18-06-2014, 03:24 PM
Sequence Diagrams
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Agenda
Interaction Diagrams
A First Look at Sequence Diagrams
Objects
Messages
Control Information
Examples
Interaction Diagrams
A series of diagrams describing the dynamic behavior of an object-oriented system.
A set of messages exchanged among a set of objects within a context to accomplish a purpose.
Often used to model the way a use case is realized through a sequence of messages between objects.
The purpose of Interaction diagrams is to:
Model interactions between objects
Assist in understanding how a system (a use case) actually works
Verify that a use case description can be supported by the existing classes
Identify responsibilities/operations and assign them to classes
UML
Collaboration Diagrams
Emphasizes structural relations between objects
Sequence Diagram
The subject of this tutorial
A First Look at Sequence Diagrams
Illustrates how objects interacts with each other.
Emphasizes time ordering of messages.
Can model simple sequential flow, branching, iteration, recursion and concurrency
Object
Object naming:
syntax: [instanceName][:className]
Name classes consistently with your class diagram (same classes).
Include instance names when objects are referred to in messages or when several objects of the same type exist in the diagram.
The Life-Line represents the object’s life during the interaction
Messages
An interaction between two objects is performed as a message sent from one object to another (simple operation call, Signaling, RPC)
If object obj1 sends a message to another object obj2 some link must exist between those two objects (dependency, same objects)
A message is represented by an arrow between the life lines of two objects.
Self calls are also allowed
The time required by the receiver object to process the message is denoted by an activation-box.
A message is labeled at minimum with the message name.
Arguments and control information (conditions, iteration) may be included.
Return Values
Optionally indicated using a dashed arrow with a label indicating the return value.
Don’t model a return value when it is obvious what is being returned, e.g. getTotal()
Model a return value only when you need to refer to it elsewhere, e.g. as a parameter passed in another message.
Prefer modeling return values as part of a method invocation,
Synchronous Messages
Nested flow of control, typically implemented as an operation call.
The routine that handles the message is completed before the caller resumes execution
Object Destruction
An object may destroy another object via a <<destroy>> message.
An object may destroy itself.
Avoid modeling object destruction unless memory management is critical.
Control information
Condition
syntax: ‘[‘ expression ’]’ message-label
The message is sent only if the condition is true
example:
Iteration
syntax: * [ ‘[‘ expression ‘]’ ] message-label
The message is sent many times to possibly multiple receiver objects.
The control mechanisms of sequence diagrams suffice only for modeling simple alternatives.
Consider drawing several diagrams for modeling complex scenarios.
Don’t use sequence diagrams for detailed modeling of algorithms (this is better done using activity diagrams, pseudo-code or state-charts).