software development cycle

In software engineering, a software development process is a process of dividing software development work into smaller, parallel, or sequential steps or sub-processes to improve design, product management. It is also known as a software development life cycle (SDLC). The methodology may include the pre-definition of specific deliverables and artifacts that are created and completed by a project team to develop or maintain an application.

Most modern development processes can be vaguely described as agile. Other methodologies include waterfall, prototyping, iterative and incremental development, spiral development, rapid application development, and extreme programming.

A life-cycle "model" is sometimes considered a more general term for a category of methodologies and a software development "process" a more specific term to refer to a specific process chosen by a specific organization. For example, there are many specific software development processes that fit the spiral life-cycle model. The field is often considered a subset of the systems development life cycle.

History

The software development methodology (also known as SDM) framework didn't emerge until the 1960s. According to Elliott (2004), the systems development life cycle (SDLC) can be considered to be the oldest formalized methodology framework for building information systems. The main idea of the SDLC has been "to pursue the development of information systems in a very deliberate, structured and methodical way, requiring each stage of the life cycle––from the inception of the idea to delivery of the final system––to be carried out rigidly and sequentially"Geoffrey Elliott (2004) ''Global Business Information Technology: an integrated systems approach''. Pearson Education. p.87. within the context of the framework being applied. The main target of this methodology framework in the 1960s was "to develop large scale functional business systems in an age of large scale business conglomerates. Information systems activities revolved around heavy data processing and number crunching routines".

Methodologies, processes, and frameworks range from specific prescriptive steps that can be used directly by an organization in day-to-day work, to flexible frameworks that an organization uses to generate a custom set of steps tailored to the needs of a specific project or group. In some cases, a "sponsor" or "maintenance" organization distributes an official set of documents that describe the process. Specific examples include:

; 1970s
* Structured programming since 1969
* Cap Gemini SDM, originally from PANDATA, the first English translation was published in 1974. SDM stands for System Development Methodology
; 1980s
* Structured systems analysis and design method (SSADM) from 1980 onwards
* Information Requirement Analysis/Soft systems methodology
; 1990s
* Object-oriented programming (OOP) developed in the early 1960s and became a dominant programming approach during the mid-1990s
* Rapid application development (RAD), since 1991
* Dynamic systems development method (DSDM), since 1994
* Scrum, since 1995
* Team software process, since 1998
* Rational Unified Process (RUP), maintained by IBM since 1998
* Extreme programming, since 1999
; 2000s
* Agile Unified Process (AUP) maintained since 2005 by Scott Ambler
* Disciplined agile delivery (DAD) Supersedes AUP

2010s

* Scaled Agile Framework (SAFe)
* Large-Scale Scrum (LeSS)
* DevOps

It is notable that since DSDM in 1994, all of the methodologies on the above list except RUP have been agile methodologies - yet many organizations, especially governments, still use pre-agile processes (often waterfall or similar). Software process and software quality are closely interrelated; some unexpected facets and effects have been observed in practice

Among these, another software development process has been established in open source. The adoption of these best practices known and established processes within the confines of a company is called inner source.

Prototyping

Software prototyping is about creating prototypes, i.e. incomplete versions of the software program being developed.

The basic principles are:

* Prototyping is not a standalone, complete development methodology, but rather an approach to try out particular features in the context of a full methodology (such as 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.
* The client is involved throughout the development process, which increases the likelihood of client acceptance of the final implementation.
* While some 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 problems, but this is true for all software methodologies.

Methodologies

Agile development

"Agile software development" refers to a group of software development frameworks based on iterative development, where requirements and solutions evolve via collaboration between self-organizing cross-functional teams. The term was coined in the year 2001 when the Agile Manifesto was formulated.

Agile software development uses iterative development as a basis but advocates a lighter and more people-centric viewpoint than traditional approaches. Agile processes fundamentally incorporate iteration and the continuous feedback that it provides to successively refine and deliver a software system.

The Agile model also includes the following software development processes:

* Dynamic systems development method (DSDM)
* Kanban
* Scrum
* Crystal
* Atern
* Lean software development

Continuous integration

Continuous integration is the practice of merging all developer working copies to a shared mainline several times a day. Grady Booch first named and proposed CI in his 1991 method, although he did not advocate integrating several times a day. Extreme programming (XP) adopted the concept of CI and did advocate integrating more than once per day – perhaps as many as tens of times per day.

Incremental development

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.

There are three main variants of incremental development:

# A series of mini-Waterfalls are performed, where all phases of the Waterfall are completed for a small part of a system, before proceeding to the next increment, or
# Overall requirements are defined before proceeding to evolutionary, mini-Waterfall development of individual increments of a system, or
# The initial software concept, requirements analysis, and design of architecture and system core are defined via Waterfall, followed by incremental implementation, which culminates in installing the final version, a working system.

Rapid application development

Rapid application development (RAD) is a software development methodology, which favors iterative development and the rapid construction of prototypes instead of large amounts of up-front planning. The "planning" of software developed using RAD is interleaved with writing the software itself. The lack of extensive pre-planning generally allows software to be written much faster, and makes it easier to change requirements.

The rapid development process starts with the development of preliminary data models and business process models using structured techniques. In the next stage, requirements are verified using prototyping, eventually to refine the data and process models. These stages are repeated iteratively; further development results in "a combined business requirements and technical design statement to be used for constructing new systems".

The term was first used to describe a software development process introduced by James Martin in 1991. According to Whitten (2003), it is a merger of various structured techniques, especially data-driven information technology engineering, with prototyping techniques to accelerate software systems development.Whitten, Jeffrey L.; Lonnie D. Bentley, Kevin C. Dittman. (2003). ''Systems Analysis and Design Methods''. 6th edition. .

The basic principles of rapid application development are:

* 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 via 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 design (JAD), where users are intensely involved in system design, via consensus building in either structured workshops, or 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 methods can be fitted into this framework.

Waterfall development

The waterfall model is a sequential development approach, in which development is seen as flowing steadily downwards (like a waterfall) through several phases, typically:

* Requirements analysis resulting in a software requirements specification
* Software design
* Implementation
* Testing
* Integration, if there are multiple subsystems
* Deployment (or Installation)
* Maintenance

The first formal description of the method is often cited as an article published by Winston W. Royce in 1970, although Royce did not use the term "waterfall" in this article. Royce presented this model as an example of a flawed, non-working model.

The basic principles are:

* The Project is divided into sequential phases, with some overlap and splash back 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 via extensive written documentation, formal reviews, and approval/signoff by the user and information technology management occurring at the end of most phases before beginning the next phase. Written documentation is an explicit deliverable of each phase.

The waterfall model is a traditional engineering approach applied to software engineering. A strict waterfall approach discourages revisiting and revising any prior phase once it is complete. This "inflexibility" in a pure waterfall model has been a source of criticism by supporters of other more "flexible" models. It has been widely blamed for several large-scale government projects running over budget, over time and sometimes failing to deliver on requirements due to the Big Design Up Front approach. Except when contractually required, the waterfall model has been largely superseded by more flexible and versatile methodologies developed specifically for software development. See Criticism of Waterfall model.

Spiral development

In 1988, Barry Boehm