The deeper the inheritance tree the more complex the design Many different

The deeper the inheritance tree the more complex the

This preview shows page 83 - 85 out of 103 pages.

(methods) from super-classes. The deeper the inheritance tree,the more complex the design. Many different object classes mayhave to be understood to understand the object classes at theleaves of the tree.Method fan-in/fan-outThis is directly related to fan-in and fan-out as described aboveand means essentially the same thing. However, it may beappropriate to make a distinction between calls from othermethods within the object and calls from external methods.Weighted methods perThis is the number of methods that are included in a classclassweighted by the complexity of each method. Therefore, a simplemethod may have a complexity of 1 and a large and complexmethod a much higher value. The larger the value for thismetric, the more complex the object class. Complex objects aremore likely to be more difficult to understand. They may not belogically cohesive so cannot be reused effectively as super-classes in an inheritance tree.Number of overridingThis is the number of operations in a super-class that are over-operationsridden in a sub-class. A high value for this metric indicates thatthe super-class used may not be an appropriate parent for thesub-class.Measurement analysisIt is not always obvious what data means Analysing collected data is very difficult. Professional statisticians should be consulted if available. Data analysis must take local circumstances into account. Measurement surprisesReducing the number of faults in a program leads to an increased number of help desk calls The program is now thought of as more reliable and so has a wider more diverse market. The percentage of users who call the help desk may have decreased but the total may increase; A more reliable system is used in a different way from a system where users work around the faults. This leads to more help desk calls. ZIPF’s LawZipf's Law as "the observation that frequency of occurrence of some event (P), as a function of the rank (i) when the rank is determined by the above frequency of occurrence, is a power-law function Pi~ 1/iawith the exponent aclose to unity (1)."
Page 84 Software EngineeringLet P(a random variable) represented the frequency of occurrence of a keyword in a program listing. It applies to computer programs written in any modern computer language. Without empirical proof because it's an obvious finding, that any computer program written in any programming language has a power law distribution, i.e., some keywords are used more than others. Frequency of occurrence of events is inversely proportional to the rank in this frequency of occurrence. When both are plotted on a log scale, the graph is a straight line. we create entities that don't exist except in computer memory at run time; we create logic nodes that will never be tested because it's impossible to test every logic branch; we create information flows in quantities that are humanly impossible to analyze with a glance;

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