What are different characteristics of design classes in design engineering?

Analysis classes describes elements of problem domain. As design model evolves, some design classes are defined:
- refinement of analysis classes
- creating new design classes

There are five different types of design classes:
- Business domain classes.
- User Interface classes.
- Process classes.
- Persistent classes represents data stores.
- System classes.

For each design class, a set of attributes and operations are developed for each design class. Design classes present significantly more technical detail as a guide for implementation. The characteristics of a well formed design class are:

- Complete encapsulation of attributes and methods that exist for the class.
- The methods that are associated with design class should focus on accomplishing one service for the class. The class should not have any other way to accomplish the same thing.
- Collaboration is important between design classes but it should be controlled. Implementing, testing and maintenance becomes difficult if there is high coupling.
- Design classes should have high cohesion. It should have focused set of responsibilities and single mindedly applies attributes and methods to implement those responsibilities.
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