Class Categories

The classes can be divided in to three categories
• analysis classes
• design classes
• implementation classes

Analysis classes
An analysis class describes a data abstraction directly drawn from the model of the external system. PLANE in a traffic control system, PARAGRAPH in a document processing system, are typical examples.

Any software system is based on an operational model of some aspect of the external world. So to simulate the real world things, there should be a way. The analysis class can either be abstract or not. Here it’s important the way we look at the external object. We should look at the object in the system’s point of view.

Implementation classes
An implementation class describes a data abstraction introduced for the internal needs of the algorithms in the software, such as LINKED_LIST or ARRAY.
When we implement the system we have to think about various ways of structuring the objects. This is coming under “Data Structures and Algorithms”.

Differed Implementation Classes
This is a subset of implementation classes. Although the traditional books emphasize about the fully implemented classes in practice we may not be able to use them as it is. The implementation classes are quite abstract, for a broader usage. For example, various queue implementations will be descendants of a deferred class QUEUE describing the abstract concept of sequential list.

Design Classes
Design classes are new set of classes introduced by the architecture to produce an elegant and extendable software structures. STATE, COMMAND type of classes are falling in to this category. Controller classes that are being used in MVC are also fall in to this category

Out of the above types of classes Analysis classes belong to the problem space. Since those classes are found in the problem space. But the other two are in the solution space. When providing the solution, the architecture introduces those new classes.