Systems Analysis

What is it?

2

A Systems Development Life Cycle• The need for change is recognised or planned for• Outline requirements may be issued, with some

idea of the investigation scope, resources etc

- Terms of Reference• Feasibility issues may be considered, especially

for ‘high risk’ developments• Detailed Systems Analysis occurs• A proposed System Design is produced• The Systems Specification is developed into an

Implementation• There is a period of Evaluation & Review

Ref: D. Bishton

3

Systems Analysts – agents of change• Investigate an Organisation’s Information Systems

requirements

• They consider the effect of its Environment on an Organisation’s activities (Processes, Functions)

• They consider the feasibility and impact – financial, technological & social, of recommended changes to an organisation’s Processes, Data & Organisational Structures

• They model Behaviour, Process and Data Structures to support the development of an Organisation’s Information Systems, whether automated or manual

• They help to understand, (re)organise, synthesise and communicate appropriate Data Structures and Processes for an Organisation’s use

Ref: D. Bishton

Fact-finding

1. Use a variety of techniques to gather knowledge about the system

2. Analyse those facts to remove ambiguity, identify omissions, resolve conflicts.

– Use different perspectives/viewpoints to identify these problems

Logical Information Model

• What data does the information system need (to handle, to store)?

• Define terminology• Define meaning• Define data structure

1. Data Dictionary definitions

2. Logical Data Structure diagram:

Project Partuses

used by

Supplier

Supplies

Supplied by

Process Model

• Where is the system boundary?

• What processes does the system need to carry out?

• What data is input to and output from each process?

1. Data Flow Diagrams (including Context Diagram)

2. Elementary Process Descriptions

Event Model

• How do events in the real world trigger changes in the Information system?

• What information in the system changes then?

• In what order do things need to happen?

1. Entity Life History

Bank Account

Acct Opened

- / 11 6 7

Acct Life

Transaction

Cash Dep

1/1 2/1 2/22 8

Cash W/D

1/1 1/23 8

Acct Closure

1/34

Acct Deletion

3/-5

OPERATION LIST

1: STORE Bank Account2: SET Balance [Bank Account.] OF Bank Account := Balance + Cash Deposit

3: SET Balance [Bank Account.] OF Bank Account := Balance - Cash Withdrawal4: SET Status [Bank Account.] OF Bank Account := 'Closed'

5: CUT Bank Account FROM Customer6: SET Balance [Bank Account.] OF Bank Account := Initial Deposit

7: SET Status [Bank Account.] OF Bank Account := 'In credit'8: SET Status [Bank Account.] OF Bank Account := 'In credit' if balance >0 or 'In debt' if balance <0

State Indicators

1 = In credit2 = In debt3 = Closed

Summary

• Systems Analysis takes the facts found and “analyses”/considers them

• Identifies WHAT the information system must do

• Business point of view – no consideration of technology architecture

• Lateral/creative thinking needed

References(from recommended texts)

• Kendall & Kendall, chapters 1, 4, 5• Whitten & Bentley, chapters 1-4• Denis & Wixom, chapters 4-5