【文章內(nèi)容簡介】 nt, configuring operating systems parameters and user access privileges, and running diagnostic test cases to assure the viability of basic system operation. ? Training and Use: providing system users with instructional aids and guidance for understanding the system39。s capabilities and limits in order to effectively use the system. ? Software Maintenance: sustaining the useful operation of a system in its host/target environment by providing requested functional enhancements, repairs, performance improvements, and conversions. What is a software life cycle model? A software life cycle model is either a descriptive or prescriptive characterization of 8 how software is or should be developed. A descriptive model describes the history of how a particular software system was developed. Descriptive models may be used as the basis for understanding and improving software development processes, or for building empirically grounded prescriptive models (Curtis, Krasner, Iscoe, 1988). A prescriptive model prescribes how a new software system should be developed. Prescriptive models are used as guidelines or frameworks to anize and structure how software development activities should be performed, and in what order. Typically, it is easier and more mon to articulate a prescriptive life cycle model for how software systems should be developed. This is possible since most such models are intuitive or well reasoned. This means that many idiosyncratic details that describe how a software systems is built in practice can be ignored, generalized, or deferred for later consideration. This, of course, should raise concern for the relative validity and robustness of such life cycle models when developing different kinds of application systems, in different kinds of development settings, using different programming languages, with differentially skilled staff, etc. However, prescriptive models are also used to package the development tasks and techniques for using a given set of software engineering tools or environment during a development project. Descriptive life cycle models, on the other hand, characterize how particular software systems are actually developed in specific settings. As such, they are less mon and more difficult to articulate for an obvious reason: one must observe or collect data throughout the life cycle of a software system, a period of elapsed time often measured in years. Also, descriptive models are specific to the systems observed and only generalizable through systematic parative analysis. Therefore, this suggests the prescriptive software life cycle models will dominate attention until a sufficient base of observational data is available to articulate empirically grounded descriptive life cycle models. These two characterizations suggest that there are a variety of purposes for articulating software life cycle models. These characterizations serve as a ? Guideline to anize, plan, staff, budget, schedule and manage software project work over anizational time, space, and puting environments. ? Prescriptive outline for what documents to produce for delivery to client. ? Basis for determining what software engineering tools and methodologies will be most appropriate to support different life cycle activities. 9 ? Framework for analyzing or estimating patterns of resource allocation and consumption during the software life cycle (Boehm 1981). ? Basis for conducting empirical studies to determine what affects software productivity, cost, and overall quality. What is a software process model? In contrast to software life cycle models, software process models often represent a worked sequence of activities, objects, transformations, and events that embody strategies for software evolution. Such models can be used to develop more precise and formalized descriptions of software life cycle activities. Their power emerges from their utilization of a sufficiently rich notation, syntax, or semantics, often suitable for putational processing. Software process works can be viewed as representing multiple interconnected task chains (Kling 1982, Garg 1989). Task chains represent a nonlinear sequence of actions that structure and transform available putational objects (resources) into intermediate or finished products. Nonlinearity implies that the sequence of actions may be nondeterministic, iterative, acmodate ultiple/parallel alternatives, as well as partially ordered to account for incremental progress. Task actions in turn can be viewed a nonlinear sequences of primitive actions which denote atomic units of puting work, such as a user39。s selection of a ommand or menu entry using a mouse or keyboard. Winograd and others have referred to these units of cooperative work between people and puters as structured discourses of work (Winograd 1986), while task chains have bee popularized under the name of workflow (Bolcer 1998). Task chains can be employed to characterize either prescriptive or descriptive ac