Choosing Classes In Conceptual

abstraction from instances and maximal abstraction . Abstraction from Instances. A class can bedefined only if there are instances in the relevantuniverse possessing all properties defining the class.Adherence to this principle supports the funda-mental meaning of concept —a specification of theproperties common to some instances. If noinstances from the relevant universe share a speci-fied set of properties, there is no “sameness” and noeconomy of representation. It would be cognitivelywasteful to store such a set of properties as a con-cept, as it tells us nothing about the relevant uni-verse.This principle is perhaps obvious for knowledgeacquisition methods that build up abstract descrip-tions from a given set of objects. However, it is lessobvious for methods based on inferring new cate-gories from existing ones [5, 12], as these methodsdo not use instances to identify candidate classes.Moreover, abstraction from instances does notappear as an explicit requirement in object-orienteddesign and semantic data modeling.