Semantic Web for the Working Ontologist, 2nd Edition

Unsatisfiable Classes

A contradiction arises when the assertions that have been made simply cannot all be true. There is a fundamental disagreement in the asserted statements. A similar situation can arise when we define a class in an inconsistent way. A slight variation on the previous example shows how this can happen. First, suppose we define the class of people who own Judy Garland movies that Rocky claims to be a member of:

Now, instead of claiming that Rocky is a member of both this class and JamesDeanExclusive, let’s define the class of such people:

Rocky has claimed to be a member of this class; this claim led to a contradiction.