1 Information Systems Development (ISD) Systems Development Life Cycle Overview of Analysis Phase Overview of Design Phase CP2236: Information Systems Design

2 Information Systems Development (ISD) 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 (SDLC).

3 Systems Development Life Cycle (SDLC) Waterfall Model – Proven approach – Lacks flexibility – Time lag – Ensures points of review Feasibility Analysis Design Implement Maintain Review Time Scope & objectives

4 Feasibility Analysis Design Maintain Review Alternative Approaches (1) Waterfall SDLC with iterations: Implement Scope & objectives

5 Alternative Approaches (2) Beer mat and hack. Prototyping / Rapid Application Development. –Uses a different SDLC –System developed in smaller units –Iterative –Less time lag –User participation Analysis Design Code Review

6 Alternative Approaches (4) Spiral model includes best features of both the classic Waterfall SDLC and the Prototyping approach. Planning Risk Analysis Development Evaluation

7 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 increments. Evaluation: user evaluation of each spiral and then the final product.

8 SDLC Stages and Deliverables (1) Feasibility Scope & Objectives Analysis Design Terms of Reference Feasibility Report Requirement specification, Physical & Logical models Logical models of required system, physical design and detailed design documentation

9 Implementation: Code, Test & Install Maintain Review Code - program documentation Test - Test plans from unit to system & acceptance testing Install - system changeover, installation of hw/sw, user & system documentation and training Maintenance procedures Evaluation report SDLC Stages and Deliverables (2)

10 Analysis - Overview (1) Feasibility Design Maintain Review Time PRL RC current system’s DFDs LDS I/Os Process desc. Requirements Specification of req.System Analysis Implement Scope & Objectives

11 Analysis - Overview (2) Current Physical DFDs Current Logical DFDs Current System LDS Problem Requirements List (Requirements Catalogue) Logicalisation Data Store Entity Cross Reference PHYSICAL ANALYSIS LOGICAL ANALYSIS

12 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. Analysis - Overview (3)

13 Analysis - Overview (4) –Logical Data Structures (Data): contain information about the groups of data (entities) and their relationships. –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 & Decision Trees).

14 Analysis - Physical & Logical Physical analysis includes all physical aspects –e.g. Filing cabinets, Locations, (Who, When, Where, etc). 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.

15 Analysis - Data & Processing DFDs model information about the processing in the current system. LDS models information about the data in the current system. Data & Processing are two separate but essential components of an Information System.

16 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.

17 Design - Overview (1) Feasibility Analysis Maintain Review Time Design Implement Scope & Objectives

18 Design - Overview (2) Design Requirements Specification of req. System PRL RC current system’s DFDs LDS I/Os Process desc. System Specification of req. System

19 Design - Overview (3) Design Required Physical Design Required Logical Design

20 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.

21 Design - Overview (5) Logical Design: No reference made to any technical environment. Capable of implementation on a variety of platforms. Act as a model of how the system will satisfy the user requirements. Reflect underlying business rules & activities rather than physical constraints.

22 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)

23 Design - Overview (7) Physical Design: 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 & software.

24 Design - Overview (8) Physical design includes contents of the following components; 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)

25 Design Overview (9) DESIGN I/O Descriptions Interface Design Data Design Program Design System changeover strategies Documentation: System & User Requirements Catalogue

26 Physical and Logical Models Current Physical Current Logical Required Logical Required Physical AnalysisDesign