Systems Analysis and Design

SA&D Outline 9 Weeks of Lectures Supported by Tutorials Self Study Examples –Bushmouth –Lejk and Deeks

Expectations Minimum –Develop Accurate Data Flow Models –Develop Accurate Data Models –Apply Rules of Normalisation

Plan Introduction Structured Methods –Data Flow Modelling –Data Modelling –Relational Data Analysis –The Effect of Time Further Topics

Introduction to the Systems Development Life Cycle

Why a Development Lifecycle? “How to build an Information System” A means of controlling activities over time Plan that stops us forgetting something More likely to be delivered on time A straightjacket into which ALL development must fit? Remember We want to build this system and get it right!

Waterfall Model Feasibility Study System Analysis and Design Program and Unit Test System and Acceptance Test Operations Requirements Analysis Logical Design Technical Design (Whiteley, 2004)

Waterfall Model Proposed by Bennington (1956) –How to build large software systems –Needed highly structured approach Computers in 1956 Modified by Royce (1970) –New Requirement for Documentation –Large programs required Teams Computers in 1970

Lifecycle stages Feasibility – Is it possible Analysis – More detailed study Requirements Specification - deliverable Design – match with target architecture Implementation – Code / Installation Testing – For what? Maintenance - Operation

Feasibility A quick study of –Requirements –and possibilities Other constraints? Can it be done –For how much? –Deliverable – Yes/No decision

Feasibility It is possible that we will bin the idea! What are the consequences of insufficient detail?

Analysis Two major parts: –S–Study of the existing system –A–A more detailed look at the requirements –G–Gap analysis between existing and required system Deliverable – Requirements Specification –W–What we are going to do

Systems Analysis and Design Requirements Analysis Logical Design Technical Design

Requirements Specification A Major deliverable Describes what the new system will need to do –Will incorporate quality criteria –Will probably not deal with how it is to be done unless that is part of the quality criteria

Design In more detail –Process Design – Structured approach –Data Design – maintain integrity of data –Interface Design We know what data the user needs to see/enter How do we present it most effectively?

Design How do we fit what we need into our system architecture –3 tier client server architecture? –Web service oriented architecture? –Stand-alone database with VB front end? Algorithm design GUI design

Implementation Coding the designs Involves low level debugging and unit testing

Testing Some testing has already been carried out! What are we now testing for? How do we know it has passed the test? Can the system be sufficiently tested in the development environment? Do we need to run final tests during operation?

Maintenance Different types of maintenance –Corrective maintenance Probably part of the original contract Operating environment is significantly more complex that the development environment –Updates and Improvements Not necessary but adds value –Modification (due to changing requirements) Additional costs for user

Waterfall Model Feasibility Study System Analysis and Design Program and Unit Test System and Acceptance Test Operations

Timescales According to Mason and Willcocks (1994) –Feasibility Study5-10% –Analysis20-25% –Design20-25% –Code20-30% –Testing20-30%

Alternative 1 Analysis Design Code Test (Gane and Sarson, 1979)

Alternative 2 Project initiation Feasibility Investigation Requirements Definition Proposals and Selection Design Development Test Implementation Audit and Review Maintain (Yeates and Wakefield, 2004)

Alternative 3 – SSADM Stage 2 – Business System Options Stage 3 – Requirements Definition Stage 4 – Technical System OptionsStage 5 – Logical Design Stage 6 – Physical Design Stage 0 - Feasibility Stage 1 – Investigate Current System (Yeates and Wakefield, 2004)

Some Observations The number of stages will vary Issues for large systems projects –Long time for development/delivery –When are problems detected? –Good Documentation and audit trail Small Projects –Logical sequence of events –Doesn’t always reflect reality (who’s fault is this) –Large paper trail

SDLC So we should be able to agree that: –There are certain tasks that are required for all software/systems development projects –Systems Analysts should be familiar with all of them

Alternatives Why do we need alternatives –Project size –Exploratory programming/development –To make use of existing components (re-use) –Because requirements don’t freeze Need to match SDLC with business requirements and circumstances –E.g. McFarlan Strategic Grid

The Systems Analyst “…a skilled worker whose principle function is to design and implement computer based solutions to business problems…” (Mason and Wilcocks, 1994)

Systems Analyst Skills A problem discoverer A planner Focused A Listener Flexible Has a broad outlook Has sufficient understanding of the technology, and can talk sensibly with experts about it Orderly Methodical A good communicator with all sorts of people Has an eye for detail Has very good interpersonal skills A solution provider A team leader (often) Understands business and organisations Can use appropriate modelling techniques and development methodologies.

Some Modern Thinkers Our brain works iteratively not in a linear sequential manner (DeMarco, 1979) Top down development involves iterative refinements of a problem until a solution is found (Gane & Sarson, 1979) Design iterations are never confined to successive steps (Royce, 1970)

Structured Methods Existing System ERD Repository Existing Physical System DFD New System ERD Repository New Logical System DFD Convert to Logical View User Requirements Technical Options + Constraints New Physical System

Structured Methods Usually encompass the following techniques –Data Flow Model + Process Descriptions –Entity Relationship Model/Logical Data Structure –Entity Life Histories/State Transition Diagrams

Structured Methods Physical to Logical Transition –Considered an important stage But…according to Yourdon –“Why waste time modelling the current system when what we want is a new one?” (Yeates and Wakefield, 2004) (Lejk and Deeks, 2002)

Plan Introduction Structured Methods –Data Flow Modelling –Data Modelling –Relational Data Analysis –The Effect of Time Further Topics

References Whiteley, D. (2004) Introduction to Information Systems, Palgrave, Lejk, M. and D. Deeks (2002) Systems Analysis Techniques, Addison Wesley 2002 Mason, D. and L. Willcocks (1994), Systems Analysis, Systems Design, Alfred Waller, 1994.

References Yeates, D. and T. Wakefield (2004) Systems Analysis and Design, FT/Prentice Hall 2004 Gane, C. and T. Sarson (1979) Structured Systems Analysis, Prentice Hall, 1979 Eva, M (1994) SSADM Version 4: A users guide, McGraw hill, 1994 Yourdon, E. (1989) Modern Structured Analysis, Prentice Hall

References DeMarco, T. (1979) Structured Analysis and System Specification, Yourdon, 1979 Royce, W. (1970) Managing the development of large software systems, In: Proceedings of IEEE WESCON, 1970 pp1-9. Bennington, H. (1956) Production of Large Computer Programs In: Annals of the History of Computing, Vol. 5, No. 4, Oct 1983.