CS161 SoftwareQualities

CS161 SoftwareQualities - Notes from Fundamentals of...

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Notes from Fundamentals of Software Engineering (Ghezzi et al. 1991) I. Types of Software Qualities External Qualities – In general, these are qualities that the user sees and cares about. Ex. reliability and user friendliness Internal Qualities – These are qualities that concern the developer. They help the developer achieve the external qualities. Ex. Verifiability helps achieve reliability. II. Qualities of the Software Process or Product Correctness Right result according to the spec . Spec. and software are equivalent. This means that the spec. must not be ambiguous! Specs. written in “natural language” (such as a program description written in English) are usually ambiguous. Code reuse (from standard libraries, rather than inventing new ones) helps improve correctness. Using high level languages helps too. For example, code written in assembly language is more likely to have errors than code written in Java. Reliability Dependable . The probability of failure is low. Users expect a newly released product to be “buggy.” But a new car or a new bridge is expected to be perfect. This is because of the immaturity of the software engineering field. Civil and mechanical engineering are more mature engineering disciplines. Robustness How well the product handles exceptional conditions such as hard disk crashes or wrong input from user . The attention devoted to making a program robust depends on the program’s purpose. If the program is to be used by novice computer users, it should be prepared to deal with incorrect inputs (letters where numbers are expected). If a program’s input always comes from a sensor, then incorrect input may not be an issue. If the program is to be used to control life- critical devices, then extra robustness is needed. Performance Efficiency in terms of space or time . Does it run slowly, use up too much memory, or use too much disk space. Is the algorithm scalable? This means, when the input size increases, can we still use this algorithm - or will it be too slow?
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