UML Use Case diagram I created. Is my usage of include/extend correct?

Question

I just want to determine if I am using extend and include correctly. If I am using either incorrectly somewhere here please indicate where, and if possible, why it is incorrect.

https://imageshack.com/scaled/large/163/nlnk.jpg

Cheers.

Answer 1

Many relationships are clearly not correct here. However, I think the main issue with this diagram is not the correct use of include and extend, but rather to complex and overall unclear relationships. Although sitactically valid, you should avoid using more than one level of these relationships.

Your diagram is really hard to follow and to interpret.

Some refactoring ideas and corrections:

• show "Secure login" class separately, linked only with Actor and then apply the following precondition for all use cases that "include" it: "User is securelly logged in"
• "Logout after 5 mins" should be own use case, only connected to Actor as well, with 2 preconditions: "User is securelly logged in" and "User was inactive for 5 mins"
• Remove the include between "Logout after 5 mins" and "Initiate a call". Extend might be more appropriate
• reverse the direcction of the include between "Transfer funds..." and "Insure adequate funds..." - it is clear that the first one includes the second one and not vice versa
• consider breaking a diagram in 2 or more simple and small diagrams of only related UCs: all login/logout could for example be shown separate and simplify the view. You should not have more than 5-7 use cases on one diagram

Answer 2

I find this piece of advice before when I'm trying to distinguish the difference between using extend and intend in use case diagram.. I hope it helps you too. The original advice comes from this StackOverflow answer.

Difference between extend and include

Extend is used when a use case conditionally adds steps to another first class use case. For example, imagine "Withdraw Cash" is a use case of an ATM machine. "Assess Fee" would extend Withdraw Cash and describe the conditional "extension point" that is instantiated when the ATM user doesn't bank at the ATM's owning institution. Notice that the basic "Withdraw Cash" use case stands on its own, without the extension.

Include is used to extract use case fragments that are duplicated in multiple use cases. The included use case cannot stand alone and the original use case is not complete without the included one. This should be used sparingly an only in cases where the duplication is significant and exists by design (rather than by coincidence). For example, the flow of events that occurs at the beginning of every ATM use case (when the user puts in their ATM card, enters their PIN, and is shown the main menu) would be a good candidate for an include.

Also, from every book I've read, it is always recommended to use include and extend sparingly. Keep It Simple Silly.

Answer 3

It looks as though "secure login" is required to be performed prior to the other activities that you link with <<include>>. Include implies that the use case also runs the included use case every time which in this case is probably not what you intend (just one login per session). You can always create new stereotypes, such as <<precedes>> or <<requires>>. Using them consistently will allow you to convey your meaning.

Answer 4

Rules for using <<include>> and <<extend>> are simple:

• <<include>> defines a sub use-case which is always included in the general use-case: use-case -include--> sub use-case. Usually it's used to denote a distinct part of a use-case or a common part that can be reused by other use-cases.

• <<extend>> defines an optional sub use-case that can be executed upon certain conditions (which should be defined at a lower level design, not in use-case diagram). Here the direction of the relation is opposite to the <<include>> relation: use-case <--extend- sub use-case.

Apply these rules to your diagram and figure out if it's correct.