Lecture11 use case sequence diagram

Use Case Sequence Diagram

Interaction Diagrams q Interaction diagrams model the behavior of use cases by describing the way groups of objects interact to complete the task of the use case. q There are two types of interaction diagrams q Sequence Diagrams and Communication Diagrams (formally known as collaboration diagrams)

Interaction Diagrams q Sequence diagrams • generally show the sequence of events that occur. q Collaboration diagrams demonstrate how objects are statically connected. q Both diagrams are relatively simple to draw and contain similar elements.

Sequence Diagram q Illustrates the objects that participate in a use case and the messages that pass between them over time for one use case q In design, used to distribute use case behavior to classes

Sequence Diagram member: LibraryMember book:Book :Book Copy borrow(book) ok = mayBorrow() [ok] borrow(member) setTaken(member) X-Axis (objects) Y-Axis(time) ObjectLife Line Message Focus of control Condition

Sequence Diagram Syntax AN ACTOR AN OBJECT A LIFELINE A FOCUS OF CONTROL A MESSAGE OBJECT DESTRUCTION anObject:aClass aMessage() x

Sequence Diagram Two major components • Active objects • Communications between these active objects • Messages sent between the active objects

Sequence Diagram Active objects • Any objects that play a role in the system • Participate by sending and/or receiving messages • Placed across the top of the diagram • Can be: • An actor (from the use case diagram) • Object/class (from the class diagram) within the system

Active Objects Object • Can be any object or class that is valid within the system • Object naming • Syntax [instanceName][:className] 1. Class name only :Classname 2. Instance name only objectName 3. Instance name and class name together object:Class myBirthdy :Date

Active Objects Actor • A person or system that derives benefit from and is external to the system • Participates in a sequence by sending and/or receiving messages

Communications between Active Objects Messages • Used to illustrate communication between different active objects of a sequence diagram • Used when an object needs • to activate a process of a different object • to give information to another object

Messages A message is represented by an arrow between the life lines of two objects. • Self calls are allowed A message is labeled at minimum with the message name. • Arguments and control information (conditions, iteration) may be included.

Types of Messages  Synchronous (flow interrupt until the message has completed)  Asynchronous (don’t wait for response)  Flat (no distinction between sysn/async)  Return (control flow has returned to the caller)

Synchronous Messages q The routine that handles the message is completed before the calling routine resumes execution. :A :B doYouUnderstand() Caller Blocked return (optional)yes

Asynchronous Messages  Calling routine does not wait for the message to be handled before it continues to execute.  As if the call returns immediately  Examples  Notification of somebody or something  Messages that post progress information

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, e.g. ok = isValid()

Other Elements of Sequence Diagram  Lifeline  Focus of control (activation box or execution occurrence)  Control information  Condition, repetition

Sequence Diagram  Lifeline  Denotes the life of actors/objects over time during a sequence  Represented by a vertical line below each actor and object (normally dashed line)  For temporary object  place X at the end of the lifeline at the point where the object is destroyed

Sequence Diagram  Focus of control (activation box)  Means the object is active and using resources during that time period  Denotes when an object is sending or receiving messages  Represented by a thin, long rectangular box overlaid onto a lifeline

Control Information  Condition  syntax: ‘[‘ expression ’]’ message-label  The message is sent only if the condition is true [ok] borrow(member)

Elements of Sequence Diagram obj1:Class [x < 15] calculate() obj2: Class message()

Sequence Diagrams obj1:Class [x < 15] calculate() obj2: Class message() obj3: Class [x > 20] calculate()

Sequence Diagrams q Concurrency obj1:Class calculate() obj2: Class message() obj3: Class calculate()

Elements of Sequence Diagram  Control information  Iteration  may have square brackets containing a continuation condition (until) specifying the condition that must be satisfied in order to exit the iteration and continue with the sequence  may have an asterisk followed by square brackets containing an iteration (while or for) expression specifying the number of iterations

Control Information  Iteration  syntax: * [ ‘[‘ expression ‘]’ ] message-label  The message is sent many times to possibly multiple receiver objects. *draw()

Control Information  Iteration example :Driver *[until full] insert() :Bus:CompoundShape :Shape *draw() draw()

Sequence Diagrams  Creation and destruction of an object in sequence diagrams are denoted by the stereotypes <<create>> and <<destroy>> :Creator <<create>> : Created Object message() <<destroy>> X

getViolation(id) Sequence Diagram Clerk :Violations Dialog :Violations Controller :Violations DBProxy lookup viewButton() id=getID() v:Traffic Violation display(v) <<create>> v Lookup Traffic Violation DB is queried and the result is returned as an object

Steps for Building a Sequence Diagram 1) Set the context 2) Identify which objects and actors will participate 3) Set the lifeline for each object/actor 4) Lay out the messages from the top to the bottom of the diagram based on the order in which they are sent 5) Add the focus of control for each object’s or actor’s lifeline 6) Validate the sequence diagram

1) Set the context. a) Select a use case. b) Decide the initiating actor. Steps for Building a Sequence Diagram

2) Identify the objects that may participate in the implementation of this use case by completing the supplied message table. a) List candidate objects. 1) Use case controller class 2) Domain classes 3) Database table classes 4) Display screens or reports Steps for Building a Sequence Diagram

Steps for Building a Sequence Diagram 2) Identify the objects (cont.) b) List candidate messages. (in message analysis table) 1) Examine each step in the normal scenario of the use case description to determine the messages needed to implement that step. 2) For each step: 1) Identify step number. 2) Determine messages needed to complete this step. 3) For each message, decide which class holds the data for this action or performs this action 3) Make sure that the messages within the table are in the same order as the normal scenario

Steps for Building a Sequence Diagram 2) Identify the objects (cont.) c) Begin sequence diagram construction. 1) Draw and label each of the identified actors and objects across the top of the sequence diagram. 2) The typical order from left to right across the top is the actor, primary display screen class, primary use case controller class, domain classes (in order of access), and other display screen classes (in order of access) 2) Set the lifeline for each object/actor

4) Lay out the messages from the top to the bottom of the diagram based on the order in which they are sent. a) Working in sequential order of the message table, make a message arrow with the message name pointing to the owner class. b) Decide which object or actor initiates the message and complete the arrow to its lifeline. c) Add needed return messages. d) Add needed parameters and control information. Steps for Building a Sequence Diagram

5) Add the focus of control (activation box) for each object’s or actor’s lifeline. 6) Validate the sequence diagram. Steps for Building a Sequence Diagram

Sequence Diagrams :Cashier makenewSale() : System enterItem(itemID, quantity) description, total endSale() total makePayment(amount) change due, receipt

Lecture11 use case sequence diagram

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