On Oct 15, 2014 11:45 AM, "Richard Light" <richard@ <rich...@light.demon.co.uk>light.demon.co.uk <rich...@light.demon.co.uk>> wrote:
I. Properties of properties. > If you do this, the subproperty simply takes the place of the original more generic property in an RDF expression of the statement, and the result is a meaningful RDF triple. If, instead, you try to express "property of a property" as RDF, you find that you are trying to construct a triple with a predicate as its object; something RDF does not allow. This paragraph may confuse some people so I would add some clarifications. 1. It's perfectly ok to make property assertions whose subjects are properties, in both RDF and in OWL 2. These assertions are about the property itself, rather than any particular use of the property. 2. It is possible to make property assertions whose value is a property, in both RDF and OWL. For example one could state that a class has subclasses that are partitioned based on the value of the specified property. 3. In OWL 2 it is possible to add annotations to a property assertion axiom. These annotations are only about the particular act of assertion, rather than what is being asserted. 4. In RDF it is possible to make assertions about an RDF statement by using the RDF reification mechanism. RDF reification is generally considered to be pretty bad (a reified statement does not even entail the original statement). II. Subproperties vs. Reified associations 1. Using subproperties instead of reified entities makes it easier to use off-the-shelf reasoners. For example, if there are constraints that apply to a particular role, it may require creating one or more new subclasses to which the constraints may be applied (these can, of course, be anonymous, but that may not make things easier to use). Additionally there may be optimizations for retrieval of subproperties that are not otherwise available. 2. Using reified associations labelled with concepts from a version of SKOS supporting hierarchical relationships does not automatically entail that hierarchy for the associations. III. Roles and subevents. It is possible to treat subevents as a subclass of roles, but the typical motivation would be if the sub-event was an event in its own right. See eg. http://www.cyc.com/tutorials/roles-and-event-predicates IV. Other meanings of "Role" in applied ontology. Some schools of thought use the term Role to refer to things like a being a Producer. Because some person may not always be or have been a Producer, they do not consider it appropriate for that individual to be an instance of Producer. DOLCE and related work tend to follow this approach. An alternative is to treat the person-as-producer as a subpart of the person, or to treat class membership as holding in an interval.
