This topic addresses categories of software processes, software life cycle models, software process adaptation, and practical considerations. A software development life cycle (SDLC) includes the software processes used to specify and transform software requirements into a deliverable software product. A software product life cycle (SPLC) includes a software development life cycle plus additional software processes that provide for deployment, maintenance, support, evolution, retirement, and all other inceptionto-retirement processes for a software product, including the software configuration management and software quality assurance processes that are applied throughout a software product life cycle. A software product life cycle may include multiple software development life cycles for evolving and enhancing the software.
nd enhancing the software. Individual software processes have no temporal ordering among them. The temporal relationships among software processes are provided by a software life cycle model: either an SDLC or SPLC. Life cycle models typically emphasize the key software processes within the model and their temporal and logical interdependencies and relationships. Detailed definitions of the software processes in a life cycle model may be provided directly or by reference to other documents.
In addition to conveying the temporal and logical relationships among software processes, the software development life cycle model (or models used within an organization) includes the control mechanisms for applying entry and exit criteria (e.g., project reviews, customer approvals, software testing, quality thresholds, demonstrations, team consensus). The output of one software process often provides the input for others (e.g., software requirements provide input for a software architectural design process and the software construction and software testing processes). Concurrent execution of several software process activities may produce a shared output (e.g., the interface specifications for interfaces among multiple software components developed by different teams). Some software processes may be regarded as less effective unless other software processes are being performed at the same time (e.g., software test planning during software requirements analysis can improve the software requirements).
Categories of Software Processes
Many distinct software processes have been defined for use in the various parts of the software development and software maintenance life cycles. These processes can be categorized as follows:
1. Primary processes include software processes for development, operation, and maintenance of software.
2. Supporting processes are applied intermittently or continuously throughout a software product life cycle to support primary processes; they include software processes such as configuration management, quality assurance, and verification and validation.
3. Organizational processes provide support for software engineering; they include training, process measurement analysis, infrastructure management, portfolio and reuse management, organizational process improvement, and management of software life cycle models.
4. Cross-project processes, such as reuse, software product line, and domain engineering; they involve more than a single software project in an organization.
Software processes in addition to those listed above include the following.
Project management processes include processes for
planning and estimating,
resource management,
measuring and controlling,
leading,
managing risk,
managing stakeholders, and
coordinating the primary, supporting, organizational, and
cross-project processes of software development and
maintenance projects.
Software processes are also developed for particular needs, such as process activities that address software quality characteristics (see the Software Quality KA). For example, security concerns during software development may necessitate one or more software processes to protect the security of the development environment and reduce the risk of malicious acts. Software processes may also be developed to provide adequate grounds for establishing confidence in the integrity of the software.
Software Life Cycle Models
The intangible and malleable nature of software permits a wide variety of software development life cycle models, ranging from linear models in which the phases of software development are accomplished sequentially with feedback and iteration as needed followed by integration, testing, and delivery of a single product; to iterative models in which software is developed in increments of increasing functionality on iterative cycles; to agile models that typically involve frequent demonstrations of working software to a customer or user representative who directs development of the software in short iterative cycles that produce small increments of working, deliverable software. Incremental, iterative, and agile models can deliver early subsets of working software into the user environment, if desired.
Linear SDLC models are sometimes referred to as predictive software development life cycle models, while iterative and agile SDLCs are referred to as adaptive software development life cycle models. It should be noted that various maintenance activities during an SPLC can be conducted using different SDLC models, as appropriate to the maintenance activities.
A distinguishing feature of the various software development life cycle models is the way in which software requirements are managed. Linear development models typically develop a complete set of software requirements, to the extent possible, during project initiation and planning. The software requirements are then rigorously controlled. Changes to the software requirements are based on change requests that are processed by a change control board (see Requesting, Evaluating and Approving Software Changes in the Change Control Board in the Software Configuration Management KA). An incremental model produces successive increments of working, deliverable software based on partitioning of the software requirements to be implemented in each of the increments. The software requirements may be rigorously controlled, as in a linear model, or there may be some flexibility in revising the software requirements as the software product evolves. Agile models may define product scope and high-level features initially; however, agile models are designed to facilitate evolution of the software requirements during the project.
It must be emphasized that the continuum of SDLCs from linear to agile is not a thin, straight line. Elements of different approaches may be incorporated into a specific model; for example, an incremental software development life cycle model may incorporate sequential software requirements and design phases but permit considerable flexibility in revising the software requirements and architecture during software construction.
Software Process Adaptation
Predefined SDLCs, SPLCs, and individual software processes often need to be adapted (or “tailored”) to better serve local needs. Organizational context, innovations in technology, project size, product criticality, regulatory requirements, industry practices, and corporate culture may determine needed adaptations. Adaptation of individual software processes and software life cycle models (development and product) may consist of adding more details to software processes, activities, tasks, and procedures to address critical concerns. It may consist of using an alternate set of activities that achieves the purpose and outcomes of the software process. Adaptation may also include omitting software processes or activities from a development or product life cycle model that are clearly inapplicable to the scope of work to be accomplished.
Practical Considerations
In practice, software processes and activities are often interleaved, overlapped, and applied concurrently. Software life cycle models that specify discrete software processes, with rigorously specified entry and exit criteria and prescribed boundaries and interfaces, should be recognized as idealizations that must be adapted to reflect the realities of software development and maintenance within the organizational context and business environment.
Another practical consideration: software processes (such as configuration management, construction, and testing) can be adapted to facilitate operation, support, maintenance, migration, and retirement of the software.
Additional factors to be considered when defining and tailoring a software life cycle model include required conformance to standards, directives, and policies; customer demands; criticality of the software product; and organizational maturity and competencies. Other factors include the nature of the work (e.g., modification of existing software versus new development) and the application domain (e.g., aerospace versus hotel management).
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Published on : 30-May-2018
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