Behavioral UML diagrams

Behavioral diagrams basically capture the dynamic aspect of a system. Dynamic aspect can be further described as the changing/moving parts of a system.

Behavior diagrams emphasize what must happen in the system being modeled —

♦ Activity diagram: represents the business and operational step-by-step workflows of components in a system. An activity diagram shows the overall flow of control.

♦ State diagram: standardized notation to describe many systems, from computer programs to business processes.

♦ Use case diagram: shows the functionality provided by a system in terms of actors, their goals represented as use cases, and any dependencies among those use cases.

Since behaviour diagrams illustrate the behaviour of system, they are used extensively to describe the functionality of software systems.


Interaction diagrams

Interaction diagrams, a subset of behavior diagrams, emphasize the flow of control and data among the things in the system being modeled:

♦ Communication/Collaboration diagram: shows the interactions between objects or parts in terms of sequenced messages. They represent a combination of information taken from Class, Sequence, and Use Case Diagrams describing both the static structure and dynamic behavior of a system.

♦ Interaction overview diagram: is a type of activity diagram in which the nodes represent interaction diagrams.

♦ Sequence diagram: shows how objects communicate with each other in terms of a sequence of messages. Also indicates the lifespans of objects relative to those messages.

♦ Timing diagrams: is a specific type of interaction diagram, where the focus is on timing constraints.

UML has the following five types of behavioral diagrams −

  • Use case diagram
  • Sequence diagram
  • Collaboration diagram
  • State diagram
  • Activity diagram


Use Case Diagram

Use case diagrams are a set of use cases, actors, and their relationships. They represent the use case view of a system.

A use case represents a particular functionality of a system. Hence, use case diagram is used to describe the relationships among the functionalities and their internal/external controllers. These controllers are known as actors.


Sequence Diagram

A sequence diagram is an interaction diagram. From the name, it is clear that the diagram deals with some sequences, which are the sequence of messages flowing from one object to another.

Interaction among the components of a system is very important from implementation and execution perspective. Sequence diagram is used to visualize the sequence of calls in a system to perform a specific functionality.


Collaboration Diagram

Collaboration diagram is another form of interaction diagram. It represents the structural organization of a system and the messages sent/received. Structural organization consists of objects and links.

The purpose of collaboration diagram is similar to sequence diagram. However, the specific purpose of collaboration diagram is to visualize the organization of objects and their interaction.


State Diagram

Any real-time system is expected to be reacted by some kind of internal/external events. These events are responsible for state change of the system.

State diagram (or Statechart diagram) is used to represent the event driven state change of a system. It basically describes the state change of a class, interface, etc.

State diagram is used to visualize the reaction of a system by internal/external factors.


Activity Diagram

Activity diagram describes the flow of control in a system. It consists of activities and links. The flow can be sequential, concurrent, or branched.

Activities are nothing but the functions of a system. Numbers of activity diagrams are prepared to capture the entire flow in a system.

Activity diagrams are used to visualize the flow of controls in a system. This is prepared to have an idea of how the system will work when executed.