Association between two use cases in UML

Question

I know that two use cases can be associated together with the following relationships,
1. extend 2. include 3. require
Apart from these relationships, is there another way to associate two use cases?

http://www.visualusecase.com/visual-use-case-screenshots/use-case-diagram-editor-screenshot.html

If someone could tell me whether the association between rent video and charge credit card use cases is legal or not? I am not asking about the include relationship, it is about the one without a name.

Answer 1

First let's give right name to this relationships:

In Use Case Diagram, between use cases, you can define 3 relationships:

1. Include
2. Extend
3. Generalization

Then Warn You About Use Cases

Use Cases are text stories which shows interaction of "actors" with system in order to reach a "goal".

So instead of asking "is it okay to use use this relationship or not, first write your use case scenarios. You do not have to ( and should not) write all of them in details. Work in an iterative way.

Check The Life Cycle of a Use Case

Include RelationShip

While you are writing use cases, if you see that some steps in use case scenarios , occur again and again.[ many times] then extract repeating steps a separate use-case, then reference it from the other use cases using "include" relationship. [to avoid repetition]

Or you may use "include" relationship to decompose a long use case into smaller sub units. [Be careful, avoid functional decomposition]

Extend Relationship

You have an optional behavior in use case base based on a condition. But many times, while you are writing your use cases, you have a Extensions sections and without showing extend relationship in a diagram, you can just record-write optional behavior in that [Extensions] sections. But if you think optional behavior is important and should be seen on use case diagram, then show it on diagram with extend relationship

Generalize Relationship

If you are a novice modeller stay away from Generalize Relationship. It is interpretation [ how to write its text story ] is somehow problematic. If wanted to get more info Check Chapter Using Generalization between Use Cases of the book Use Case Modeling,Kurt Bittner Ian Spence or Patterns for Effective Use Cases , Steve Adolph, etc... [ Section 7.5. CapturedAbstraction—A Pattern for Applying UML Generalization, by Dan Rawsthorne]

About Sample Diagram:

The "Rent video" and "Charge credit" card relationship is technically legal since it is said that Rent Video use case include "Charge Credit" : In order to rent a video you should always charge credit card. And this step[Charge Credit] is also repeating by Pay Late Fee use case. [according to your diagram]

And discount is "optional" based on a condition [may be if you take more than 3 you have] so "extend" is also technically legal.

But you have unnecessary lines , which I do not understand.

Final Advice:

Do not waste your time on Use Case Diagrams to much.The important thing is use case scenarios. And when possible use minimum relationships in your use case diagrams.