How to categorized the UML diagrams based on priorities/ levels?

Question

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)

Answer 1

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.

Answer 2

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.

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• 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.

Answer 3

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.

Answer 4

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.