Lecture 4 Sequence Interaction Diagrams.ppt

Lecture 4 Sequence Interaction Diagrams.ppt

1. Copyright W. Howden 1
Lecture 4: Sequence Interaction
Diagrams

2. Copyright W. Howden 2
Behavioral vs Static Models
•Describe interactions
between entities
•Sequence Diagrams
•Collaboration
Diagrams
•Message Sequence
Charts
•State Charts
•Describe structure of
complex entities
•Class Diagrams
•Entity-relationship
models

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Sequence Diagrams -
Components
•Objects
–Actors, subsystems, class instances
•Messages
–One object sends a message to another message
•Each diagram describes a scenario, or what
happens during a use of the system
•System described by a collection of
diagrams

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: Member
: GUI : DomainLogic : DataBase
setMemberData()
setMemberData(dateeData, name)
getMemberData(name)
upDateMemberData(memberData)
Set member data scenario
Preceded by and
followed by
LogOn and
LogOff scenarios

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Applicability
•System/Actor interaction
–Requirements elaboration
•Subsystem interactions
–Requirements elaboration and design
•Subsystem design
–Object properties and class visibility

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System Actor Interaction
•Investigate the interactions the user has with
the system
•Specify the needed user interface forms
–Specify contents/capabilities of GUI before
graphical design
•Following example note: In the
actor/system interaction we see self-
messages notation

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Subsystems Interaction
•Show the messages that the subsystems
send back and forth
•Enforce a layers architecture
•Identify the subsystems interface/proxy
•In the following example we see the
alternatives notation, which allows multiple
related flows to be included in

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Additional Examples
•Get a Date Scenario
–Includes conditionals allowing alternative paths
in same scenario/ISD
•Start up Scenario
–Shows interactions with system
•Log On Scenario
•Exit/Log Off Scenario

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: User
: Start : GUI : System
DatingSystem
Execute(main)
create()
Start up scenario
At this point follow
LogOn/LogOff scenarios
show()

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: User
: GUI : DomainLogic : DataBase : System
display Start/End
End
Log Off scenario
exit()

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Additional Notation
•Focus of Control
–Indicate when an object’s lifestream is “active”
•Data return from a sent message
•Iteration of message

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: Member : GUI : DomainLogic : DataBase
getDate()
displayOptionChoice()
dsiplayDaterPreferencesForm()
daterPreferences()
getDate()
memberData:=getFirst()
memberData:=*getNext()
searchResult
[null] displaySorry()
[notNull] displayDateProps()

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Systematic Object Identification
for Sequence Diagrams
•Rational Software approach (Rational now
part of IBM and source of Rational Unified
Process)
•Four kinds of objects
–Actor
–Boundary/Form
–Entity/Data
–Control

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Boundary Objects
•Place where the actors interface with the
system
•Referred to as forms by some methods

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Entity
•Data type objects
•Place where information is stored
•Data Bases

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Control
•Coordinates the activities of the use case
•Often identified with a use case, with one
per use case
•Possible controller objects in O/O
–Use Case, Role, System/subsystem, and
Business

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Actor Control Entity/Data 1 Entity/Data 2
Open
Form
Enter information
Save/Process
Save/Process
Create
Populate
Access/Retrieve
Message1

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Additional Notations – Message
Synchronization
•Synchronous: sender waits until receiver has
processed message
•Procedure call: receiver is ready to receive call,
sender waits for return from call. A kind of
synchronous
•Asynchronous: sender sends message and then
continues regardless of status of receiver
•Balking: if receiver is not ready to receive
message it is abandoned

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Application to Distributed
Systems
•Sequence diagrams show collections of
interactions between components in system,
like subsystem interaction diagrams
•Can use to develop specifications for
components, with individual state diagrams

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DS Scenarios For
Distributed System
•Scenario 1
–User who is a member logs on and asks for a date. A
date is found. Client relies on server to supply first and
subsequent records from member Data base.
•Scenario 2
–User logs on who is not a member. Then a user who is
a member logs on. The client eventually asks the
server for the next record and nil is returned since there
are no more. Client displays a sorry-no-date message.

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Developing a State Model
Specification for a Component
•Factor the sequence diagrams, e.g. for the
Client, get all the client lifelines
•Decide where the states are
–E.g. For Client, each new GUI Frame?
•Not always an exact match with the traces
–After each message received

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