According to UML context diagram context diagram doesn't exists.
So my question is which one of UML diagrams is good to show something like this and how to paint this?
I've just found the following definition: http://en.wikipedia.org/wiki/System_context_diagram
That's probably what you need. :)
A context diagram defines a boundary between the system, or part of a system, and its
environment, showing the entities that interact with it.
There is no single diagram in UML that would map to this definition, but I have some good news - there are several diagrams (out of total of 14) that can show the frontier between the system and its surrounding world from different perspectives. This is much more flexible than only a context diagram.
First of all, I would mention a special UML element - a boundary. It can be used in any diagram type to show some kind of delimitation. You might want to optionally use it to visually delimit between the system and its environment, especially in situations when this is not explicit.
The following diagrams can show the boundary between the system and its environment:
Use case diagram (your example) support the context explicitly on the functional level. Use cases are elements of the system under development, while the actors are extern entities (systems or human users). Before mentioned boundary is often used to visually delimit between the system and its environment.
Component diagram is used to model some kind of software modules (applications, DBs, external systems, libraries, etc). You can use it to show both internal and external components and the way they interact. A boundary can be used to clearly draw the separation line.
Activity diagram can show your system/business/usage processes. Some activities can be performed internally, others externally. Here you don't need the boundary, but the so called swimlanes to depict who does what.
Sequence/collaboration diagrams are another option. They show the communication sequences between several objects. If you split those objects in internal and external ones and wrap them up with the boundaries, there is another context diagram. :)
UML is flexible, there are probably further options, but I think this is enough to get the idea.
Names of your association are services. UseCase in center of diagram is context of services definition. See usecase diagram:
It could be done with a use case
http://en.wikipedia.org/wiki/Use_case
EDIT:
Reconsidering it, use case diagram should be the next step once the operations are defined so first you shouls make a system sequence diagram.
http://en.wikipedia.org/wiki/System_sequence_diagram
If you're happy with going into the not complete superset of UML that is SysML, you can have proper Context diagrams there.
However, context diagrams in SysML are simply Block Diagrams showing system context… and Block Diagrams happen to be the same as UML2 Class diagram, where the classes are of stereotype «SysML::Block».
So you can define your context diagram in terms of aggregation of blocks to your system, with the relevant stereotypes, basing it on UML2 Class diagrams.
I tend to use collaboration diagrams for this. So for each major scenario of each use case, draw a collaboration diagram showing the actors, with the application as a single entity in the middle, and messages travelling around that show how the application interacts with the actors in order to fulfil the scenario.
(I don't put too much detail in the messages -- I only want to show that there is a delegation of responsibility and some kind of interaction, but I don't care about details of actual messages, views, data etc.)
I find the context diagram does have a particular appeal. It sits well with business users, showing them the scope & parties of a system in a very easy way. So, I tend to create a context diagram, even in contexts where UML is prevalent.
Related
I discuss with my friend our project and we are in a way to draw the sequence diagram ( UML 2).
He told me that the sequence diagram is drawn by the use case. It means that for each use case we should draw a Sequence Diagram.
Is it correct ?
Thank you for any suggestion.
Well, taken as dogma it is not correct. A sequence diagram (SD) shows the behavior of objects in the way they interchange messages (and also if needed their lifetime and some minor additional information). You "can" also use a sequence diagram to describe scenarios in use cases. But simply speaking, a SD is more technically oriented (class design/programmers) rather than business (business design/stakeholders). To visualize a use case scenario you're better off using activity diagrams (AD). And even better if you dive into BPMN (which brings ADs to a new level).
It is possible though, to convert ADs to SDs and vice versa without information loss (if you forget about the afore mentioned bits and pieces).
Now another point: you will not necessarily need a diagram for each use case. I found that often use cases are more easily (and even clearly) described in a textual way (see Cockburn or Bittner/Spence) rather than diagrammatically. Especially if you have UC scenarios that are very linear in their single actions. So you can leave out the AD for those and just fall back to simple text. You should further avoid describing UC scenarios in both ways (i.e. text and diagram) as this introduces unwanted redundancy (means you would need to maintain always both when changes happen; and they happen often; and people are lazy -> so which one holds the truth: text or diagram?).
Generally, as Thomas points out, use case detail is set forth in an activity diagram. As he also mentions, a use case scenario would use a sequence diagram, when necessary. A use case scenario is a single path through a use case.
