Software development approaches

Every software development methodology has more or less its own approach to software development. There is a set of more general approaches, which are developed into several specific methodologies. These approaches are:

• Waterfall: linear framework type.
• Prototyping: iterative framework type
• Incremental: combination of linear and iterative framework type
• Spiral: combination of linear and iterative framework type
• Rapid Application Development (RAD): Iterative Framework Type
• Extreme Programming.

Waterfall model
The waterfall model is a sequential development process, in which development is seen as flowing steadily downwards (like a waterfall) through the phases of requirements analysis, design, implementation, testing (validation), integration, and maintenance. The first formal description of the waterfall model is often cited to be an article published by Winston W. Royce[3] in 1970 although Royce did not use the term "waterfall" in this article.
Basic principles of the waterfall model are:

• Project is divided into sequential phases, with some overlap and splashback acceptable between phases.
• Emphasis is on planning, time schedules, target dates, budgets and implementation of an entire system at one time.
• Tight control is maintained over the life of the project through the use of extensive written documentation, as well as through formal reviews and approval/signoff by the user and information technology management occurring at the end of most phases before beginning the next phase.

Prototyping
Software prototyping, is the framework of activities during software development of creating prototypes, i.e., incomplete versions of the software program being developed.
Basic principles of prototyping are:

• Not a standalone, complete development methodology, but rather an approach to handling selected portions of a larger, more traditional development methodology (i.e. Incremental, Spiral, or Rapid Application Development (RAD)).
• Attempts to reduce inherent project risk by breaking a project into smaller segments and providing more ease-of-change during the development process.
• User is involved throughout the process, which increases the likelihood of user acceptance of the final implementation.
• Small-scale mock-ups of the system are developed following an iterative modification process until the prototype evolves to meet the users' requirements.
• While most prototypes are developed with the expectation that they will be discarded, it is possible in some cases to evolve from prototype to working system.
• A basic understanding of the fundamental business problem is necessary to avoid solving the wrong problem.
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Incremental
Various methods are acceptable for combining linear and iterative systems development methodologies, with the primary objective of each being to reduce inherent project risk by breaking a project into smaller segments and providing more ease-of-change during the development process.
Basic principles of incremental development are:

• A series of mini-Waterfalls are performed, where all phases of the Waterfall development model are completed for a small part of the systems, before proceeding to the next incremental, or
• Overall requirements are defined before proceeding to evolutionary, mini-Waterfall development of individual increments of the system, or
• The initial software concept, requirements analysis, and design of architecture and system core are defined using the Waterfall approach, followed by iterative Prototyping, which culminates in installation of the final prototype (i.e., working system). Spiral

spiral

The spiral model.

The spiral model is a software development process combining elements of both design and prototyping-in-stages, in an effort to combine advantages of top-down and bottom-up concepts. Basic principles:

• Focus is on risk assessment and on minimizing project risk by breaking a project into smaller segments and providing more ease-of-change during the development process, as well as providing the opportunity to evaluate risks and weigh consideration of project continuation throughout the life cycle.
• "Each cycle involves a progression through the same sequence of steps, for each portion of the product and for each of its levels of elaboration, from an overall concept-of-operation document down to the coding of each individual program."
• Each trip around the spiral traverses four basic quadrants: (1) determine objectives, alternatives, and constraints of the iteration; (2) Evaluate alternatives; Identify and resolve risks; (3) develop and verify deliverables from the iteration; and (4) plan the next iteration.
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• Begin each cycle with an identification of stakeholders and their win conditions, and end each cycle with review and commitment.

Rapid Application Development (RAD)
Rapid Application Development (RAD) is a software development methodology, which involves iterative development and the construction of prototypes. Rapid application development is a term originally used to describe a software development process introduced by James Martin in 1991.

Basic principles:

• Key objective is for fast development and delivery of a high quality system at a relatively low investment cost.
• Attempts to reduce inherent project risk by breaking a project into smaller segments and providing more ease-of-change during the development process.
• Aims to produce high quality systems quickly, primarily through the use of iterative Prototyping (at any stage of development), active user involvement, and computerized development tools. These tools may include Graphical User Interface (GUI) builders, Computer Aided Software Engineering (CASE) tools, Database Management Systems (DBMS), fourth-generation programming languages, code generators, and object-oriented techniques.
• Key emphasis is on fulfilling the business need, while technological or engineering excellence is of lesser importance.
• Project control involves prioritizing development and defining delivery deadlines or "timeboxes". If the project starts to slip, emphasis is on reducing requirements to fit the timebox, not in increasing the deadline.
• Generally includes Joint Application Development (JAD), where users are intensely involved in system design, either through consensus building in structured workshops, or through electronically facilitated interaction.
• Active user involvement is imperative.
• Iteratively produces production software, as opposed to a throwaway prototype.
• Produces documentation necessary to facilitate future development and maintenance.
• Standard systems analysis and design techniques can be fitted into this framework.

Other software development approaches
Other method concepts are:

• Object oriented development methodologies, such as Grady Booch's Object-oriented design (OOD), also known as object-oriented analysis and design (OOAD). The Booch model includes six diagrams: class, object, state transition, interaction, module, and process.
• Top-down programming: evolved in the 1970s by IBM researcher Harlan Mills (and Niklaus Wirth) in developed structured programming.
• Unified Process (UP) is an iterative software development methodology approach, based on UML. UP organizes the development of software into four phases, each consisting of one or more executable iterations of the software at that stage of development: Inception, Elaboration, Construction, and Guidelines. There are a number of tools and products available designed to facilitate UP implementation. One of the more popular versions of UP is the Rational Unified Process (RUP).
• Agile Software Development refers to a group of software development methodologies based on iterative development, where requirements and solutions evolve through collaboration between self-organizing cross-functional teams. The term was coined in the year 2001 when the Agile Manifesto was formulated.
• Integrated Methodology Software Development refers to a group of software development practices and deliverables that can be applied in a multitude (iterative, waterfall, spiral, agile) of software development environments, where requirements and solutions evolve through collaboration between self-organizing cross-functional teams.