I have a specific question about this conversion. I saw different examples and I am confused at this point: Do I have to draw all classes in class diagram while drawing sequence diagram?
No, you don't have to do that. A class diagram shows a static view of a system. And it only shows that part of the system which is relevant. Only very small systems go into a single diagram. For large systems you create multiple sub-domains you can represent in a single diagram. Wall papers are more or less just for the show.
A sequence diagram in contrast shows actual behavior of the system. And again a SD will not show the complete behavior of the system. That even more than class diagrams since behavior is exponentially more complex than anything static. So for a SD you will highlight only a certain part of behavior where only certain classes of the system take part in the communication. And even then you are allowed to leave away parts of the communication if they are not really relevant for what you want to show. A SD is created to highlight only some part of the behavior. In that respect you create as many SDs as needed.
As commented, what you put in a SD are lifelines which represent instances of a class, not the class itself.
Related
The picture is taken from the book "UML # Classroom". The text says "the registration is via e-mail, that is, asynchronous".
In actuality, I believe, there would be no "Student" and "Professor" objects involved in the process. Rather an interface, a call to a mail server and in general, nothing that would tell the viewer of the diagram what is really going on.
That makes sense to me because it has an illustrative purpose. The methods of the classes in the sequence diagram would only resemble the methods in a class diagram at a low level.
If I am tasked with a high level view of class diagram and high level sequence diagrams of a particular interaction, if I am then asked why the classes of the class diagram don't have any of the methods of the sequence diagram, am I right to say that they simply don't have to?
Should I reach a compromise with the sequence diagram wherein I try to make the calls similar to what will be going on in the program?
The methods of the classes in the sequence diagram would only resemble the methods in a class diagram at a low level.
Not necessary, all depends on the goal of the sequence diagram, you can have classes at design level (may be allowing to generate code) but having them in a sequence diagram giving a semantic (high) level. You can also show these classes in class/package/... diagrams without low detail so not at design level.
The only rule is to have diagram saying something useful, and following UML specification of course. Do not forget UML is not a method but a language, it does not indicate how it must be used.
Remark you can put note in a diagram to help saying explicitly its level/goal in case you are afraid it is confusing because not 100% limited/dedicated to design even using classes part of the design.
if I am then asked why the classes of the class diagram don't have any of the methods of the sequence diagram, am I right to say that they simply don't have to?
yes, because the goal is not necessary to show a sequence of calls but for instance a higher level.
Should I reach a compromise with the sequence diagram wherein I try to make the calls similar to what will be going on in the program?
Of course you can do too.
Notice a sequence diagram (so in fact an interaction) has limited features, while for instance an activity allows to model a behavior in detail without the same limitations.
I would like to make a component diagram for a multiple robot coordination system.
I would like to show on the component diagram that the sub-component "Perception" of each "Robot" component communicates through an interface with each other. Indeed, the sensors of all robots are used in order to estimate the position/velocity of each robot, it is a cooperative sensing.
How can I do that ? Should I have an interface which would be both provided and required by the component "Robot" ?
Thanks.
For this type of system you are in position to use full power of UML and make really effective documentation. You will most likely need some (or all) of the following diagrams:
Component diagram - to show the "big picture" and the main parts of your system ant their interfaces and dependencies. Components are "black boxes" here and will be detailed in the following diagram
Composite structure - are perfect to open up the components and show their internal structure. You can take "black boxes" and their interfaces as kind of input to this work. Each component (except the external ones) should be modelled internally. This kind of diagrams lets you use the whole-part paradigm to model internal structure as a network of interconnected elements. Previously detected interfaces will be used here to show how they are actually implemented.
Class diagrams. If you need to further specify the elements of internal structure (their attributes, methods, associations, etc), this is the diagram to draw.
State machines. In embedded real-time systems, lots of classes are active and have states. Identify those classes (or even components) and use state diagrams to show their internal logic.
Sequences and interactions. These diagrams will help you to specify how different elements of your system work together to implement different scenarios.
