1 should be enough to ensure that > > > there are no "gaps" in the list of vertices. > > > > > > Hope this helps. > > > > > > Ian Horrocks > > > > > > > > > > > Thanks in advance, > > > > > > > > Steve Gollery > > > > sgollery@cadrc.calpoly.edu > > > > > > > > > > > > ------------------------------------------------------------------------ > > > > * Previous message: Ian Horrocks: "Re: DAML: restricting number of elements in a list" > > * In reply to: Ian Horrocks: "Re: DAML: restricting number of elements in a list" > > * Messages sorted by: [ date ] [ thread ] [ subject ] [ author ] > > * Other mail archives: [this mailing list] [other W3C mailing lists] > > * Mail actions: [ respond to this message ] [ mail a new topic ] >
Received on Tuesday, 12 February 2002 06:47:45 UTC