Lecture 2
System Development Lifecycles
Building a house Definition phase Analysis phase Design phase Programming phase System Test phase Acceptance phase Operation phase
Lifecycles System Development Lifecycles
covers the whole life of a system technical products
Project Lifecycles delivery of a specified product technical products, quality products,
management products
Development Lifecycle Models Waterfall Model
“b” Model “V” Model Incremental Model Traditional Approach Structured Method
SSADM Spiral Model
Waterfall Model Feature
a number of sequential stages a degree of iteration of work and
products within a stage very little iteration between stages rework is carried in succeeding stages
Waterfall Model Advantage
sequencing of activities quality management
verification validation
configuration management
Waterfall Model Disadvantage
planning, control and risk management are not covered
Application requirements are well understood not likely to undergo significant
business change
“ b” Model Feature
variation of the waterfall model it takes its name from its distinctive “b”
shape maintenance and enhancement shown as a
series of cycles each of which follows the same general sequence as the original development
Advantage maintenance phase is adequately covered
“ V” Model Feature
variation of the waterfall model the successive stages are shown in a
“V” format shows correspondence between the
different stages of the project
“ V” Model Advantage
demonstrates elements of quality assurance in its treatment of the correspondence
Application development work being provided by
external contracts
Incremental Model Feature
variation of waterfall model phased delivery
Advantage delivery and testing more
manageable allowing familiarization with the
changes
Incremental Model Disadvantage
difficult to break the delivery of system down into phases
introduce overheads of integration Application
total scope and definition of requirements must be completed before the increments are defined.
Spiral Model Feature
an evolutionary or iterative approach to systems development
project starts at the center of the spiral and progress outwards
at the center, the requirements will be poorly understood and will be successively refined with each rotation around the spiral
Spiral Model the total cost of the project will
increase as the length of the spiral increases
four quadrants top left quadrant top right quadrant bottom right quadrant bottom left quadrant
Spiral Model Advantage
objective setting, risk management & planning
Application requirements are not well formed or
understood by the users difficult to specify the requirements difficult to determine how a proposed
solution will perform in practice
Traditional Approach Feature
unstructured and non-specific variations of the waterfall model
Advantage analyst can use “intuitive” methods of
working limited demands on the user’s time documentation was relatively easy to
understand, being mostly in English
Traditional Approach Disadvantage
lack of user involvement poor quality abdication of responsibility by the users
and blame for the developers use of text-based
ambiguous and misunderstanding emphasis on how rather than what
Structured Methods Feature
have largely taken over the traditional approach in the development of IS projects
offer a set of techniques and tools to carry out the systems development work within a defined framework
Structured Methods Advantage
user involvement separation of logical and physical emphasis on data diagrammatic documentation defined structure
Structured Methods Disadvantage
users and analysts/developers need to be trained to understand the documentation
amount of time required from users will be much increased
lead to increased level of documentation and therefore of bureaucracy
disastrous to assume that the method, rather than the analyst, will do the work
SSADM Structured Systems Analysis and Design
Method Three basic views of an information
system what information is stored and how it is
interrelated Logical Data Structure
how information is passed around Data Flow Diagrams
how information is changed during its lifetime Entity Life Histories
SSADM Combines techniques into a well-
established framework, provide alternative views of a system that cross-check each other to ensure that an accurate and complete picture of the system is formed
Overview of SSADM Information systems planning
strategic planning for the development of future and existing information systems
partial SSADM support Project Initiation
project is set up, terms of reference agreed, team members assigned, and plans drawn up
full SSADM support
Overview of SSADM Feasibility study
decided whether project is technically possible, whether it can be financially and socially justified, and whether the new system will be accepted by the organization
full SSADM support
Overview of SSADM Systems analysis
Analyze the current system and determine the requirements for a new system
full SSADM support Business systems design
Detailed logical design of the new system is developed in a non-technical way
full SSADM support
Overview of SSADM Physical design
convert logical design to physical design that fits the computer hardware and software selected
full SSADM support Construction
programming, the assembly of programs into a system and testing
partial SSADM support
Overview of SSADM Transition
transition from operating the old system to operating the new
partial SSADM support Production
completely handed over to the users no SSADM support
Overview of SSADM Maintenance and review
correction of errors, adaptation to new software and hardware releases, and minor enhancements
Partial SSADM support
Principles of SSADM Structures
define the frameworks of steps and stages and their inputs and outputs
stage 1 : analysis of system operations and current problems
stage 2 : specification of requirements stage 3 : selection of technical options stage 4 : logical data design stage 5 : logical process design stage 6 : physical design
Principles of SSADM Techniques
define how the steps and tasks are performed
diagrammatic techniques Data Flow Diagrams Logical Data Structures Entity Life Histories Logical Dialogue Design
Principles of SSADM non-diagrammatic techniques
relational data analysis first cut rules physical design control quality assurance project estimating
Principles of SSADM Documentation
defines how the products of the steps are presented
documents diagrams forms matrices narrative reports
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