Objectives: Introduction Over View of System Analysis and Design
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- 8.2.1.1 Approaches to Reliability
| 8.2 Design Objectives The two operational design objectives continually sought by developers are systems reliability and maintainability. 8.2.1 Reliable Systems A system is said to have reliability if it does not produce dangerous or costly failures when it is used in a reasonable manner, that is, in a manner that atypical user expects is normal. This definition recognizes that systems may not always be used in the ways that designers expect. There are changes in the ways users use a system and also in business operations. However, there are steps analysts can take to ensure that the system is reliable when it is installed and that the reliability can be maintained after implementation. 8.2.1.1 Approaches to Reliability There are two levels of reliability. The first is that the system is meeting the right requirements. For instance, a system might be expected to have specific security features or controls built into it by the users. But if the design fails to specify them and permits the loss of funds or merchandise fora lengthy time before someone detects the problem, the system is not reliable. Reliability at the design level is possible only if the analyst performed a thorough and effective determination of systems requirements. A careful and thorough systems study is needed to satisfy this aspect of reliability. The second level of systems reliability involves the actual workings of the system delivered to the user. At this level, systems reliability is interwoven with software engineering and development. An error occurs whenever the system does not produce the expected output. While it is true that no program is ever fully debugged or fully tested, nor proven correct – a fact that startles many users and aspiring programmers – errors are not limited to the correct use of programming syntax alone. The computing industry, largely through the work of Glenford Myers, has come to distinguish between error and failures. A failure is the occurrence of a software error, weighted by its seriousness. For example, if an inventory program is developed to truncate rather than round half – rupees when calculating the value of materials on handed, it is an error if specifications call for rounding. But it maybe of no consequence to the user, who in fact does not consider this a failure. However, if the program regularly skips certain items or indicates they are out of stock when in fact the records show they are in stock, there is a serious failure. Download 0.94 Mb. Share with your friends:
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