ACSC 155 System Analysis and Design 1 Introduction

ACSC 155 System Analysis and Design 1. Introduction Dr. Stephania Loizidou Himona 1

Information Systems What is a System? A system is a set of components that interact to accomplish some purpose Examples include the Economic system the Language system a Business and its parts e. g. Marketing, Sales, Research, Shipping, Accounting, Government etc. Dr. Stephania Loizidou Himona 2

INFORMATION SYSTEM What is an Information System (I. S. )? INFORMATION SYSTEM INPUT PROCESS OUTPUT FEEDBACK Dr. Stephania Loizidou Himona 3

§ Information System – Interrelated components working together to collect, process, store and disseminate information to support decision making, coordination control analysis and visualisation in an organisation. Dr. Stephania Loizidou Himona 4

§ Information versus Data § Basic components: – Input – Output – Processing – Feedback § Computer-based I. S. Dr. Stephania Loizidou Himona 5

What is Systems Analysis & Design? § The process of examining a (business) situation with the intent of improving it through better procedures and methods. Distinguish between: - System Analysis - Process of gathering and interpreting facts, diagnosing problems, and using the facts to improve the system. - Systems Design - Process of planning a new system to replace or complement the old. Dr. Stephania Loizidou Himona 6

§ Analysis specifies what the system should do; § Design states how to achieve the objective. Dr. Stephania Loizidou Himona 7

SYSTEM ANALYSIS OPORTUNITY TO IMPROVE A SYSTEM § A System development life cycle (SDLC) is a process by which systems analysts, software engineers, programmers, and end users build information systems and computer applications. It consists of 5 distinct stages. Dr. Stephania Loizidou Himona 8

Systems Life Cycle Dr. Stephania Loizidou Himona 9

1. Problem Identification What is the problem? Terms of Reference Preliminary Analysis (Feasibility Reports*) 2. System Analysis Priorization of the requirements for solving the problem. The emphasis is on the business, not the computer (what to do, not how to do it). Functional Specification Dr. Stephania Loizidou Himona 10

*Feasibility Study Advantages Vs Disadvantage § T § E § L § O § S Technical feasibility (technically practical, staff, expertise) Economic feasibility Is it cost effective? Law feasibility Is it legal? Operational feasibility Does it fulfill user requirements? To what degree? Will the work environment change? How does users feel about such a solution? Schedule feasibility Design and implementation in acceptable period of time? Dr. Stephania Loizidou Himona 11

3. System Design The evaluation of alternative problem solutions and the detailed specifications of the final solution computer-based. Emphasis shifts from the business to the computer solution (how to do it). Detailed Systems Specification Logical versus Physical Design. Dr. Stephania Loizidou Himona 12

4. System Implementation The construction or assembly of the new system and the delivery of that system into “production” (meaning “day-to-day” operation). Fully Documented system 5. System Support and Maintenance The ongoing maintenance and enhancement of a system after it has been placed into operation. This includes program maintenance and system improvements. Test Runs Dr. Stephania Loizidou Himona 13

§ Computer Assistant Software Engineering (CASE) Automated case tools Project Management tools and Techniques PERT CHART (Project Evaluation and Review Technique) Gantt Chart Dr. Stephania Loizidou Himona 14

USERS § § Direct Users (interact with the system) Indirect Users (initiate processes) Administrative Users (deal with money) People involved in Analysis – – Business Analysts (Identification, Feasibility, Analysis) Systems Designers (Design) Systems Analysts (Everything) Analyst Programmers (Everything, or what they know) § What do Systems Analysts do? § What skills so they need? Dr. Stephania Loizidou Himona 15

§ Objections to the life cycle model – Time scale factor – Difficult to be understood § An alternative approach – Design by Prototyping Dr. Stephania Loizidou Himona 16

Prototype § A live-working § Requirements specified in advance § An iterative process § Valuable at various stages of the SDLC Dr. Stephania Loizidou Himona 17

The prototype approach Dr. Stephania Loizidou Himona 18

Comparison of the SDLC and the Prototype Approaches SDLC Advantages Disadvantages Pre-defined stages (exactly what is required for each one) Takes too long time to complete requirements might change over time Guaranties effective end-result Needs computerised literate (expertise) people Experience in every step (consequence from 1 st advantage) The user sees only the end result Viscous circle (close loop – you are never finished with it) Costs too much Dr. Stephania Loizidou Himona 19

Prototype Advantages Disadvantages Live-working system. The user is actively involved User has to be able to criticise/suggest the system computerised expertise Interactive (you actually see stages of it, and not only the end result suggest alternatives as you go along – test its operation No pre-defined stages Iterative (things happening in loops) Does not guarantee an effective end result (incomplete working system) Can be used as a first attempt of a design It cannot handle big systems Library search for an ‘existing – similar’ system Cost Dr. Stephania Loizidou Himona 20