Sequence diagrams aren't good at diagramming multiple simultaneous behaviors and multiple decision points, and use cases generally have both of these features in their behavior. Activity diagrams do these things very well. A single path through a use case, by definition, doesn't have simultaneous behaviors and decision points, so a sequence diagram is more appropriate.
Googling "use case scenario sequence diagram" gives a number of links that explain the use of sequence diagrams for use case scenarios in detail, of which this is an example.
UseCase is declaration of behavior (service or usefull behavior) of system which is executed by system with collaboration (interaction) with system's actors.
Any type of diagram defined in UML could by used to describe behavior on any level of abstraction. All of diagrams could be also used to describe both business or technical aspects of system.
UseCase is declaration of behavior, it means that UseCase does not define behavior at all. UML does not define scenarios of UseCase ,scenarios are usually defined in methodology not in UML.
If you need to describe behavior of system in context of UseCase you can use some of behavior diagrams defined in UML for each UseCase.
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 am new to UML. I have studied more tutorials.I learned two broad categories like,
UML Diagrams:
1. Structural Diagrams
Class diagram
Object diagram
Component diagram
Deployment diagram
2. Behavioral Diagrams
Use case diagram
Sequence diagram
Collaboration diagram
Statechart diagram
Activity diagram
But I dont know which one is high level design and low design. Anyone list out the UML diagram types based on priorities. (high-level diagrams to low level)
There is not really a well-defined order of higher-level versus lower-level diagram languages in UML. The same diagram language (e.g. class diagrams) can be used at different levels of abstraction. For instance, a conceptual information model, but also a Java data model, can be expressed as a class diagram.
Generally, a use case diagram is higher-level, since it describes requirements, while a deployment diagram is lower-level, since it describes system deployment structures.
But all other diagrams languages can be used at different levels of abstraction.
UML diagrams - from the most common to most detailed level.
Please, notice, that nowadays (the start of 2014) there are no special instrument for UI modelling. So, I'll explain how to do this part of work, too, with the tools we have. But they will be used in a less or more nonstandard way.
Human level. Use case diagrams and state machines. How people will work with the system.
Use cases are about what the system does, who works with it and maybe, grouping of those subjects. Subsystems can be defined here. Try not to show much structure or behaviour. Not to use any IT slang!
State machines show what states the system, subsystems and actors can have and what actions/events can happen in these states and to which other states can it lead. Not to use any IT slang!
Do not forget, that administrators, programmers and testers are users of the system, too. So, plan not only how the system helps to the work of the common user and his senior, but also to the installation/administration/testing/support processes. Don't forget to continue this work on all deeper diagraming levels. These use cases/state machines needn't be so human-oriented.
You can draw activities, sequence, timing diagrams for some dialogues between Actors and subsystems, if they are the part of the requirements. Or make them the part of requirements if they are important. Not to use any IT slang!
Draw the sketches for the UI and talk over them with client. The work on UI art design should be connected to UI planning and realization
Start to work on User Guide - create plan and structure. (I use class diagrams for that).
Deployment and component diagrams. Here you are starting to imagine the inner construction of your system
Components - What compact parts it has. It needn't have much in common with the subsystems, as user see them. Only some components are visible to the user. You could decide on the use of some interfaces between them. Think on the license problems of the third-party components.
Deployment - how the components could be distributed among PCs. The same question about interfaces, but more from the physical side.
A special deployment diagram for license politics of your product could be drawn, too. You can use other diagrams for it, as well. It is at your choice.
You could already plan your user interface by these diagrams, too. In MVC (model-viewer-controller) construction only the components of the controller level are mutually connected and obviously need this level modelling. But the viewer layer (UI) components are connected in a conceptual way, they should be, for the sake of user. So, it should be planned too, by the same diagrams.
On this level you also plan the architecture of the development environment. It consists of components, too.
Draw Interaction Overview and Communication diagrams to see the cooperation of components as a whole or in complex groups.
Package, activities, sequence, timing diagrams
Package diagrams are for planning the hierarchy of your code and mutual visibility of its parts. Don't forget the place for testing packages, too. Notice, that the structures of packages and components hierarchies are different, but they have to work together. It is very important part, frequently overlooked.
Use behavioral diagrams for better understanding how different processes could run.
System analysis - the class diagrams level.
