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