Sequence diagram example

Sequence diagram
2012 pavasaris
What is the purpose of sequence
diagram ?
• The sequence diagram is used primarily to show the
interactions between objects in the sequential order
that those interactions occur.
• Developers think sequence diagrams were meant
exclusively for them :-)
• Business staff can find sequence diagrams useful to
communicate how the business currently works by
showing how various business objects interact.
• A business-level sequence diagram can be used as a
requirements document.
• During the requirements phase use cases are often
refined into one or more sequence diagrams.
Sequence vs. Activity?
• Little bit later…
Notation 1/
• An empty frame
• Lifeline
Notation 2
• Sending a message/methos to another object
• The name is placed above the arrowed line
• And represents an operation/method that the
receiving object's class implements.
Notation 3
• Return messages – optional
• The use of return messages depends on the
level of detail/abstraction
• Return value is placed above dotted line
Notation 4
• Sending a message to itself
• the model draws attention to the fact that this
processing takes place in the system object.
Notation 5
• Asynchronous message
Notation 6
• Who will guard the guardians themselves?
• Who will guard the guardians themselves
Combined fragments (alternatives,
options, and loops)
• A combined fragment is used to group sets of
messages together to show conditional flow
in a sequence diagram.
• Alternatives - classic "if then else" logic
• Options - a simple "if then" without “else”
• Loops – a repetitive sequence
• mutually exclusive
choice between
• used to model a
sequence that,
given a certain
condition, will
occur; otherwise,
the sequence
does not occur.
• does not require guard condition be placed on it
• a guard can have two special conditions
• Minint = 1, Maxint = 5
• most commonly used to model exception handling
• cause the exiting of an enclosing interaction's
• In cases where a break is part of combined fragment,
then only that fragment is exited.
Nested diagrams
• Referencing another sequence diagram
Sequence(SD) vs. activity (AD)?
• AD mainly represent process flows.
• SD mainly represent step by step ordered in
time interaction between different objects.
• AD also repersents an object role in workflow
but level of repersenation is not dynamic like
• Example: Object lifeline and detailed
sequence of interaction
Facebook user
in a Web
Submit comments (AJAX)

similar documents