Asper School of Business University of Manitoba

Systems Analysis & Design

Instructor: Bob Travica

System sequence diagram

Updated: 2017

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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

SSD of a customer order system

Figure 6-14

Content of Item: item details

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Global SSD – loops

Figure 6-15

True/FalseCondition

Input

Expected output

Loop

Note: extendedPrice = price * quantity

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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.)

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

AccountaccountNocustomerID

ProductproductID

size description

CatalogcatalogI

D

CatalogProduct price

OrderorderIDaccountNoTotalAmt

OrderDetail

quantityextendedPrice

places

contains

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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)

Control handler object

Domain objects (replace :System)

Activation lifeline

Figure 8-14SSD for Look Up ItemAvailabilityuse case

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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.

Additional objects

Figure 8-1

3. Store database object (record)

4. Update Student record

5. Update Student object

6. Store the update

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Detailed SSD (final) - reading

Reading: Specific catalog and inventory objects are initialized by user’s input, and it will get data from the corresponding database objects.

Figure 8-17: Final SSD for the use caseLook Up Item Availability(product description, price, quantity in inventory)

User Interface Database (DA=Data Access Layer)