Deployment diagram. As robot is a piece of hardware and these components run on it (or them, if there are more than one hardware node) you might want to show how the components are distributed over the hardware structure.
You could also have a look on timing diagram, relativelly new one, designed especially for real-time systems. It might come on handy if you need to express time restrictions, durations, etc.
If you are new to UML, I would recommend to start with components and deployment. They are relativelly easy to learn. As you feel understanding and need to express your ideas further, dive in the composite structure and states. And finally classes.
Have fun!
EXAMPLE
This is how I understand your model and its elements. This extends my comments.
Explanations are in comments and in the diagram notes.
A component diagram:
A component instances' diagram:
Note that the first diagram should be extended with the "connectivity rules" that define all valid connectivity possibilities. Is there only one CentralManager? Must each Robot be connected to CentralManager? Can a Robot talk to itself? And so on...
These and other questions should be modelled separatelly. On class diagrams benavior diagams, according to concrete details.
I have a equipment which I am representing with a class and there are two actors a remote and local operator who can put the equipment on or off. Both actors will use the functionality of the equipment. But How do I now represent them using sequence diagram, since if I draw an event from both local and remote its going to show at the equipment the one happened after the other but in reality two actors are using the same function and can invoke it any time. So how do I represent the two actors in the below sequence diagram.
P.S. The RAN40L is the equipment and CMS is remote operator and Simulator Operator is the local operator.
As it happens I have extensive experience from the defence industry, including naval CMS, so I am familiar with the domain.
The crucial question is, as always with UML, what you want to show in the diagram, which of course ties in with what you are showing in other diagrams. No diagram is ever read in isolation and you will never capture the entire radar functionality in a single sequence diagram.
Remember that a sequence diagram is intended to show things happening in a strict sequence. It is possible to show some rudimentary concurrency using the appropriate fragment, but if you want to show that the two actors do exactly the same thing, that the sequence is in fact one and the same in both cases, then the sequence diagram is the wrong place to show that.
Assuming that this sequence is intended as an elaboration of a use case, then the solution is to replace the two actors with a single actor, eg "Radar Controller". This actor can then be specialized into CMS and Simulator, which makes sense if the radar is unaware of, or unconcerned with, who is interacting with it in some (use) cases but not in others.
If the radar never makes the distinction, there shouldn't be two actors at all. The actors must make sense to the system they're interacting with, otherwise there's something wrong with your actor model.
So one solution is to structure the use cases as below.
http://sdedit.sourceforge.net/images/webserver.png
This is a good example where two actors are used. It is default to put one actor to the opposite the other (this is not done in the example).
Actor is considered to be just another object in the sequence diagram. You can plase arbitrarily many actors and use them just like any other object, no restrictions in this sense.
There are some stylistic guidelines though, most of all regarding Actors positioning on the diagram. It is a common practice to show the actores on the border of the diagram, keeping internal system objects inside. Moreover, human actors are typically shown on the left side, while system actors are kept on the right. Actors should not be "mixed" with system objects. Here is a simple example:
Everything in behavioral diagram is executed after behavior defined by diagram started.
If actors interacts individually, and their interaction are not moxed in single execution, you must draw diagram for each case.
I would say you need two diagrams, each for one actor.
I would like to know which diagram from those two should be created first when designing large IT system.
In every article I read about UML, the component diagram is mentioned as almost last.
I think that, when designing a larger system is better to divide it to smaller parts/modules on the component diagram and then for every component create a detailed class diagram. Is that correct?
How it look in practice from your experiences?
Do you know of any article/tutorial that shows from beginning to end, the design of system using UML?
There is no mandatory order for UML diagram design - in fact, you will often find yourself creating several simple diagrams of different types, and refining them later. The process is generally iterative but doesn't have a follow a particular order.
That being said, some UML diagrams provide a more abstract view than others, and it may sometimes make sense to start with the most abstract views and work your way down to the most specialised ones. Use case diagrams typically come early, while object diagrams or state diagrams often come later in the design process, once the original, abstract solution has been refined.
