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毕业设计（论文）
PHYSICAL SCHEMA
The physical schema is a description of the physical structure of the database. If, for example, conventional indexed-sequential files are used to store the database, then this will be stated in the physical schema. It will also contain details of record formats, blocking factors etc. The physical schema is constructed as an essential part of the design process. However, it may also be used as an integeral part of he operational database system as discussed below. The physical schema is sometimes called the internal schema.
PHYSICAL STORAGE STRUCTURE
The structure in which the database actually resides is termed the physical storage structure. It typically consists of disc files, tapes, mainstore, indices and programs to manipulate these components. BACK-UP AND RECOVERY SYSTEM
The back-up and recovery system is the module which rebuilds the database after corruption due to hardware or software failure. Understanding the Application Tasks
One of the often-neglected steps on building software is really understanding the end user’s job-the that computer automation is intended to support.
Occasionally, this is because the application itself is quite specialized; more often, it is because the approach to design tends to be data-oriented. Frequently, these are the major question asked in the analysis: ■ What data should be captured? ■ How should the data be processed? ■ How should the data be reported?
These question expand into a series of sub question ,and include issues such as input forms, Codes, screen layouts, computations, postings, corrections, audit trails, retention, storage volumes, processing cycles, report formatting, distribution, and maintenance. there are all vitally important areas. One difficulty, however, is that they all focus solely on data.
People use data, but they do tasks. One might argue that while this may be true of professional workers. Key-entry clerks really only transfer data from an input form to a keyboard; their tasks are very data-oriented. This is a fair
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毕业设计（论文）
portrayal of their jobs today, but is this a consequence of the real job that need to get done, or is it a symptom of the computer application? Using humans as input devices, particularly for data that is voluminous, consistent in format (as on forms), and in a limited range of variability, is an expensive and antiquated, not to mention dehumanizing, method of capturing data.
This may sound like so much philosophy, but it has practical import in the way application design is done. People use data, but they do tasks. And they don’t do tasks through o completion one at a time. They do several tasks that are subset of or in intersection with each other, and they so them all at once, in parallel.
When designers allow this idea to direct the analysis and creation of an Application, rather than focusing on the data orientation that has been historically dominant, the very nature of the effort changes significantly. Why have windowing environments been so successful? Because they allow a user to shut down and exit one in order to begin another. The windowing environment comes closer to mapping the way people really think and work than the old “one thing at a time “approach ever did. This lesson should not be lost. It should be built upon.
Understanding the application tasks means going far beyond identifying the data elements, normalizing them, and creating screens, processing programs, and reports. It means really understanding what the users do and what their tasks are, and designing the application to be responsive to those tasks, not just to capture the data, associated with them. In fact, when the orientation is toward the data, the resulting design will inevitably distort the user’s tasks rather than support them.
How do you design an application that is responsive to tasks rather than data? The biggest hurdle is simply understanding that focusing on tasks is necessary. This allows you to approach the analysis of the business from a fresh perspective.
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