Page 126 - DCAP506_ARTIFICIAL_INTELLIGENCE

Artificial Intelligence

Notes

Here the frames Person, Adult-Male, Rugby-Player and Rugby-Team are all classes and the frames
Robert-Howley and Cardiff-RFC are instances.

Notes
 The isa relation is actually the subset relation.
 The isa attribute possesses a transitivity property. This shows: Robert-Howley is a Back
and a Back is a Rugby-Player who in turn is an Adult-Male and also a Person.
 Both isa and instance have inverses which are known as subclasses or all instances.
 There are attributes that are connected with the class or set such as cardinality and on
the other hand there are attributes that are owned by every member of the class or
set.

Distinction between Sets and Instances

It is significant that this difference is evidently understood.
Cardiff-RFC can be considered of as a set of players or as an instance of a Rugby-Team.

If Cardiff-RFC were a class then
 its instances would be players
 it could not be a subclass of Rugby-Team or else its elements would be members of Rugby-
Team which we do not desire.
Rather we make it a subclass of Rugby-Player and this permits the players to inherit the accurate
properties facilitating us to allow the Cardiff-RFC to inherit information regarding teams.

This means that Cardiff-RFC is an instance of Rugby-Team.
But there is a difficulty here:
 A class is a set and its elements contain properties.

 We wish to use inheritance to confer values on its members.
 But there are properties that the set or class itself has like the manager of a team.

120 LOVELY PROFESSIONAL UNIVERSITY