System Behaviour Analysis

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Behavioural diagrams describing the system behaviour, i.e. the dynamics of the system.


The dish

Activity diagrams

State Machine diagrams

Sequence diagrams



Identify and list the internal work flows, business rules or logic of the system-to-be. Use the open minded model described earlier.

Describe all work flows, business rules or logic of the system in the necessary number of activity diagrams.

UML has a number of diagrams that can be used to express the behaviour of a system. The Use Case diagram in general expresses the different use cases for the system-to-be, but it is a static mapping of the system. Use cases may on the other hand be a good inspiration to find candidates of different behaviour of the system-to-be.

Communication Diagrams expresses how the external world interacts with the system-to-be and often also in what sequence.

Activity Diagrams expresses the behaviour of the system-to-be or parts of the system-to-be, i.e. several activity diagrams may be used to express the complete behaviour of the system-to-be.

State Machine Diagrams is typically used to express the shifting states of a block, a class or a module. Please note that state machine diagrams also can be used to identify general system states covering the whole system or vital parts of the system.

Sequence Diagrams is also very useful to express behaviour of a system or parts of a system. The sequence diagrams makes it easy to see the order of execution and the parts involved in the execution.


The architecture block diagrams shows a static view of the system. The activity diagrams show the behaviour of the system - the dynamics of the system.

As vital as the static block diagram the behaviour of the system is. No system does not have some kind of behaviour.

With the behavioural diagrams the developer gains knowledge of how the system-to-be shall behave while in operation.



An example of one activity of a bigger system

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Example of complex updates in a system. Note it is possible to identify an idea of timing in the sequence diagram

States and events (or transitions).jpg

Systems often goes through different states in its lifetime. State Machine diagrams can express a block, a class or a modules states during execution.

State Machine diagrams can also be used to express states of larger parts of a system, but often Activity Diagrams may be a better option.

References and inspiration

Tutorialspoint has a number of pages on UML diagrams.

UML diagrams describes the UML version 2.5 diagram types and their usage.