CP2236: Information Systems Design
Information Systems Development (ISD)
Systems Development Life Cycle
Overview of Analysis Phase
Overview of Design Phase
Information Systems Development
A logical series of development phases
followed in an organisation to conduct all
the steps necessary to analyse, design,
implement & maintain information systems.
These logical series of development phases
- known as System Development Life Cycle
Systems Development Life Cycle (SDLC)
Scope & objectives
•Waterfall Model Design
– Proven approach Implement
– Lacks flexibility
– Time lag
– Ensures points of review
Alternative Approaches (1)
• Waterfall SDLC with iterations:
Scope & objectives
Alternative Approaches (2)
• Beer mat and hack.
• Prototyping / Rapid Application Development.
– Uses a different SDLC
– System developed in smaller units
– Iterative Analysis
– Less time lag
– User participation Review Design
Alternative Approaches (4)
Spiral model includes best features of both the classic
Waterfall SDLC and the Prototyping approach.
Alternative Approaches (5)
Each spiral consists of four main activities:
• Planning: setting project objectives; defining
alternatives; further planning on the next spiral; etc.
• Risk Analysis: analysis of alternatives & the
identification & solution of risks.
• Development: designing, coding and testing etc. in
• Evaluation: user evaluation of each spiral and then the
SDLC Stages and Deliverables (1)
Scope & Objectives Terms of Reference
Analysis Physical & Logical models
Logical models of required
Design system, physical design and
detailed design documentation
SDLC Stages and Deliverables (2)
Code - program
Code, Test & Test - Test plans from unit to
Install system & acceptance testing
Install - system changeover,
installation of hw/sw, user &
system documentation and
Maintain Maintenance procedures
Review Evaluation report
Analysis - Overview (1)
Scope & Objectives PRL RC
Feasibility current system’s
Time Implement Process desc.
Analysis - Overview (2)
System Data Store Entity Logical
LDS Cross Reference DFDs
Analysis - Overview (3)
• Analysis - gathering & documentation of information
about the current system & the required system.
• To achieve this - a number of techniques are used.
– Problem Requirement List feeds into Requirements
Catalogue: contain information about current
problems & future requirements
(logical: functional & physical: non-functional)
– Data Flow Diagrams (Processing): contain
information about the processing, inputs and
outputs and data stores to be accessed. 12
Analysis - Overview (4)
– Logical Data Structures (Data): contain
information about the groups of data (entities) and
– Input\Output Descriptions: contain information
about data that flows into and out of the system.
– Process Descriptions: contain information about
how the processes actually work & these can be
specified using various techniques
(e.g. Structured English, Decision Tables &
Analysis - Physical & Logical
• Physical analysis includes all physical aspects
– e.g. Filing cabinets, Locations, (Who, When,
• Physical analysis become logical when all the
physical aspects are removed by logicalisation.
– Therefore there are 2 versions of the DFDs current
physical and current logical.
Analysis - Data & Processing
• DFDs model information about the processing
in the current system.
• LDS models information about the data in the
• Data & Processing are two separate but
essential components of an Information System.
Analysis - Techniques
• The techniques used to perform analysis are
taken from Structured Systems Analysis and
Design Methodology (SSADM).
• There are other techniques and ways of
combining them in order to perform analysis.
Design - Overview (1)
Scope & Objectives
Design - Overview (2)
PRL RC Requirements
current system’s Specification
DFDs of req. System
Process desc. Design
of req. System 18
Design - Overview (3)
Design Design 19
Design - Overview (4)
Logical Design: gives a detailed logical
definition of the required system.
Physical Design: takes the products of the
logical design and produces specifications
for the target hardware and software.
Design - Overview (5)
•No reference made to any technical
•Capable of implementation on a variety of
•Act as a model of how the system will
satisfy the user requirements.
•Reflect underlying business rules &
activities rather than physical constraints.
Design - Overview (6)
Logical Design - blueprint is the delivered
product of the required system.
It includes the following:
• Requirements Catalogue
• Required system DFDs
• Required system LDS
• Relational Data Analysis (normalised set
of tables and rationalised set of tables)
Design - Overview (7)
•Logical design translated into a physical
design based on the technical environment
selected, e.g. platform, programming
language, database etc.
•Produces program specifications, physical
files or database definitions and user
interfaces for a selected target hardware &
Design - Overview (8)
Physical design includes contents of the
• Data design - (requirements for data to be
stored in a database)
• Outputs design - (reports, displays)
• Inputs design - (forms, screens, dialogues)
• Programs design - (structure of programs to
collect, transform & output data)
Design Overview (9)
Interface Program Design
System & User
Physical and Logical Models