CODEWITHSUNDEEP
umlclass-diagramecb-pattern
Ju Ju
Ju Ju

Reputation: 199

What is the use of control classes?

I am trying to understand how to classify the classes as boundary/control/entity classes. I can understand boundary and entity classes although my understanding may not beperfect. Boundary is the classes which interacts with the user. So the classes used for the userinterface will be boundary classes. Entity class handles data. So entities I use in the ER diagram will be entity classes. But I understand nothing why control object is used. It is said that control object is used to encapsulate domain functionalities. What if the control classes are not used. Can you please explain me with example.I found some explaination but I am still confused.Why boundary should not interact directly with entity? There are also classes which are not boundary/control/entity. What are they?

Upvotes: 3

Views: 3899

Answers (3)

Christophe
Christophe

Reputation: 73386

Background

The Entity/Boundary/Control approach was introduced by Ivar Jacobson in 1992 as part of his use case driven Objectory development method.

At that time Jacobson used the terminology Entity/Interface/Control. The strange circle notation that you can find in relaction with ECB was already used in his books in 1992 and in 1994. By the way, the use case of his methods were integrated into UML and his development process was merged into RUP, when Rational acquired Objectory.

The idea behind his method was to adopt a very logic and formal and deductive analysis and design approach. It starts with identifying the systems behavioral requirement with use cases. Each link of use case to the outside world would then be represented as an interface object responsible for encapsulating completely the user interface.

Each use case would be represented as one or several control objects:

Control object: An object that encapsulates functionality of one or several use cases - I.Jacobson in The Object Advantage, ACM Press, 1994

Finally the business objects managed by the system can be partly inferred from the use cases, and during the analysis.

Additional information

The fundaments of the Iconix process were introduced in 1999 as part of the book "Use Case Driven Object Modeling with UML" by Rosenberg & Stephen. Some additional robustness constraints were introduced, certainly to improve separation of concerns. For example, the direct link between entity and boundary is prohibited. Everything has to be channelled through control objects:

Control objects (which we usually call controllers because they often aren't real objects), serve as the "glue" between boundary objects and entity objects - D.Rosenberg, in the linked DDJ article.

They add a recommendation to clarify the intent :

Both boundary objects and entity objects are nouns, and controllers are verbs.

Conclusion

So the principle is that the control object represents the business logic offered by use cases, interacting on one side with the boundaries, and on the other side with the entities. Control objects can't be invoked/accessed directly by the outside world.

If you would want to avoid the control objects, you would have a boundary objects with methods corresponding to the verbs/functions/use-cases that your system is supposed to provide. This wouldn't be according to the modern ECB, but perfectly valid according to Jacobson's original approach. Nevertheless your boundary would no longer comply with the single responsibility principle of a SOLID design.

Upvotes: 1

qwerty_so
qwerty_so

Reputation: 36313

The control classes contain the business logic. It's the most important part of a system. While the boundary just controls whether the text is green or blue (very basically) and the entities control whether data is stored in text files or databases (also very basically) the control classes do all the business logic. What to change in the entity when the boundary send mouse/keyboard events an vice verse what to show from the entities in the boundary.

Upvotes: 0

Daniel Rodriguez
Daniel Rodriguez

Reputation: 617

  • Boundary interact with actors (e.g. users).

  • Entity classes represent data.

  • Control mediates between the boundary and the entities (e.g. executes an operation on the entities)

Source: http://www.cs.sjsu.edu/~pearce/modules/patterns/enterprise/ecb/ecb.htm

Upvotes: 0

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