In my UML Use Case diagram I've got 1 actor(User) and 2 use-cases(Login and Registration). They are connected as in image below(Association between User and Login, and Extend between Login and Registration)
I've read on online sources about UML about the relationships in the use-case diagrams, but I have problem in defining Registration use-case. In which situations can Registration use-case be optional and mandatory?
P.S. Feel free to advise modifications to this diagram.
A use case shows an added value the system under consideration delivers to one of its actors. With that respect, Login is no use case at all, since it does not deliver added value. Rather, it is a constraint you can apply to use cases.
Registration is not a good naming for a UC. You should stick to predicate/subject[/object]. So Register for <missing since you did not mention it> is a good name for that UC. And, now that it is a singular UC, you see that it does not extend anything. The use of extend/include is anyway in most cases a sign of functional decomposition. And UCs are not decomposed as added value is a singularity that can not be divided. Remember the caveat: If your UC diagram looks like a spider web, your design is broken (you tried functional decomposition).
I always recommend to read Bittner/Spence to get a good understanding of synthesizing UCs.
Addendum: I said that Login is no use case. And that should be true in general. UCs are usually used in a business environment. However, if you also model UCs in the technical environment, you can have Login as UC. But UCs in a technical sense are a bit awkward. I always recommend to stay on business level with UCs. I think that's more stringent. In a technical environment you do have other means of describing things.
Related
I've never made a use-case diagram before so I'm wondering if mine is correct or not.
In short
This is an (almost) valid use-case diagram. But this does not make make them good use-cases. But what matters in the end is if it is useful to you.
More details
Is it formally correct according to UML?
UML is value-agnostic and defines UC on page 637 of the specs (highlight by me):
A UseCase is a kind of BehavioredClassifier that represents a
declaration of a set of offered Behaviors. Each UseCase specifies some
behavior that a subject can perform in collaboration with one or more
Actors. UseCases define the offered Behaviors of the subject without
reference to its internal structure. These Behaviors, involving
interactions between the Actors and the subject, may result in changes
to the state of the subject and communications with its environment.
Let's check the validity of your UC in view of this definition:
Start game, move paddle, restart game, and exit game are behaviors that the game (subject) offers in collaboration with the player (actor). These are valid UC according to UML.
Ball falls, hit all bricks, hit brick, and display score are behaviors that are more questionable: they do not require a collaboration or an interaction with the player. You could nevertheless argue that these make sense only if the user observe these behaviors, so there is an interaction with the player. So it could be claimed that these are also valid UC in regard of the UML definition.
Add score seems to be a purely internal behavior that is done without the user and not even observed by the user. This would not be a valid UC. However labels might be misleading: if Display score would mean the final game-over score and Add score would mean an update of the score on the screen, it could again be argued that it's a valid UC.
The use of extension (optional) and inclusion (systematic) seem also correct.
Is it a good UC?
While UML is value-agnostic, many authors define a use-case in a more ambitiuous way. In particular Ivar Jacobson, the inventor of the Use case defines it as:
A use case is all the ways of using a system to achieve a particular
goal for a particular user. Taken together the set of all the use
cases gives you all of the useful ways to use the system, and
illustrates the value that it will provide.
According to this definition, there is only one single use case here:
Play a game : this is the goal of the user that brings him/her value.
All the other elements are only ways of using the system to achieve this goal. So they belong to the single use-case. A approach would be to represent them as detail of the use-case description:
One suitable way would be to show these in terms of intent in an essential use-case. This approach was invented by Constantine and Lockwood in 1999. It is used centered and leaves full flexibility about the sequence of actions in the user interface.
Another modern way is the Use-Case 2.0, invented by Ivar Jacobson in 2011. These detailes would be shown as use-case slices, in a very similar way than user-stories.
I've recently been learning about UML use case diagrams and I have a few minor questions about this UML case diagram that I have created.
Does view schedule <<extend>> from create schedule?
If yes, then does this work properly by including the Login?
