As you can see even a system as big as a vehicle sales system contains not more than 10 use cases!
for "Pay via Paypal", the condition would be payment_type=PAYPAL). Besides, there are associations that connect between actors and use cases.Often, people find it easiest to start the requirements elicitation process by identifying the actors. It is an international award-winning UML modeler, and yet it is easy-to-use, intuitive & completely free.These days use case modeling is often associated with UML, although it has been introduced before UML existed. UML remains independent of language and solution there.Isn't the Use Case stage far too early for such implementation specific concerns to be modelled? Achieving the right level of use case granularity eases communication between stakeholders and developers and improves project planning. Featured on Meta I hope you can answer "what is use case diagram" now and can apply use case in your project. If you want to link multiple payment transactions into a single logical payment, then extend the Make Payment use case, adding a "Process Multiple Payment Methods" use case or some such, which links multiple passes through Make Payment.Also, while I see the point now about possibly using extends to handle multiple payments, I still think that using the generalization model is more accurate. Enter discount code isn't.

Entering a discount code has to do with making a payment, but you don't have to enter one in order to make the payment. So you'd strive to capture that but remain open to different solution approaches.There are much more appropriate UML The child may add or override the behavior of the parent. You can look at the "is a" relationship to make the determination of which to use. Well, as indicated above, UML does not enforce any specific kind of implementation. Is there a hard and fast rule regarding which of the two to use and if so what is it?To my mind an extension is a weaker relationship than generalization as a direct substitution of the specialised use case for the base case The <> relationship is used to include common behavior from an included use case into a base use case in order to support the reuse of common behavior.The extend relationships are important because they show optional functionality or system behavior.
implementation is desired while extension implies some branching If "Pay via Paypal" were a specialization of "Make Payment" it would redefine the behavior of "Make Payment", which could be substantially different from the behavior of "Pay via credit card".Being an extending use case does not means that the alternatives have to be hardcoded. If yours contain more than 20 use cases, you are probably misusing use case diagram.The figure below shows the UML diagram hierarchy and the positioning of the UML Use Case Diagram.

Stack Overflow works best with JavaScript enabled Get Visual Paradigm Community Edition, a free UML software, and create your own Use Case Diagram with the free Use Case Diagram tool. There's an easy solution. Use case relationships are listed as the following:A Use Case diagram illustrates a set of use cases for a system, i.e. You can interpret a hint from the diagram for yourself, though. Using extends doesn't distinguish between single and multiple payment methods as clearly.Thanks @BobRodes I agree that generalization is the way to go, what I was looking for was a rule (of thumb) which indicates when one approach is more appropriate than the other. It does not show the detail of the use cases:As said, a use case diagram should be simple and contains only a few shapes. Indicates that an "Invalid Password" use case may include (subject to specified in the extension) the behavior specified by base use case "Login Account". If you want to learn more about other UML diagram types, please check the UML guide: You've learned what a Use Case Diagram is and how to draw a Use Case Diagram. It's something additional you can do while making a payment.Thanks for contributing an answer to Stack Overflow! UML Use Case Diagrams allow for two seemingly equivalent ways to show that a given use case might be realised in several different ways namely To my mind an extension is a weaker relationship than generalization as a direct substitution of the specialised use case for the base case must be possible in generalization but not necessarily in extensions.It seems to me that generalisation implies a polymorphic implementation is desired while extension implies some branching structure is to be used. Visual Paradigm Community Edition is a UML software that supports all UML diagram types. As you indicated yourself.When modelling with an extend relationship, the extending use case (pay via xxx) is executed when the extended use case (make payment) is at a precise location (given by the extension point, payment type) if the condition for such extend relationship holds (e.g. ; Depict with a directed arrow having a dotted line. Use Case Relationship Visual Representation; Extends. They aren't associated with one UC diagram or another. The following questions can be asked to identify use cases, once your actors have been identified (Schneider and Winters - 1998):Now, check the tips below to see how to apply use case effectively in your software project.Use case granularity refers to the way in which information is organized within use case specifications, and to some extent, the level of detail at which they are written. The Overflow Blog A use case diagram consists of the system, the related use cases and actors and relates these to each other to… Where developers & technologists share private knowledge with coworkersProgramming & related technical career opportunitiesBoth implementations model the same problem.