Can I mix use case and deployment UML diagrams?

Question

I am new to the world of UML and have so far learnt the basics of use case, activity and deployment UML diagrams. I have a requirement of where users interact with a system e.g. user sending an email, which is then processed by a system and then sent to an agent (person) who then responds and interacts once again with a system.

I am having a hard time picturing these requirements and whether it should be a combination of use case, activity or deployment. Can I intermingle them? What is standard practice?

Answer 1

As you know, use cases are used to capture requirements. When identifying and detailing use cases, you look at the problem from the perspective of users. Only focus on what an actor expects the system to do. First step is to identify the use cases and actors and then detail the use case flows.

1- Identify the use cases and actors

In your example send email could be a use case initiated by the end user (your actor). What happens next (e.g system sending a notification to the agent) could be modeled as part of the flow of this use case.

Another use case could be the agent actor handling what they have to do after receiving the notification from the system (a prerequisite of this use case could be that a notification has been received).

Note that you could combine these two use cases together and have the agent as a secondary actor (secondary actor interacts with the use case but does not initiate it). Whether you do this or not, is a modeler's choice and depends on the size of use cases, number of use cases and many other things.

2- Detail the use cases

After identifying use cases and actors, you should detail use cases. The most important part is to detail the use case flow (step by step interactions of actor and system). This can be written as text or drawn as an activity diagram.

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So to answer your question: yes it is possible and very common to combine activity diagrams and use cases; that is an activity diagram drawn to show the flow of steps of a use case.

Deployment diagrams on the other hand are totally irrelevant to the requirement elicitation phase. They model the physical structure of the system and how hardware components and software components interact.

In fact, it is very odd that you have learned component diagrams before class diagrams, sequence diagrams, state diagrams and many other diagrams.