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- 1. Structured Systems Analysis and Design COURSE INSTRUCTOR: Mr. Abdul-rahim H. Ali The State University Of Zanzibar 1 CS/INF 1211:SYSTEM ANALYSIS AND DESIGN
- 2. Structured Systems Analysis and Design (Traditional Approach) • Is a systems approach to the analysis and design of information systems • It adopts a formal step-by-step approach to the SDLC phases and activities • The activities of one phase must be completed before moving to the next phase • At the completion of each activity or phase, a document is produced that must be approved by the stakeholders before moving to the next activity or phase. • This is necessary as teams of developers with varying skills and responsibilities 2
- 3. Traditional Approach(structured approach) • The center of the structured approach is the process model, which depicts the business processes of a system, and the primary model that presents the processes is the data-flow diagram (DFD) • It involves two major phases – systems analysis: defining what has to be done –System design: defining how it will be done 3
- 4. 4 The Analysis stages • The objective of analysis is to create a detailed specification of user requirements and to agree with users the level of service and performance required: • The stages are: Analysis of systems operations and current problems Specification of requirements, in terms of what the system must provide rather than how it will work Selection of technical options, in which the user selects a system for implementation from a list of possibilities, each having different service levels, costs/benefits, and development implications
- 5. 5 The Design stages • The objective of systems design is to define the system to provide the required services, and formulate a plan of how it is to be implemented: The stages are: Data design, in which the detailed logical data structure and content is defined Physical design, in which conversion of the logical design to one for implementation on a particular hardware and software environment is specified and refined to meet performance requirements
- 6. 6 Why use a structured method? • They structure a project into small, well defined activities and specify the sequence and interaction of these activities • They use diagrammatic and other modelling techniques to give a precise (structured) definition that is understandable by both users and developers
- 7. 7 Structured systems Analysis and Design • It involves the application of a sequence of analysis, documentation, and design tasks concerned with the following Stage 0: Feasibility analysis Stage 1: Investigation of current Environment Stage 2: Business System Options Stage3: Requirement Specification Stage 4: Technical System Options Stage 5: Logical Design (data and process design) Stage 6: Physical Design
- 8. 8 Stage 0: Feasibility analysis • Is to determine whether or not a given project is feasible, especially for large projects • When a feasibility study is conducted , there are areas of consideration Technical: is project technically feasible? Financial: can the business afford to carry out the project? Organizational: will the new system be compatible with existing practices? Economical: is the benefit of the new system outweigh the cost? Ethical: is the impact of the new system socially acceptable? • To answer these questions, the feasibility study is conducted to come up with a formal feasibility study document
- 9. 9 Stage 1: Investigation of current Environment • It involves analysis of systems operations and current problems • Though tasks and objectives of a new system may be radically different from the old system, the underlying data will probably change very little • Full understanding of the data and process requirements at early stage of project required through Interviewing Circulating questionnaires Observations Existing documentation
- 10. 10 Stage 1: Investigation of current Environment • These Techniques serve many purposes The analyst learns the terminology of the business, what users do and how they do it The old system provides the core requirements for the new system Faults, errors and areas of inefficiency are highlighted and their correction added to the requirements The data model can be constructed The boundaries of the system can be defined
- 11. 11 Stage 1: Investigation of current Environment • The product of this stage are: Users Catalog describing all the users of the system and how they interact with each other Requirements Catalog detailing all the requirements of the new system Current Service Description Current System Logical DFD Context Diagram DFD Leveled set of DFD for current local system Full data Dictionary including relationship between data stores and entities Current Physical DFDs with full details of how the old system is implemented
- 12. 12 Stage 2: Business System Options • Having Investigated the current system, the analyst must decide on the overall design of the new system • Using the outputs of the previous stage, develop a set of business system options • The options considers the following The degree of automation The boundary between the system and users The distribution of the system, for example, is it centralized to one office or spread out across several? Cost/Benefit Impact of the new system
- 13. 13 Stage 2: Business System Options • The analyst may hold a brainstorming session so that as many and variuos ideas as possible are generated • The analyst and users together choose a single business option • The output of this stage is the single selected option together with all the output of the feasibility stage
- 14. 14 Stage 3: Requirement Specification • It is probably the most complex stage • Using the requirements developed in stage 1 and working within the framework of the selected business option, develop a full logical specification of what the new system must do • By logical here means that the specification does not say how the system will be implemented but rather describes what the system will do • To produce the logical specification, build the required logical models for both the DFDs and ERDs
- 15. 15 Stage 3: Requirement Specification • The product of this stage is a complete requirement specification and is made up of: The updated data catalog The updated requirements catalog The processing specification User role and function matrix Function definitions Required logical data model Entity life histories Effective correspondence diagrams
- 16. 16 Stage 4: Technical System Options • This is the first step towards a physical implementation of the new system • Like the business system options, in this stage a large number of options for the implementation of the new system are generated The hardware architecture The software to use The cost of implementation The staffing required The physical limitations such as a space occupied by the system The distribution including any networks which that may require The overall format of the computer Interface • All of these aspects must also conform to any constraints imposed by the business such as available money and standardization of hardware and software • The output of this stage is a chosen technical system option
- 17. 17 Stage 5: Logical Design • Though the previous stages specifies details of implementation, the output of this stage are implementation-independent and concentrate on the requirements for the human computer interface • It specifies the main methods of interaction in terms of menu structures and command structures • Analyzing the effects of events in updating the system • The product of this stage is the logical design which is made up of Data catalog Required data logical structure-includes dialogue and model for the update and inquiry process Logical process model
- 18. 18 Stage 6: Physical Design • The final stage where all the logical specifications of the system are converted to descriptions of the system in terms of real hardware and software • The logical data structure is converted into a physical architecture in terms of database structures. The exact structure of the functions and how they are implemented is specified • The physical data structure is optimized where necessary to meet size and performance requirements • The product is a complete physical design which could tell software engineers how to build the system in specific details of hardware and software and to the appropriate standard
- 19. 19 END!