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

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).

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

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

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 Review Design Code

Alternative Approaches (4) Spiral model includes best features of both the classic Waterfall SDLC and the Prototyping approach. Planning Risk Analysis The Spiral Model - an iterative (evolutionary) system development life cycle developed by Boehm (1988) which incorporates risk assessment. Developed in recognition of the fact that systems development projects tend to repeat the stages of analysis, design and code as part of the prototyping process. Model closely related to RAD, as it implies iterative development with a review possible after each iteration or spiral - which corresponds to the production of one prototype or incremental version. Development Evaluation

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.

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

SDLC Stages and Deliverables (2) 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 Implementation:Code, Test & Install Maintain Review

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

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

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.

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).

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.

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.

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

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

Required Logical Design RequiredPhysical Design Design - Overview (3) Design Required Logical Design RequiredPhysical Design

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) 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.

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) 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.

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)

DESIGN Design Overview (9) Requirements Catalogue I/O Data Design Descriptions Data Design DESIGN Interface Design Program Design System Objectives: Review of Analysis, Requirements Specification, Design Objectives & Constraints. Data Design - Design of files and databases. I/O Design - Inputs & Output descriptions, Report & Form Design. Interface Design - Screen Design: Menus, Dialogues, etc. Process Design - Program design using structured English, etc. System Changeover Strategies - How to move from old to new system Documentation - System & User documentation. System changeover strategies Documentation: System & User

Physical and Logical Models Analysis Design Current Logical Required Logical Current Physical Required Physical