UML Interaction modeling using OSDs

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UML - Interaction modeling using OSDs

• Format of lecture
• Over Last 2 week Ive introduced dynamic modeling
  to you in in the form of State Diagrams
• This week we continue this theme with a new
  diagram to consider called an Object Sequence
  Diagram (OSD)
• Object Interaction is also dynamic behaviour
  modeling
• It is used to show the interactions which occur
  between the static Class Diagram and the Use
  Cases
• Why useful?
• This integration of the users view (Use Case
  model) and the developers view(Class Diagram) is
  used to cross check the requirements of the
  system
• There will be a demo of an OSD using Visio
• This week is just the intro followed by more next
  week

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Interaction modeling

• As we have seen and used.
• The Class Diagram for a problem defines the
  internal structure of the objects (by defining
  the class content) but does not show how the
  objects will interact
• Use Cases depict the processes without concern
  for the internal composition of the processes
• Interaction modeling increases the chances of the
  system achieving what the user wanted

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Interaction modeling

• Object interaction modeling involves two types of
  modeling diagram derived from Use Cases
• Object Sequence Diagram(OSDs)
• Object Collaboration Diagram(OCDs)
• We are just following OSDs

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Object Sequence Diagram

• Illustrate how objects interact with each other
• Focuses on message sequence

Part of an OSD
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Object Messages

• Messages are fundamental to OO see first weeks
  lecture but to recap
• What is a message?
• a communication between objects that conveys
  information
• has a sender and recipient(analogy with client
  and server)
• is represented as an arrow denoting flow of
  control

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Object Sequence Diagram

• The Object Sequence Diagram(OSD) represents a
  graphic description of a Use Case - this is
  useful
• It has description constructs of sequence,
  selection and iteration
• passage of time also depicted on the diagram by
  the flow of messages
• So it does the things the Use Case Diagram could
  not
• Why use them?
• As developer we can look at the OSD to see what
  objects(derived from Classes) make up a process(a
  transaction) and the sequence of how they are
  used.
• Let us briefly review a Hotel booking example
  problem

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Hotel System Example - Use-case view

• Hotel UCD

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Hotel System Example - Use Cases

• Check_in use case
• This use case begins when a visitor enters the
  hotel.
• The system checks if the visitor had booked a
  room.
• If yes then the S1. If not the system checks if
  there are free rooms. If yes the room is reserved
  for the visitor and the S1. If not the case is
  finished with the message - NO Vacancies.
• S1. Room is allocated to the visitor. Message
  GIVE KEY is send to the receptionist. The visitor
  receives a VISITORS CARD.
• Check_out use case
• This use case begins when a visitor arrives at
  the reception desk in order to check out the
  hotel.
• The system calculates the bill. The visitor pays.
  The system sends a message to the cleaner to
  clean up the left room. COLLECT KEY is send to
  the receptionist. The visitor returns the key the
  visitors card.

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Classes identified

• Hotel
• Hotel has one or more Hotel Guest
• Hotel has many Rooms
• Hotel has employees - Receptionist and Cleaner

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Hotel System Example - Class Diagram initial
Hotel
available (r Room)
1
1
guests
Room
Cleaner


HotelGuest
size Number
pay Money
clean Bool
leave ()
clean (r Room)
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Hotel Example - Class diagram further developed
inheritance

• Persons involved

Need to put Room Class on here as well
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Hotel Example - State Diagram

• Room class chosen to be modelled

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Hotel Example Object Sequence Diagram
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Sequence Diagram

• Purpose
• capture the behaviour of a single use case -
  how messages are sent within a use case
• show how objects interact with each other - show
  how they send and receive messages
• focus on time

• Syntax
• object
• time
• message

• Forms
• generic - all possible alternative scenarios
• instance - one scenario, no conditions, branches,
  loops

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Object Sequence Diagram

• Making a
• telephone
• call Use Case
• example

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Sequence Diagram

• Types of messages
• simple
• flat flow of control - control is passed without
  describing any details
• synchronous
• nested flow of control - operation call
• handling of the message is completed before the
  caller resumes execution
• asynchronous
• there is no explicit return to the caller
• the sender continues to execute after sending the
  message without waiting for it to be handled

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Sequence Diagram

• Activation
• time during which object performs an action
  either directly or through another object
  (subcontractor)

• Return
• implicit
• explicit

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Sequence Diagram

• Purpose
• capture the behaviour of a single use case -
  how messages are sent within a use case
• show how objects interact with each other - show
  how they send and receive messages
• focus on time

• Syntax
• object
• time
• message

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Tutorial - To create OSDs

• Select a Use Case (Use Case Script) to be
  modelled
• From UCD script description you have the
  Sequence, Select and Iteration
• Draw Classes onto OSD diagram along the top
• Add messages to the diagram
• Remember TIME runs vertically downwards
• Do an initial draft first and then think about
  refining it

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For the Assignment

• You have all the things necessary to make one
  OSD
• Use Cases from the Use Case Diagram work
• Use Case Scripts
• Business Classes (and Interface Classes) from the
  Class Diagram work
• Re messages and the Operation/Events from the
  Class Diagram work and State Diagram work
• More next week in the consolidation session about
  how to build one