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Systems Analysis and Design
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SA&D Outline
• 9 Weeks of Lectures
• Supported by Tutorials
• Self Study Examples– Bushmouth– Lejk and Deeks
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Expectations
• Minimum– Develop Accurate Data Flow Models– Develop Accurate Data Models– Apply Rules of Normalisation
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Plan
• Introduction
• Structured Methods– Data Flow Modelling– Data Modelling– Relational Data Analysis– The Effect of Time
• Further Topics
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Introduction to theSystems Development Life Cycle
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Why a Development Lifecycle?
“How to build an Information System”A means of controlling activities over time
Plan that stops us forgetting somethingMore likely to be delivered on time
A straightjacket into which ALL development must fit?
RememberWe want to build this system and get it right!
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Waterfall Model
FeasibilityStudy
System Analysisand Design
Program andUnit Test
System andAcceptance Test
Operations
RequirementsAnalysis
LogicalDesign
TechnicalDesign
(Whiteley, 2004)
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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
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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
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Feasibility
• A quick study of– Requirements – and possibilities
• Other constraints?
• Can it be done– For how much?– Deliverable – Yes/No decision
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Feasibility
• It is possible that we will bin the idea!
• What are the consequences of insufficient detail?
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Analysis
• Two major parts:– Study of the existing system– A more detailed look at the requirements– Gap analysis between existing and required
system
• Deliverable – Requirements Specification– What we are going to do
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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
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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?
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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
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Implementation
• Coding the designs
• Involves low level debugging and unit testing
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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?
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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
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Waterfall Model
FeasibilityStudy
System Analysisand Design
Program andUnit Test
System andAcceptance Test
Operations
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Timescales
• According to Mason and Willcocks (1994)– Feasibility Study 5-10%– Analysis 20-25%– Design 20-25%– Code 20-30%– Testing 20-30%
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Alternative 1
• Analysis
• Design
• Code
• Test
(Gane and Sarson, 1979)
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Alternative 2
• Project initiation• Feasibility• Investigation• Requirements Definition• Proposals and Selection• Design• Development• Test• Implementation• Audit and Review• Maintain
(Yeates and Wakefield, 2004)
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Alternative 3 – SSADM
Stage 2 – Business System Options
Stage 3 – Requirements Definition
Stage 4 – Technical System Options Stage 5 – Logical Design
Stage 6 – Physical Design
Stage 0 - Feasibility
Stage 1 – Investigate Current System
(Yeates and Wakefield, 2004)
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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
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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
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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
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The Systems Analyst
• “…a skilled worker whose principle function is to design and implement computer based solutions to business problems…”
(Mason and Wilcocks, 1994)
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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.
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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)
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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
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Structured Methods
• Usually encompass the following techniques– Data Flow Model + Process Descriptions– Entity Relationship Model/Logical Data
Structure– Entity Life Histories/State Transition Diagrams
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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)
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Plan
• Introduction
• Structured Methods– Data Flow Modelling– Data Modelling– Relational Data Analysis– The Effect of Time
• Further Topics
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References
• Whiteley, D. (2004) Introduction to Information Systems, Palgrave, 2004.
• 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.
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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
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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.