You will also want to take a look at consistency between your diagrams: indeed, with several views you will introduce redundant elements, and it is important to make sure that they do not contradict each other. For example, if you have a sequence diagram and a class diagram, any call message in the former should correspond to an operation in the latter. See Alexander Egyed et al's work for automated consistency management and correction in UML models.
I've had this discussion with my professor at college about UML diagrams .
He believes that sequence diagrams should be drawn before getting to class diagrams, but I think the opposite . I think after finishing the usecase diagram , the next diagram should be class diagram and after that we should get to sequence diagram.
Rational rose requires us to use the classes in sequence diagram, which are already in class diagram.
Can anyone help me with this?
I think you're both wrong. They should be drawn at the same time. As you're drawing your sequence diagram, you will undoubtedly come up with properties that you will need to keep track of the state, or that you hadn't thought of if you do the class diagram in a vacuum.
Of course, this is highly subjective and personal, but years of real-world experience (as opposed to academic theory) have taught me to work on both at the same time. MAYBE starting with the class diagram, but the class diagram invariably changes when you start going through process flows.
Well it depends a lot on how you plan to do things. I think it's a subjective matter. If you rather explain the actions performed for your usecases and after this has been done write the classes based on what you need to perform the sequences your professor is right.
But if you prefer to determine what the structure of your classes are and then adapt the action sequence to this then you would do the class diagram first and later the sequence.
In my experience I do them concurrently. I put the fundamental attributes to the class diagram but not the actions, and while I do the sequence diagram I add the methods and attributes that I need to the class diagram.
There is no one standard answer. There are several opinions, approaches and methods. In Unified Process I believe you first identify use case and then make realizations for them, e.g. sequence diagrams. As in use cases, there are actors and the systems and/or its parts interacting ina sequence. Actually this interactions should help you decompose your design and get to classes. Once you have classes on the analysis level, you can go further to design classess and design interactions. However these are quite a lot to draw in a diagram, most of the times code is the best documentation on this level, even generated diagrams are too large and more difficult to understand then code itself.
To prepare sequence diagram you need classes not the class diagram
You can prepare empty classes on the fly while in process of preparing sequence diagram....
Identification class objects in be part of preparing sequence or you can try to identify your objects before hand....
sequence is logical process while class diagram is end output
I don't think there is an order for creating diagrams since both are two different views of a system: class diagram structural (static) and sequence is behavioral (dynamic). I would start with sequence diagrams since you will discover more classes to create as you go through sequences. Do whatever makes sense for you at the time. If your doing more object oriented programming, I would consider doing classes before sequences.
Structural and behavioural models for all but the very simplest systems are naturally created simultaneously and iteratively, refining both over time.
You may have some method of "object discovery" such as CRC cards, which will yield a set of initial classes, with collaborations (the classes they interact with) and responsibilities, which informs both the methods they will need, and internal behaviour/state/activity.
You may then want to explore the use cases and scenarios using sequence or communication diagrams, this will expose the details of the required object communication and therefore inform the generation of public methods and relationships to refine the class diagram while at the same exploring the system behaviour which may yield further objects and classes to be created.
You may also want to explore the internal behaviour of classes, especially if they have stateful and/or active behaviour; activity ans state-machine diagrams are useful for this.
Either way I doubt that the use of Rational Rose is really the determinant of diagram creation order. Rational may require the classes on a sequence diagram to exist, but I imagine that they need not actually appear on a class diagram; they can probably equally be created on the sequence diagram and then later placed on a class diagram, or even created in the project explorer or whatever the equivalent is in that tool. Even if the only method of creating a class is to place it on a class diagram, that does not require you to refine and complete the class or its relationships before exploring interactions on a sequence diagram.
You need to buy some clothes, how you will proceed. You start choosing clothes first or you will decide first where to go? At the same time, will you go to shoe store if you want to buy shirt.
So both are iterative, but definitely first step is sequence on very high (component) level then drill down to class level sequence
You should first decide your application flow,means you should first draw a sequence diagram. It will show the flow of your application after this you should go for class diagram.