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I have a not completed diagram of e-commerce order

I am not sure of the include and extend relatationship

Does this diagram is correct for the attached flow

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Christophe
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24sharon
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  • For your now deleted question https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/boolean-logical-operators#operator-precedence – Drag and Drop Dec 28 '20 at 15:17

1 Answers1

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About the relationships

An «extend» relationship E - - -> B means that E extends the behavior of B. B has a meaning on its own independently of its extensions, whereas E adds behavior in the context of B. E may be relevant on its own but it doesn't have to. According to your diagram:

  • Register extends Login. This would mean that Login is an independent use-case that provides value even without any extension. Conversely Register happens in the context of a Login and it could make sense on its own. I'd understand that the Login allows also to Register new users.

An «include» relationship B - - -> I means that B behavior always includes I behavior. B needs I, but I can is independent of B. According to your diagram:

  • Authentication includes Login. So Authentication requires Login
  • Create order includes Authentication. In consequence, every time an order is created, an authentication is performed, which requires a Login. Of course, this could make sense in a highly secured ordering system. But for normal business system, this would mean a lot of mandatory logins.
  • Search product includes View product. I'd understand that when a user performs a product search, the search results can be viewed, and one could navigate directly to the product view. But it's not clear which actor interacts with the search.

About use-cases

Use-cases should have value for the user and correspond to some user goals: Placing an order is certainly a goal for some users. But is the login really a user goal? Isn't it rather some detailed steps required to fulfil other goals? While UML is agnostic about the interaction that a use-case may represent (example argument in favor of a login use-case), use-case gurus usually consider this as a bad practice (example argument against login use-cases).

Use-cases should not be misused for functional decomposition. I'd therefore advise a careful review of the search and view use-cases: are these independent? Do they both provide value to the users? Or is one just a functional detail of the other?

Christophe
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