Some important classes could appear on the previous level diagrams - as definitions of intercomponent interfaces or subjects of processes. But now you should do all of them. Minimally a diagram for a component. You should do these class diagrams, using ready package diagrams.
Plan the content of UI, defining elements and functonalities and connections between them WITHOUT choosing the concrete components. Use diagrams that you like. Class ones are usable, but in not standard reading.
Deeper insight
If you have instances with specific behavior, use Object diagrams for their planning.
If you have some very complex classes or their tight groups, use Composite Structure Diagrams.
UI: Plan the content of screen elements WITH choice of the UI components (frames, buttons and so on) and connecting functionalities to them. On this level you can again use class/object and sequence/timing diagrams.
Code. Really, the coding, at least on the prototype level starts already on the stage of component planning. You have to control if and how different technologies will cooperate. But the real coding should be done only after you are sure you understand what are you doing. And to create all or some correct diagrams is the best way to be sure in it.
Notice the rule of thumb - structure diagrams set the sequence of levels. Behavioral diagrams support them on all levels. You can use state machine on the lowest level and timing diagram for to discuss with a client. But try not to mix the levels with the structural diagrams!
Also, do not try to mix diagrams, especially behavioral with structural ones. You should clearly set the rules, by which you can say, what part of information can be on the diagram and what not. And break these rules really only in the most exceptional cases.
As gwag noted, there is no separation of UML diagrams into high and low levels. The different diagrams are used for describing different aspects, not different levels, of a (software) system.
But if you look at UML in a broader context, the Unified Modelling Language is just one of a whole family of modelling languages standardized by OMG. These different languages do have more specific scopes.
SysML (Systems Modelling Language) shares many features with UML and looks very similar, but is specifically intended for the higher levels of systems analysis / design. It also includes a visual representation of requirements, which are conspicuously absent from UML.
Another related language is BPMN (Business Process Model and Notation), which is used for business processes. So you could for instance use BPMN for business analysis, SysML for system design and UML for software design.
UML does not specify level of details you define in diagram. Every diagram can be used for description on business level, implementation or design level as well.
It is up to modeler, what type of diagram uses to descrbe modeled system. Information in diagrams must correspond with each other and all diagrams must give complet view on system.
For example, you can declare services of Bank company using UseCase on business level or use UseCase to declare services implemented by concret physical component of program writen in Java.
I am trying to build a class diagram from use case. But I am not sure if I should include the system in class diagram. I have system as actor in use case diagram. If I include it in the case diagram can I use it without attributes....
"I have system as actor in use case diagram" - Actor can be human or non-human system external to your subject that is your whole system. For example, card payment system or buyer are actors for net stores. You can show your system in the use case diagram, too, but it will be a rectangle, containing ALL use cases - not really so much useful thing. But showing of SUBsystems can be useful.
Later you can draw a deployment diagram - if different subsystem lie on different computers. And maybe, some dynamic diagrams of how they talk to each other and actors.
If we are talking on static diagrams, your next step will be component diagram - you'll divide your system in smaller parts and show who talks to who and here already the classes of messages being sent can appear.
Later - you'll plan what packages will contain your classes and what will be visible from which. Package diagram.
Later - yes, at last we are here - you create the class diagram(s). Maybe, several - for different components. So, you are a bit too in a hurry.
Sometimes, especially, if you work with some special objects of some class(es), you need Object Diagram.
And don't forget - there are also dynamic diagrams, I have mentioned static ones only.
Can you please elaborate your question with specific example in order to get better knowledge about the scenario?
As far my knowledge, one can use the system such as any controller class which is again an actor here as class in the class diagram.
"I am trying to build a class diagram from use case"
Use-cases are a very abstract and user-centric view of the system while class diagrams are fine-grained and technically focused.
So you should not try to infer your classes directly from a UC diagram. Instead, use the repertoire UML gives you (component-, activity-, sequence diagrams etc.)
In my experience, I usually create Object interaction Diagram from Use Cases. Mostly, the nouns on the Use Cases are Classes ... In Object Interaction Diagrams, I can have clear ideas about the methods and lifespan of the Classes ...
"Object Interaction Diagrams" or "Interaction Diagrams" are usually to elaborate a single use Case ..
A simple google search gave me this link and it gives you some idea ...
http://www.cs.unc.edu/~stotts/145/CRC/Interactions.html
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.