appendix_b - APPENDIX B System Design Tto create aphase of...

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T he design phase of the SDLC uses the requirements that were gathered during analy- sis to create a blueprint for the future system. A successful design builds on what was learned in earlier phases and leads to a smooth implementation by creating a clear, accu- rate plan of what needs to be done. This chapter describes the initial transition from analysis to design and presents three ways to approach the design for the new system. OBJECTIVES Understand the initial transition from analysis to design. Understand how to create a system speciFcation. Be familiar with the custom, packaged, and outsource design alternatives. Be able to create an alternative matrix. Be able to create physical data ±ow diagrams and entity relationship diagrams. Be able to create a CRUD matrix. CHAPTER OUTLINE INTRODUCTION The purpose of the analysis phase is to Fgure out what the business needs. The purpose of the design phase is to decide how to build it. During the initial part of design, the project team converts the business requirements for the system into system requirements that describe the technical details for building the system. Unlike business requirements, which are listed in the requirements deFnition and communicated through use cases and logical process and data models, system requirements are communicated using a collection of Introduction Design Strategies Custom Development Packaged Software Outsourcing Design Strategy Business need In-house Experience Project Skills Project Management Time ²rame Selecting a Design Strategy Alternative Matrix Applying the Concepts at CD Selections Moving from Logical to Physical Models The Physical Data ²low Diagram Applying the Concepts at CD Selections The Physical Entity Relationship Diagram CRUD Matrix Summary APPENDIX B System Design 1
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design documents and physical process and data models. Together, the design documents and physical models comprise the blueprint for the new system. The design phase has a number of steps that lead to the system blueprint (see Figure B-1). An important initial part of the design phase is the examination of several design strategies to decide which will be used to build the system. Systems can be built from scratch, purchased and customized, or outsourced to others, and the project team needs to investigate the viability of each alternative. The decision to make, to buy, or to outsource in±uences the design tasks that are performed throughout the rest of the phase. Next, the project team converts the logical diagrams that show the functional business requirements into physical diagrams that explain how to build the system. The logical DFDs and ERDs are converted into physical DFDs and ERDs, and CASE repository entries are expanded to include much more detailed information about how components of the diagrams map to speci²c technology. To ensure that the DFDs and ERDs balance properly, analysts create a CRUD matrix to show the way in which data is used by the system’s processes. In some situations, the logical use cases may also need to be revised, but this is
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appendix_b - APPENDIX B System Design Tto create aphase of...

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