Is it necessary to <<include>> username/password for the login or should I simply have "Login" without username/pass
p.s. I know this is very basic but i'm unsure about whether or not I've got the hang of this.
Thanks.
There are a couple of issues.
The <<include>> is meant to include UCs, not objects. Since Vehicles/Drivers/... are not UCs that's wrong.
The fact that Create schedule extends View schedule seems odd. To me both are individual and independent UCs.
Finally Login is no (business) UC. It is a constraint which is to be applied to View schedule. Attach a <<invariant>> {must be logged on} to the connector to User
Remember: a UC is about added value for an actor. That's what the UC is named after. For that reason Login is no UC (but a constraint). Avoid include/extend since it is a sign of using functional decomposition. UC is about the opposite: synthesizing work steps that belong to a single added value.
I have heard conflicting things about this and just wanted to clarify.
I have always thought that when constructing a Use Case Diagram, I only include the activities that will be carried out by the system. For example, if it were a bank atm, "User depositing money" would be included, as it involved the user interacting with the atm. However, "User is paid cash in hand from job" is not included in the diagram, even though it may bear relevance to a scenario or situation.
Thanks all
The fact that the user is paid in cash is in any way related to the information system which is a system involving people. The payment transaction has to be integrated with your project, at least on a conceptual point of view. In other words it should have a relationship of an unspecified kind with a use case, depending on the context.
I recognize my answer is quite messy: if you're already getting bored, jump directly to the solution section...
The use cases diagram
According to The UML User Guide:
A use case is a description of sequences of actions that a system performs that yield observable results to a particular actor.
The point is about modeling what is related to the system: your main problem is to consider the scope of your project.
Depending on the scope you identify, the use case you should consider would be something like Cash withdrawal: consider the observable results from the point of view of the actor. This part is highly subjective whether you consider the operation part of the system or not. I personally disagree with the other answers here.
A few words about being paid cash in hand. On a pure development process point of view, would it be normal to have a sharp idea how a user is being paid while modeling ? Still the scope question here: perhaps is it a strong constraint in your context.
Even when reverse-engineering, a use case is user-oriented, it has nothing to do with how things are done, but what is done: I think nothing to do with especially automating things, even when talking about a system. There is a subtle idea here: I consider an information system, a system involving people in the first place, not a completely automated system. Of course, purely automated systems can be modeled with UML, but most systems involve users.
The relationship between the use case itself and the information how the payment is done has not to be represented on the diagram figure. However, even if this is not in the use cases spirit, the way it is done could be written in a note if it is an important constraint the diagram reader should be informed of.
The solution
In my point of view, the right place to put that information in the use cases is not the diagram figure itself but in a use case description. Martin Fowler gives a few hints about this in UML distilled. You have a simple use case description example here. This is related to the way you are using UML and the way you wish to describe use cases (I personally share Martin Fowler's perception).
Perhaps you would prefer to represent this with a formalism specific to your modeling software, but I think this would not be a traditional way of using UML (appropriate for an Executable UML, not appropriate with blueprint or sketch).
It is not included because the "User is paid cash in hand from job" is outside the scope of a project and would not be needed for what you are trying to create.
Most often use cases are used at the functional/logical level of your model (MDA's PIM level). This means that it only describes those parts of the process that will be automated.
So unless your system has a feature that somehow records the fact that the user is paid in cash, that isn't part of the system under construction.
At the business/conceptual (MDA's CIM level) level however you model the whole processes, regardless of automation. So at this level it "User is paid in cash from job" would certainly be at its place.
In an use case I have two Actor/user:
Patient
Expert
Both of them can do create/view/edit on patient profile. Expert can do them on all profiles,but patient can effect only on him/her profile.
I have to keep diagram clear and avoid from repeating the same things. Now I want to know is there a way to draw create/view/edit once but describe patient's limitations? Or it may be my mistake and it is better to use another diagram to describe limitations of actors? Sorry,but I am new by UML.
