Thursday, June 10, 2010

Working with sequence diagrams in UML, How to Create Sequence Diagram? About Sequence Diagram

The sequence diagram consists of objects represented in the usual way- as named rectangles (with the name underlined), messages represented as solid line arrow, and time represented as a vertical progression.
The following figure depicts the arrangement of objects and messages in a sequence diagrams.
• Header Elements of sequence diagrams.
Actor: -indicate an external person or entity that negotiate with the system .

Object: -Represents an instance in the system or one of its components.

Unit:-Represents a subsystem, component, unit, or other logical entity in the system (may or may not be implemented by objects)

Separator: - Represents an interface or boundary between subsystems, components or units (e.g., air interface, Internet, network)
Group: -Groups related header elements into subsystems or components.
Body Elements in Sequence Diagram.

Action: -Represents an action taken by an actor, object or unit.
Asynchronous: - An asynchronous message between header elements.
Block: -A block represents a loop or conditional for a particular header element.
Call message:-A call (procedure) message between header elements.
Create message: - A "create" message that creates a header element (represented by lifeline going from dashed to solid pattern).

Destroy Element: - Represents the destruction of a header element.
Destroy Message: -Represents the destruction of a header element as a result of a call from another element.
Diagram Link: - Represents a portion of a diagram being treated as a functional block Similar to a procedure or function call that abstracts functionality or details not shown at this level can optionally be linked to another diagram for elaboration.
Else Block: - Represents an "else" block portion of a diagram block.

Message return: - A return message between header elements.


What is recursion?
Sometimes an object has an operation that invokes itself. This is called recursion.

Following figure show the recursion in sequence diagrams.

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