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306 12 Building Bioinformatics Ontologies

Alternatively, if one is using OWL, then theeventTypeproperty is defined

in the ontology as follows:

<owl:ObjectProperty rdf:ID="eventType">

<rdfs:range>

<owl:Class rdf:ID="EventType">

<owl:oneOf parseType="Collection">

<EventType rdf:ID="Admission"/>

<EventType rdf:ID="Test"/>

<EventType rdf:ID="Prescription"/>

<EventType rdf:ID="Operation"/>

</owl:oneOf>

</owl:Class>

</rdfs:range>

</owl:ObjectProperty>

Choosing between subclassing and property values can be difficult, and

it can be dependent on the purpose of the ontology. As a result, different

ontologies, ostensibly about the same domain, may use different designs.

There are a number of criteria that can help one make this design decision:

1. Intrinsic vs. extrinsic properties.Generally speaking, extrinsic property val-
   ues should be designed as property values rather than subclasses. For
   example, people are often classified into groups according to their ages,
   such as Infant, Toddler, Adolescent, and Adult. However, the age of a
   person is constantly changing so it is normally considered to be extrinsic.
   Thus the age group is better handled using a property value rather than
   as a subclass.


2. Exceptions.Subclasses have the important characteristic ofinheritance.This
   was already explained in the introduction to section 12.6. If one wishes to
   allow exceptions, then it is better to use property values to distinguish
   cases.


3. Subclasses have new properties.When a subclass will have additional fea-
   tures, such as an additional property, then it is better to use subclassing
   rather than property values. For example, in the Event classification of the
   medical chart ontology, one would expect that each of the subclasses will
   have properties unique to the subclass. For example, a prescription in-
   stance will have a drug and administration schedule, which other events,
   such as an admission, would not have. However, this criterion is not as