316 12 Building Bioinformatics Ontologies
benign and are unlikely to have much effect on programs. Adding new at-
tributes and relaxing constraints are usually innocuous. Some of the more
substantial modifications include:- Modifying property domains and ranges. A set of properties on sub-
classes can be changed to a single property on a superclass, or a property
on one class can be shifted to become a property on a related class. - Reification. This is the process whereby concepts that are not classes are
given class status. For example, a relationship can be reified to become a
class. Reifying a relationship will replace the relationship with a class and
two relationships. - Unreification. This is the reverse of reification.
Figure 12.2 Part of the medical chart ontology.As an example of ontology evolution, consider the medical chart ontol-
ogy. In the part of the design shown in figure 12.2, thetemperatureof
Patientis unrelated to any event. The problem is that the body tempera-
ture of a patient could be important information for events. A prescription
could be based, in part, on a temperature measurement, but the current body
temperature could differ from the temperature when the test was performed.
To deal with these possibilities, the design should be modified as shown in
figure 12.3.
As another example of ontology evolution, it is a common practice to mea-
sure the body temperature of a patient at many significant events, not just
during tests. To allow for such a measurement for other events, one could