CP 2236 Information Systems Design Information Systems Development

CP 2236: Information Systems Design Information Systems Development (ISD) Systems Development Life Cycle Overview of Analysis Phase Overview of Design Phase 1

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). 2

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

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

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 Code 5

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

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. 7

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

SDLC Stages and Deliverables (2) 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 9

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

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

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 their relationships. – InputOutput 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). 13

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. 14

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. 15

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. 16

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

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

Design - Overview (3) Design Required Logical Design Required Physical 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. 20

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. 21

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) 22

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. 23

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) 24

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

Physical and Logical Models Analysis Design Current Logical Required Logical Current Physical Required Physical 26