In the UML Use Case diagram there is (as far as I know) no built-in way to visually capture constraints. You can show then using the invaluable note symbol:
Although you can model the access right policies using some simple means:
realistic user access rights management will be probably implemented using access tokens, authentication, authorization and all this stuff delegated to another (complex and reliable) system component providing some kind of CanAccess(who, what, CRUD): boolean service to the "system".
In order to capture the various limitations you would typically put them into the precondition part of the Wikipedia: Use case narrative.
In the UML model the limitations would map to constraints and guard conditions shown in the behavior diagrams describing the use case.
See also:
chapter "Describing Use Case Behaviors" in uml-diagrams.org: UML Use Case
A use case diagram is not meant to show the permissions that each actor has to perform particular operations. It is meant to show what the system has to do and who it has to do it for.
In this case, I'd say you have only one kind of actor for this use case diagram: User. And you have the use cases: "User Creates/views/edits".
The exception would be if the Create operation of an Expert is different from that of a Patient (in a way that would be visible on the use case diagram). For instance, if "Expert Creates" also has to perform "Expert Sends Email", then that would be a reason to consider two separate actors.
Does anyone know how to describe (specify) the use-case that includes another usecase in the use-case specification table?
For example, I have a use-case "change password" that includes use-case "login" (this is just an example, i know that login should just be in the pre-condition of the use-case)
May i specify it like this?
Use-case identity: Change password
Actor: User
Pre-condition: ...
Normal flow:
Do use-case "Login"
....
....
....
What is the proper way to specify the use-case that includes another use-case?
It depends on the further rules and conventions used together with the "use-case specification table" document. Consult your company documents for the rules (and some examples).
Overall yes, your approach is valid.
The "Login" use case might be also invoked implicitly if you'd move it to the "Pre-condition: User is logged-in"
Even for free text without any Software Requirements Management tool consider using the "Name and unique-number" referencing best practice
To wrap your head around it I'd recommend (among other Google-able resources) to read the Alistair Cockburn's book "Writing Effective Use Cases", draft version is available online on his site - http://alistair.cockburn.us/get/2465
EDIT: after #BobRodes's challenge to share some alternative methodology
For more serious work consider using a Requirements Management tool, or at least evaluate some tools to adopt the best practices they support/recommend.
For one example see the link below explaining how Sparx Systems Enterprise Architect formalizes work with Use Cases and how Use Case traceability works and how it can generate documentation, UML Activity Diagram etc.
Sparx Systems: Model-Driven Use Case Analysis with Structured Scenarios, Webinar August 2013, 18min video
For another example of managing Use Case traceability and what usually happens after the Use Cases are written see
Jama Software: Jama Recorded Demo, 30min video
You might want to look into "use case narrative". In such a narrative, one of the things you will do is list included use cases and extension points. So, add a section called "Includes:" to your narrative, before the normal flow section.
Edit: Here's a bit more from Tom Pender's "The UML Bible":
The features of a use case narrative aren't standardized, but these
are common elements in wide use:
Use case initiation, or trigger, describes how to start a use case.
Assumptions define conditions that must be true before the use case may execute, but are not tested by the use case.
Preconditions define conditions that must be true before the use case may execute, and are tested by the use case.
The use case dialog explains how the user (whether an actor or another use case) interacts with the system during the execution of
the use case.
Use case terminations define the different mechanisms that can cause the use case to stop execution.
Post conditions define the state of the system that must be true when the use case ends. This helps prevent use cases from leaving
the system in an unstable condition for other use cases that follow.
Minimum guarantees describe what the actors can expect from a use case, no matter what happens during the execution of the use case.
Successful guarantees describe what the actors can expect from a use case when it completes successfully.
Although these elements are valuable, they are by no means exclusive.
Definitely look into other books and online resources on use cases,
and augment the narrative to support your own method of development.
So, perhaps I shouldn't have said that you "will" list included use cases and extension points, instead saying that you "may" do so. I like to put them in, so I don't have to keep referring back to the diagrams to look them up. Of course, you can just mention them in the dialog, too.
In UML there is standard relationship named include. Start relationship from including UseCase and end on included UseCase. See UseCase section of UML Superstructure document. UML website