From: Ian Horrocks <horrocks@cs.man.ac.uk>

Date: Tue, 19 Feb 2002 16:02:14 +0000

Message-ID: <15474.30470.215390.687902@galahad.cs.man.ac.uk>

To: Steven Gollery <sgollery@cadrc.calpoly.edu>

Cc: www-rdf-logic@w3.org

Date: Tue, 19 Feb 2002 16:02:14 +0000

Message-ID: <15474.30470.215390.687902@galahad.cs.man.ac.uk>

To: Steven Gollery <sgollery@cadrc.calpoly.edu>

Cc: www-rdf-logic@w3.org

On February 11, Steven Gollery writes: > Ian, > Steven, The language aims to provide only basic building blocks and leaves it up to the user to determine how they want to represent more complex concepts (like order) - as I mentioned in earlier email, you can represent (some aspects of) order in a variety of ways, e.g., by describing your own list structure. 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 > > 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 > > > > > >Received on Tuesday, 19 February 2002 10:55:18 UTC

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