I've just read a book about UML and an currently trying to create a use case diagram of one simple domain.
The domain states:
There are two kinds of users: default and vip.
Default user can create no more than 10 posts.
Vip user has no restrictions.
What is the right way to bring this restriction into use case diagram?
Is my diagram correct?
If it's correct, can I model the same way the next statement?
User can give only one star to post
Thanks a lot for your attention!
It's almost correct. You should write the text in curly brackets. That will identify it to be a constraint. Further you should use the correct case for Default User. Eventually you can link the constraint to the actor as well. And yes, you can go on like that. Maybe, Rate Post is another use case. Think about that.
Related
I want to create a very basic sequence diagram for the first iteration of my app. I have a database of exercises, and I have a use case for creating, another for editing, and another for deleting an exercise. They are all very simple, and use the same elements and actors, like User, DAO, and Database. What I want to do is to create a single SD, that begins with the user asking to create an exercise, followed by the user asking to edit that exercise, and then asking to delete it. My question is: is this considered correct in a sequence diagram? I don't want to create 3 SDs almost identical to one another, and this seems like a simple way to represent all the information, but I don't know if this is correct by UML standards. Thanks.
From a standards conformance point of view, there is nothing in the UML standard, that imposes a relationship between your use case models and sequence diagramme models. So, no matter how many use cases you want to reflect in a sequence diagramme, it would be neither "correct" nor "incorrect".
From a personal point of view : What you are asking about is a question of modeling style, not conformity. As long as the people who are reading your models understand them, you can do whatever you want. So, something like this would be perfectly fine :
With this Use Case diagram, I'm unsure if I'm currently doing it correctly or not. Checked online and each site is giving me a different answer. I just need a direction or someone to correct me.
This is interesting as I am currently going through the exact same discussion with a client...
I would say "no" simply because I am unsure of what this actually represents.
A use case must bring a benefit to a user, and I really don't this in this diagram. What does Actor0 actually trying to accomplish? I do not get this from the diagram.
Did you write down statements before trying to do this? I find that going to a whiteboard and writing down what your actor's goal and how you see this happening so that the actor achieves the goal is a good start to better understanding the use case and differentiate the system being built from external systems. One way to do this is through a set of user stories (or use case slices).
And answering Thomas Kilian's excellent questions will also help you in this task!
Also, you are doing something that I see too often from people starting with use cases (and sometimes with UML experience): use case decomposition as a set of actions - basically trying to model a set of activities by breaking it down. Doing that is typically the second step in your analysis (e.g., by using activity and sequence diagrams).
No. Only "Register" (what?) and "Add/View Details" (which?) can be regarded as use cases since they add value. Neither "Login" nor "Main Menu" are use cases. The first is a constraint and the second an implementation detail.
I'm wondering if my use case diagram is about right and if anyone could give me some pointers if it's not.
It's for an application where users can login (always required). When they login they see a list with posts which they can up or downvote (like reddit). When selecting a post they can place and delete(only their own) comments.
The user that's logged in can place posts when logged in, but also has a button to view posts they've already placed where they can be edited and deleted.
Finally there's an admin that can delete inappropriate posts and comments.
Am I supposed to define that users can only edit and delete their own posts and comments? If so, how do I do that? Perhaps a different actor?
Thanks in advance!
There are a couple of flaws in your UCs.
Login is not a UC at all (it does not add any value to the actor). It is a constraint you may apply to UCs.
Wrong username/pw is no UC, of course. It's some message that will pop up somewhere.
Register is a UC on it's own. Connect it directly to User.
Using generalization with UC is not a good idea since it will bring in a lot of stuff for discussion. Leave it at the Manage level and describe inside the UC what this means.
<<include>> is usually used the wrong way (namely for functional decomposition). And you are doing that too. So leave it away, concentrate on the basic UC Manage comments and connect that directly with the actor.
If for some reason you need to describe some order for UCs you can use pre-conditions inside the UCs.
Remember that you cannot model everything using use case diagram. A single UC is a set of action flows that provide a specific business result. You can provide details on limitations (e.g. condition that you can manage only your own comments) in a description of UC (either modelled by activity or sequence diagram or simply in a written description) but not on UC diagram.
