Types and Classes
- A type is a time-invariant description of a set of possibly complex values. A type can thus be a base type of structured; no specific operations are bound to a type apart from generic ones. A type in an OODBS only describes the structural part of a class.
- A class encapsulates structure and specific behavior. Moreover, class is a run-time concept such that the set of objects in existence at a given point in time, the so-called instances, can be allocated to it as its extension.
If the objects of class
K1 are more special than those of class K2, K1 will be defined as a subclass of K2 with the effect that K1 inherits the structure of K2.
- Without inheritance, six programs must be written for the following two objects:
- Using inheritance, only four programs are needed:
| I’ve locked the door. They’re as safe as houses (very safe). |