COMP6005 (v.1) Object Oriented Software Engineering or any previous version Prerequisite(s): COMP1002 (v.1) Data.
Lines of code and functional point metrics can be used for estimating object-oriented software projects. However, these metrics are not appropriate in the case of incremental software development as they do not provide adequate details for effort and schedule estimation. Thus, for object-oriented projects, different sets of metrics have been proposed. These are listed below.
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- Number of scenario scripts: Scenario scripts are a sequence of steps, which depict the interaction between the user and the application. A number of scenarios is directly related to application size and number of test cases that are developed to test the software, once it is developed. Note that scenario scripts are analogous to use-cases.
- Number of key classes: Key classes are independent components, which are defined in object -oriented analysis. As key classes form the core of the problem domain, they indicate the effort required to develop software and the amount of ‘reuse’ feature to be applied during the development process.
- Number of support classes: Classes, which are required to implement the system but are indirectly related to the problem domain, are known as support classes. For example, user interface classes and computation class are support classes. It is possible to develop a support class for each key class. Like key classes, support classes indicate the effort required to develop software and the amount of ‘reuse’ feature to be applied during the development process.
- Average number of support classes per key class: Key classes are defined early in the software project while support classes are defined throughout the project. The estimation process is simplified if the average number of support classes per key class is already known.
- Number of subsystems: A collection of classes that supports a function visible to the user is known as a subsystem. Identifying subsystems makes it easier to prepare a reasonable schedule in which work on subsystems is divided among project members.
The afore-mentioned metrics are collected along with other project metrics like effort used, errors and defects detected, and so on. After an organization completes a number of projects, a database is developed, which shows the relationship between object-oriented measure and project measure. This relationship provides metrics that help in project estimation.
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Object Oriented Software Engineering Pdf
1.7 Object-Oriented Programming and Software Engineering
Object-oriented programming is an evolutionary development in softwareengineering. The foundation for many object-oriented languages wereestablished by decades of software engineering experience thatmotivated the invention of language features such as closedprocedures, modules and abstract data types. Also important were thewidely recognized value of such software engineering techniques asinformation hiding, encapsulation, strict enforcement of interfaces,and layering.
Object-oriented programming address (at least) the three majorsoftware engineering goals shown in this figure:
The language features that address these issues are those of objects,classes, inheritance, polymorphism, templates, and design patterns.
Reusability is an important issue in software engineering for at leasttwo major reasons. First reusability is one means to cope with thepressures of producing ever larger and more functional systems in anever decreasing development cycle (time to market). Reusability allowsdevelopers to be more efficient because the same code can be developedonce and used in many different applications. Second, reliability canbe improved by reusing previously developed, and previously tested,components. The development of new code entails the additional costsin time and money of testing, validation, and verification of the newcode. Much of these expenses can be avoided by using 'off-the-shelf'components.
Software reuse is certainly not a goal unique to object-orientedprogramming. While libraries of procedures proved this approach to beuseful, in practice procedures were too primitive a unit to promoteextensive reuse. Objects and classes are more sophisticated mechanismsfor achieving software reuse because they bind together morecompletely all the aspects of an entire abstraction. Therefore, theabstraction can more easily be transported across applications. Any ofthe forms of generalization also contribute to reuse. A class in aninheritance hierarchy can be reused directly when it serves as ageneralized base class from which a new class is derived byspecialization. Templates can be reused by supplying differentparameters for the template arguments. Design patterns allow designexperience and success to be reused across designers.
Extensibility in software is important because software systems arelong-lived and are subject to user's demands for new features andadded capability. Object-oriented programming can help to satisfythis need through inheritance. Recall that inheritance is ageneralization/specialization hierarchy. Referring to the Windowhierarchy discussed earlier, extensibility is possible in twoways. The first way in which a generalization/specialization hierarchysupports extensibility is that any new attributes or behavior that isadded to a more generalized concept (e.g., Window) will automaticallybecome part of the attributes and behavior of its specializations(e.g., Frame, Item, Button). For example, as shown below, if theWindow abstraction is enhanced to include a color with which theWindow would be displayed on the screen, then the attribute'currentColor' and the behavior 'setColor' might be added toWindow. It would then be possible to manipulate the color of a Windowbut all its specializations as well.
Object-oriented Software Engineering By Jacobson
The second way in which a generalization/specialization hierarchysupports extensibility is that the hierarchy itself can beextended. New additions can be made under any existing node. Forexample, as shown below, the TextWindow might be specialized to aHyperTextWindow by including additional attributes and additionalbehavior that distinguishes ordinary words from those words that arehyperlink and can be clicked-on to transfer to another place in thetext.
Flexibility in software systems means, in part, that additions, variations ormodification can be made without the need to modify numerous placesin the system's code. Historically, many software systems were verybrittle in that the addition of a small change could only beaccomodated by making modifications in many, and often aparrentlyunrelated, parts of the existing system. This brittle property stoodin marked contrast to the prevaling notion that, nlike hardwaresystems, software system were supposed to be extremelymaleable and changes can be made easily.
Object Oriented Software Engineering Notes
Object-oriented programming contributes to flexibility in twoways. First, the separation of an interface from its implementationallows the user of the interface to remain unaffected by changes inthe implementation. Thus, a modification can be made to theimplementation (e.g., to improve its efficiency or reliability)without requiring any changes in the code that uses theinterface. Second, polymorphism allows variations and additions to bemade to the set of classes over which the polymorphism applies. Forexample, referring to the Window hierarchy, consider adding a new kindof interaction Item, a RadioButton. Since Items can be placed in aPanel, it would seem necessary to modify the Panel to allow a Panel tomanipulate the newly created RadioButton. However, the Panel can usepolymorphism so that the Panel's algorithms only rely on the moregeneral attributes and behavior of an object (i.e., that it is a kindof Item) and does not need to be aware of the exact 'type' (i.e.,RadiButton) of the object. Using this approach, the Panel can bedesigned to operate on Items. Any newly created Item, even one - likethe RadioButton - that is created after the Panel is already written,automatically can be manipulated by a Panel without changing the codeof the Panel.
Object Oriented Programming Tutorial Pdf
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