As the commenting is optional in your system, definitely you've used incorrect relationship. include means that the included UC will be always executed when executing including UC. In your case this is up to a decision of a user which means you should use extends instead (and of course in this case the relationship is in the opposite direction). See 18.1.3.2 (second paragraph) and 18.1.3.3 (first paragraph). You can also find confirmation of that in almost any book about UML based analysis (e.g. Howard Podeswa's "UML for the business analyst" to name one)
Besides that I agree with the list of flaws given by Thomas Kilian.
[Original Title] : Does an actor need to point directly in use case diagram?
or can I do it like this?
in this Use Case Diagram, I want to say that actor can use any use case in the pointed group-of-use-case.
does this kind of thing allowed?
Edit #1
The reason why I ask this question, is because when I create this use case there's a lot of line intersecting each other that makes me confuse.
And there's a comment :
It would be better to split that into smaller diagrams
does it mean like this?
Edit #2
after reading comment :
A UseCase specifies a set of actions performed by its subjects, which yields an observable result that is of value for one or more Actors or other stakeholders of each subject.
so I decided to change to this :
is this how a use case diagram should be?
Edit #3
CONCLUSION
An actor should point directly to use case
Read more the detail about how a Use Case Diagram should be in comment on this question
To be UML compliant you can not do that. But I guess one can understand what you are trying to communicate.
As a side note: Login is not a business use case. It is a constraint. Also with CRUD use cases I would not separate them but have a Maintain <object> instead (which itself is some borderline use case since maintaining something is not directly business relevant). You can constrain maintenance operations to certain actors separately.
Edit Regarding Login (one of my favorites): Use cases are most commonly used to describe business context (exactly as you are doing). So when looking from a business perspective, a Login is not a use case, but a simple constraint (you can do the business relevant things only when you are logged in).
Now for the Manage/Maintain use cases. They are on a similar level. Usually the "managing" itself is not directly business related. In many cases the focus on the real business was lost. So instead the reason why you manage something is the real use case (e.g. Correct User Data, Collect User Data). This is quite challenging and I confess that sometimes I also fall back to Manage. Most people don't bother but doing a good job requires to think over basics and not adopt bad habits.
On a Use Case diagram can you show things that an actor cannot do, for example because they won't have permissions to do it?
Or is it just implied due to the fact that they won't have a line joining them to the particular use case?
If the Use Case you are diagramming is the case where an actor attempts to do something that is not permitted and is then denied, then yes, I would show it.
Otherwise, I would stick to only including things that are actually part of the use case.
No. An Actor would be connected to everything that he can do. If the Actor can't do it, then it's not shown.
This is what alternate paths are for. The basic path (a.k.a. happy path) will show what happens when the correct Actor initiates the Use Case. In the alternate paths you can show what happens if the wrong Actor attempts to initiate it.
You might model Role actors that can do the task. You could then have another use case that has the original actor attempting to acquire the given Role.
IMHO this question and most of the answers give a wrong impression about the way use cases should be used.
Use case was intended as a requirements technique that uses natural language. It is most and quite effective that way.
It can be a thoroughly destructive technique when it is combined with too much UML/modeling. Structured modeling of use case texts for example by modeling main and alternative flows using UML Activity Diagrams is a tried and tested way for example to create Use Cases of Mass Destruction.
A use case diagram can be useful but we should remember the purpose of use case as a technique which is first and foremost to identify the user goals a system should support. Subsequently we can capture more details using natural language in use case texts using main flow, alternative flows etc.
Using diagramming tools we can visualize some simple information:
- For each user goal we can create model element type Use Case.
- Show system boundary using a box for the system with use case elements in it.
- Create a relationship between actor and use case to show the actor has a particular goal against the system.
Keeping an up-to-date list of actors mapped to goals is however of secondary importance. Doing a stakeholder analysis, drawing up lists of actors is a means to identify the users goals. After user goals have been identified it is strictly speaking not longer necessary to keep the lists of actors around.
If we are asking questions about how to put user permissions in a use case model we are most likely trying to capture too much information. We should abstract model elements away so that the model does not try to answer/capture these type of detailed design questions.