Use Case Diagram - Change Management

[sathish kumar]

Hi Guyss,

 

I have attached the Use Case diagram for Change Management. Let me know if I should any corrections

 

Regards,

Sathish

[karthic madanagopal]

Satish,

I think the extends arrow was misused in the diagram. Please see the information given below for more clarity.

When do I use the extends arrow?

The extends arrow (or extends edge) is drawn from a use case X to a use case Y to indicate that the process X is a special case behavior of the same type as the more general process Y. You would use this in situations where your system has a number of use cases (processes) that all have some subtasks in common, but each one has something different about it that makes it impossible for you to just lump them all together into the same use case.

Example: Suppose you wanted to add detail to the diagram shown below, representing an airline reservation system. Specifically, what you would like to show is that not all of the seats aboard the airplane are exactly alike (some window and some aisle seats), and sometimes passengers will express a preference for one of these types of seats but not the other. But of course, they cannot just be given their preference right away, because the seat they want might not be available. Therefore, the process of assigning a window seat involves checking for the availability of window seats, whereas the process of assigning an aisle seat involves checking for the availability of aisle seats. But even though these processes are different, they are quite similar in a number of other ways, so it doesn't make sense to ignore their similarities. Fortunately, UML lets us have both: we write that assigning these two types of seats are different processes, but they are similar in that both processes extend a common, more general process (assigning seats.)

When do I use the uses arrow?

The uses arrow (or uses edge as it would be called in traditional graph thoery) is drawn from a use case X to another use case Y to indicate that the process of doing X always involves doing Y at least once (although it may involve doing it many times, "at least once" is the only relationship guaranteed by this symbol.) This symbol can be referred to as an aggregation operator, because it indicates that a given use case is an aggregate (made up of parts) whose components are the use cases that it uses. If a certain use case uses several others, that means that all of the component use cases must be completed in the process of completing the aggregate use case, although there is no specification in UCDs of the order in which these are completed. A brief, mnemonic way to think about the uses arrow is that it it can be read X uses Y means that "X has a Y" as part of it's behavior.

Example: Suppose you wanted to add detail to the diagram shown below, representing an airline reservation system. First, you would create a separate diagram for the top-level services, and then you would add new use cases that make up the top-level ones. There is a uses edge from "Check in Passenger" to "Weigh Luggage" and from "Check in Passenger" to "Assign Seat"; this indicates that in order to Check in a Passenger, Luggage must be Weighed and a Seat must be Assigned. Similarly, the diagram indicates that in order to add a reservation to the system, the available space must be checked and the passenger's information must be recorded. You could imagine breaking these use cases down further to show more detail.

What is the difference between uses and extends?

Probably the best way to think about these diagram elements is as follows:

- "X uses Y" indicates that the task "X" has a subtask "Y"; that is, in the process of completing task "X", task "Y" will be completed at least once.

- "X extends Y" indecates that "X" is a task fo the same type as "Y", but "X" is a special, more specific case of doing "Y". That is, doing X is a lot like doing Y, but X has a few extra processes to it that go above and beyond the things that must be done in order to complete Y.

Regards,
Karthic Madanagopal

[sathish kumar]

Karthic, 

 

Actually in the slides given by Ron there are only two relations as include and extend. In the ppt u sent prabhu also it is the same way. Inclusion is the relation of bringing together similar object like the airline ticket example shown in the detail. But in the visio s/w there is no Inclusion option and it has uses, so i thought uses should come instead of Inclusion. But it seems its the other way around. I ll do the changes.

 

Thanks for correcting me.

 

Regards,

Sathish