INF 3703databases-2-inf3703-summaries. BEST DOCUMENT FOR EXAM

Chapter 9 Database Design 9-1 The Information System [p.440] A database is a carefully designed and constructed repository of facts. The database is part of a large whole known as an Information System, which provides for data collection, storage, transformation, and retrieval. Systems analysis is the process that establishes the need for an information system and its extent. The process of creating an information system is known as systems development. The performance of an information system depends on three factors: 1. Database design and implementation 2. Application design and implementation 3. Administrative procedures The term database development describes the process of database design and implementation. The primary objective in database design is to create completer, normalized, nonredundant and fully integrated conceptual, logical and physical models. 9-2 The Systems Development Life Cycle (SDLC) [p.442] The SDLC traces the history of an information system. 9-2a Planning [p.442] An initial assessment of the information flow and extend requirement must be made during this discovery portion of the SDLC. Such an assessment should answer some important questions: - Should the existing system be continued? If the information generator does its job well, there is no point in modifying or replacing it. - Should the existing system be modified? If the initial assessment indicates deficiencies in the extent and flow of the information, minor( or major) modification might be needed. - Should the existing system be replaced? The initial assessment might indicate that the current system’s flaws are beyond fixing. The feasibility study must address the following: - The technical aspects of hardware and software requirements - The decision might not yet be vendor-specific, but must address the nature of the hardware requirements and the software requirements. - The system cost - The admittedly mundane question “can we afford it?” is crucial. The answer might force a careful review of the initial assessment. At some point, the decision may be between building a system “in house” or buying a 3rd party vendor system. - The operational Cost - Does the company possess the human, technical and financial resources to keep the system operational? What would the impact of this new system be? Downloaded by Nolwandle Mnisi () lOMoARcPSD| 9-2b Analysis [p.443] Problems defined during the planning phase are examined in greater detail during the analysis phase. A macro analysis must be made both of individual needs and organizational needs, addressing questions such as: - What are the requirements of the current system’s end user? - Do those requirements fit into the overall information requirements? The analysis phase is, in effect, a thorough audit of user requirements. When creating logical design, the designer might use tools such as data flow diagrams (DFDs), hierarchical input process output (HIPO) diagrams, entity relationship (ER) diagrams and even some application prototypes. 9-2c Detailed Systems Design [p.444] The designer completes the design of the new system’s processes. The design includes all the necessary technical specifications for the screens, menus, reports, and other devices that might help make the system a more efficient information generator. 9-2d Implementation [p.444] During the implementation phase, the hardware, DBMS software, and application programs are installed and the database design is implemented. The database contents might be loaded interactively or in batch mode, using a variety of method and devices: - Customized user programs - Database interface programs - Conversion programs that import the data from a different file structure, using batch programs, a database utility, or both The system is in full operation at the end of this phase, but it will be continuously evaluated and fine-tuned. 9-2e Maintenance [p.445] Almost as soon as the system is operations, end users begin to request changes in it. Those changes generate system maintenance activities, which can be grouped into three types: - Corrective maintenance - in response to system errors - Adaptive maintenance - Due to changes in the business environment - Perfective maintenance - To enhance the system If the system’s maintenance cost is high, its value becomes suspect. Computer aided software engineering (CASE) tools, help produce better systems within a reasonable amount of time and at a reasonable cost. 9-3 The Database Life Cycle (DBLC) [p.445] 9-3a The Database Initial Study [p.445] In addition to examining the current system’s operation within the company, the designer must determine how and why the current system fails. Downloaded by Nolwandle Mnisi () lOMoARcPSD| The overall purpose of the database initial study is to: - Analyze the company situation - Define problems and constraints - Define objectives - Define scope and boundaries 1. Analyze the company Situation The company situation describes the general conditions in which a company operates, its organizational structure, and its mission. The following issues must be resolved: - What is the organization’s general operating environment, and what is its mission within that environment? The design must satisfy the operational demands created by the organization’s mission. - What is the organization's structure? Knowing who controls what and who reports to whom is quite useful when you need to define required information flows, specific report and query formats, and so on. 2. Define Problems and Constraints The designer has both formal and informal sources of information. The problems might initially appear to be unstructured. End users often cannot precisely describe the larger scope of company operations. Often managers’ views are different from that of the end users. During the initial problem definition process, the designer is likely to collect very broad problem descriptions. After the initial declarations, the database designer must continue to probe carefully to generate additional information that will help define the problems within the larger framework of company operations. 3. Define Objectives A proposed database system must be designed to help solve at least the major problems identified during the problem discovery phase. The database designer must begin to address the following questions: - What is the proposed system’s initial objective? - Will the system interface with other existing or future systems in the company? - Will the system share the data with other systems or users? 4. Define Scope and Boundaries The designer must be recognize two sets of limits: scope and boundaries. The system’s scope defines the extent of the design according to operational requirements. Will the database design encompass the entire organization, one or more departments within the organization, or one or more functions of a single department? Boundaries, are external to the system. 9-3b Database Design [p.450] The 2nd phase of the DBLC focuses on the design of the database model that will support company operations and objectives. There are 2 views of the data within the system: The business view of data as