Microworlds
It seems natural that our knowledge in this world can be broken down to particular microworlds , within each the knowledge is expressed in terms of classes and their properties.
A microworld is a description of some particular thing, usually expressed in just enough detail to make interactions possible. Anything that a human's common sense may know can be an example of a microworld, including a board game like chess, or a family tree?.
Such an indication in John McCarthy's Advice Taker inspires us to to think knowledge representation should naturally be in terms of classes and their properties, better known as Object Oriented programming in computer science.
Describing a microworld comprises definition of classes and their properties. Qualifications or dynamic properties are defined to assign attribute to objects depended on the status of the microworld. Relative Qualifications are names of relations we attribute between two objects also based on the status of the microworld. Actions that can bring change in the state of the microworld, and rules are defined to indicate the governing rules of such actions. Goals can be defined to indicate a desired state of the microworld for a particular class, and finally heuristics help the class to get closer to their goal? states when search trees are too large to be solved entirely.