Asper School of Business
University of Manitoba
Systems Analysis & Design
Instructor: Bob Travica
System sequence diagram
Updated: 2014
Outline
Concept of SSD
 Global SSD
 Creating global SSD
 Detailed SSD (reading)

First cut
 Full

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Concept of System Sequence
Diagram (SSD)

Part of system design. Communicates to
OO programmers.

SSD shows interaction between actors
and system (global SSD), and among
objects (detailed SSD)

SSD specifies flow of data (messages)

Messages are actions (resemble
commands) invoked on destination
object
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Global SSD
Figure 6-14
item details
Content of Item:
SSD of a customer order system
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Global SSD – loops
Figure 6-15
Note: extendedPrice =
price * quantity
Expected output
True/False
Condition
Loop
Input
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Creating global SSD
1. Start with an activity diagram and/or use case
description.
2. Identify the input messages from actor to system.
For figuring attributes (input parameters), use
class diagram.
3. Identify/apply special conditions (iteration) to
input messages, if any.
4. Identify output messages.
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Creating global SSD
(cont.)
Account
accountNo
customerID
OrderDetail
quantity
extendedPrice
places
Order
orderID
contains
accountNo
TotalAmt
Product
productID
size
description
CatalogProduct
price
Catalog
catalogID
Figure 6-16. Activity diagram of
Create New Order use case,
Telephone Scenario at RMO
Figure 6-17. Global SSD of the same
Figure 5-31 (detail).
Class diagram of RMO
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Detailed SSD

Uses the same elements as an SSD

Has extra elements:

The :System object is replaced by objects and
messages within computer system

Objects are differentiated (e.g., control handler,
domain, user interface)

Object activation period indicated
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Detailed SSD for Look Up Item Availability first cut (actor and domain classes)
Figure 8-14
SSD for
Look Up Item
Availability
use case
Control handler
object
Domain objects (replace :System)
Activation
lifeline
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Reading detailed SSD (first cut)

The system object is broken down to specific
objects.

Inputs & outputs among objects are specified.
Class diagram essential (follow associations).
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Adding user interface
and database to SSD
• Add user interface and database objects to domain
objects. Example function: Create new student.
Figure 8-1
3. Store database
object (record)
6. Store update
5. Update Student
object
4. Update Student
record
Additional
objects
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Detailed SSD (final) - reading
User Interface
Database (DA=Data Access Layer)
Figure 8-17: Final SSD
for the use case
Look Up Item Availability
(product description,
price, quantity in
inventory)
Reading: Specific catalog and inventory objects are
initialized by user’s input, and it will get data from the
corresponding database objects.
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