Object Oriented System Design COS 503

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Object Oriented System Design COS 50-3

• Marc Conrad
• D104 (Park Square Building)
• Marc.Conrad_at_luton.ac.uk
• Acknowledgement slides on this weeks lecture
  mostly provided by Dayou Li.

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Sequence Diagram

• A sequence diagram shows how blocks (objects)
  within a use case cooperate with each other. It
  shows the occurrence of a sequence of events as
  the responses to stimuli, which is called
  stimuli-responses relationship or the internal
  logic of a system.
• A stimulus comes from a block and goes to another
  block. It triggers a sequence of events in that
  block.
• The receiver may also send results (feedback)
  back to the sender.
• Events must be known before constructing a
  sequence diagram.

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Sequence Diagram (Contd)
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Sequence Diagram

• Sequence diagram shows how blocks (objects)
  within a used case cooperate with each other. It
  shows the occurrence of a sequence of events as
  the responses to stimuli, which is called
  stimuli-responses relationship or the internal
  logic of a system.
• A stimulus comes from a block and goes to another
  block. It triggers a sequence of events in that
  block.
• The receiver may also send results (feedback)
  back to the sender.
• Events must be known before constructing a
  sequence diagram.

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Sequence Diagram (Contd)
Syntax and Semantics
signal (interprocess)
Blocks life line (showing life cycle)
message (intra-process)
Distinguishing a system and the outside
world (RationalRose Use Actors )
Events occurring within a block
feedback signal
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Sequence Diagram (Contd)
Pragmatics

• List all blocks right-hand side of the system
  border,
• Draw a life line for each block,
• List all events on the left-hand side of the
  system border,
• Draw vertical bars on the corresponding life
  lines to represent the events.
• Identify and draw signals,
• Identify and draw messages,
• Identify and draw feedback signals.

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Sequence Diagram (Contd)
Example (focusing on Returning item use case)

• Blocks
• -- Customer Panel,
• -- Deposit item receiver,
• -- Receipt basis,
• -- Deposit item,
• -- Receipt printer.

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Sequence Diagram (Contd)

• Events (when a customer insert an item)

If (customer is new) Create a new
account Do If (returned item is
acceptable true) Classify Increment
items Increment values else reject
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Sequence Diagram (Contd)

• Events (when the customer presses receipt
  button)
• Print Logo and date
• for (index 0 index lt 3 index )
• Find name and number for a type of item
• Find deposit value for a type of item
• Sum
• Print sum
• Ready for the next customer

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Sequence Diagram (Contd)
create
A new customer press start button
ready
new item
Do check classify Increment items, Increment
values, While (! receipt button pressed)
Item
items
inc item/value
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Sequence Diagram (Contd)
receipt
The customer presses the receipt button
printReceipt
print Logo, date
Print Logo and date, Find name and number for a
type of item, Find deposit value for a type of
item, Sum, Print sum
get value
value
get name
name
print
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Sequence Diagram (Contd)
receipt
The customer presses the receipt button
printReceipt
print Logo, date
Print Logo and date, Find name and number for a
type of item, Find deposit value for a type of
item, Sum, Print sum
get value
sum
value
get name
name
printSum
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Rational Rose Sequence Diagram
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Rational Rose Collaboration Diagram
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Case Study (Vehicle Hire Company)
EuroStar is a vehicle hire company. It provides a
variety of vehicles for its customers. Each
vehicle has a record in the companys database,
including Register Number, Maker, Model, Colour,
Engine Size, etc. The company has a manager and
a number of Register Staff. The register staff
takes a customers reservation and searches for a
vehicle that matches the order by sending a query
to the companys computerised database. When the
requested type of vehicle is available, the staff
confirms the reservation. If it is not available,
the staff gives suggestions of alternative
vehicle.
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Case Study (Vehicle Hire Company)
Customers are required to return vehicles to the
company before a Return Time. They are liable to
a fine if they return vehicles late. EuroStar
now wants to have a Web site in order that
customers can make their reservation through the
Internet. Suppose that you are working in a
software house and EuroStar is your client. You
are asked to develop such an on-line booking
system for the company.
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Requirement Model (use case)
-- customers
-- making a reservation
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Analysis Model (3-type objects)
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Design Model (sequence diagram)

• Events
• read customers request,
• form a query,
• search for a vehicle,
• find alternative if the request vehicle is
  unavailable,
• display alternative vehicle,
• set return time,
• display return time.

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Design Model (sequence diagram)
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COS50-3 OOSD
Object Oriented Design Model II (Week 5)
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Selection in SD

• If else
• Fork and condition repression.
• Branch of control in the receiving blocks
  lifeline.

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Selection in SD (Contd)
A soda machine example Customers buy soda drinks
from a soda machine.
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Selection in SD (Contd)
When input (inserted coins ) price
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Selection in SD (Contd)
When input (inserted coins ) gt price
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Selection in SD (Contd)

• Selection requires a second life line. One
  condition leads to the original life line and the
  other condition leads to the second one.

Dispenser
Front
Register
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Control in SD
Synchronous and asynchronous

• A synchronous message/signal is a control which
  has to wait for an answer before continuing.
  Hence, the sender passes the control to the
  receiver and cannot do anything until the
  receiver sends the control back.
• An asynchronous message is a control which does
  not need to wait before continuing. Hence, the
  sender actually does not pass the control to the
  receiver. The sender and the receiver carry on
  their work concurrently.

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Control in SD (Contd)

• Syntax
• Example the return item use case in the
  recycling machine.
• -- Concentrate on the rounded rectangle and
  answer the question Should getName and getValue
  be synchronous or asynchronous?

asynchronous
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Control in SD (Contd)
receipt
The customer presses the receipt button
printReceipt
print Logo, date
Print Logo and date, Find name and number for a
type of item, Find deposit value for a type of
item, Sum, Print sum
get value
value
get name
name
print
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Control in SD (Contd)
On one hand, getValue signal and getName signal
can be asynchronous as the system does not need
to wait for values before requesting name. On
the other hand, print message could be sent out
to the printer if getValue and getName were
asynchronous. For this reason, getValue signal
and getName signal must be synchronous.
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Control in SD (Contd)
receipt
The customer presses the receipt button
printReceipt
print Logo, date
Print Logo and date, Find name and number for a
type of item, Find deposit value for a type of
item, Sum, Print sum
get value
value
get name
name
print
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Control in SD (Contd)

• Concentrate on other signals and messages.
• -- receipt signal it does not even need a
  feedback. Therefore, it can asynchronous.
• -- printReceipt signal it can be asynchronous,
  too.
• -- printLogo, date message it can also be
  asynchronous, as no feedback is required.

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Control in SD (Contd)
receipt
The customer presses the receipt button
printReceipt
print Logo, date
Print Logo and date, Find name and number for a
type of item, Find deposit value for a type of
item, Sum, Print sum
get value
value
get name
name
print
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Recursion in SD

• Recursion or self-call -- an object/block may
  have an operation that invokes itself.
• Example (personal loan)

Year(0) loan(0) Year(1) loan(1) loan(0) ? (1
interestRate) Year(2) loan(2) loan(1) ? (1
interestRate) loan(0) ? (1
interestRate) ? (1 interestRate) Year(3)
loan(3) loan(2) ? (1 interestRate)
loan(1) ? (1 interestRate) ? (1
interestRate) loan(0) ? (1
interestRate) ? (1 interestRate)
? (1 interestRate)
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Recursion in SD

• Syntax

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Structure of SD

• Centralised structure -- Fork Everything is
  handled and controlled by the left-most block.

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Structure of SD (Contd)

• Decentralised structure -- Stair There is no
  central control block.