OntoClean
OntoClean is a methodology for analyzing ontologies based on formal, domain-independent properties of classes (the metaproperties) developed by Nicola Guarino and Chris Welty.
Core concepts
Rigidity1
Rigidity is based on the notion of essence. A class is rigid for an instance if the latter could not exist if it wasn’t an instance of that class, in all worlds and at all times.
- Rigid classes: Human
- Anti-rigid classes: Student, Food
- Semi-rigid classes: HardThing (essential to hammers but not to sponges)
Identity1
Identity refers to the problem of determining whether or not two entities are the same. A class with identity is one where all instances can be identified as themselves, based on some identity criterion provided either by the class or a superclass of it.
- Classes have identity: Person
- Classes don’t have identity: RedThing
Unity1
- Unity: Pacific ocean
- Non-unity: One gallon of water
- Anti-unity: Legal agent (this can include both people and organizations that have different unity criteria)
Dependence1
We say that a class C1 is dependent on a class C2 if for every instance of C1 an instance of C2 must exist. An example of a dependent class is Food, because instances of food can only exist if there is something for which these instances are food. For example, if tomorrow we all stop eating bananas, then the concept of Banana will no longer be considered an instance of Food. This does not mean that bananas cease to exist the moment we stop eating them—they just stop having the role of food.