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Software development
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Software development process
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Activities and steps
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Design
· Testing
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· Methodologies
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· Agile
· RAD
· RUP
· Spiral
· XP
· Lean
· Scrum
· V-Model
· TDD
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· Supporting disciplines
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· Tools
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· Compiler
· Debugger
· Profiler
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IDE
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A software development process, also known as a software development life cycle (SDLC), is a structure imposed on the development of asoftware product. Similar terms include software life cycle and software process. It is often considered a subset of systems development life cycle. There are several models for such processes, each describing
approaches to a variety of tasks or activities that take place during the process. Some
people consider a life-cycle model a more general term and a software
development process a more specific term. For example, there are many specific
software development processes that 'fit' the spiral life-cycle model. ISO/IEC 12207 is an international standard for software
life-cycle processes. It aims to be the standard that defines all the tasks
required for developing and maintaining software.
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Contents
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[edit]Overview
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The large and
growing body of software development organizations implement process
methodologies. Many of them are in the defense industry, which in
the U.S. requires a rating based on 'process models' to obtain
contracts.
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The international
standard for describing the method of selecting, implementing and monitoring
the life cycle for software is ISO/IEC 12207.
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A decades-long goal
has been to find repeatable, predictable processes that improve productivity
and quality. Some try to systematize or formalize the seemingly unruly task of
writing software. Others apply project management techniques to writing
software. Without project management, software projects can easily be delivered
late or over budget. With large numbers of software projects not meeting their
expectations in terms of functionality, cost, or delivery schedule, effective
project management appears to be lacking.
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Organizations may
create a Software Engineering Process Group (SEPG), which is the focal point for
process improvement. Composed of line practitioners who have varied skills, the
group is at the center of the collaborative effort of everyone in the
organization who is involved with software engineering process improvement.
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[edit]Software development
activities
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The activities of
the software development process represented in the waterfall model. There are
several other models to represent this process.
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[edit]Planning
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An important task in
creating a software program is extracting the requirements or requirements
analysis [1]. Customers typically have an abstract
idea of what they want as an end result, but not what software should do. Skilled and experienced software
engineers recognize incomplete, ambiguous, or even contradictory requirements
at this point. Frequently demonstrating live code may help reduce the risk that
the requirements are incorrect.
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Once the general
requirements are gathered from the client, an analysis of the scope of the
development should be determined and clearly stated. This is often called a
scope document.
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Certain
functionality may be out of scope of the project as a function of cost or as a
result of unclear requirements at the start of development. If the development
is done externally, this document can be considered a legal document so that if
there are ever disputes, any ambiguity of what was promised to the client can
be clarified.
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[edit]Implementation, testing and documenting
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Implementation is the part of the process where software engineers actually program the code for the project.
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Software testing is an integral and important phase of the
software development process. This part of the process ensures that defectsare recognized as
soon as possible.
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Documenting the internal design of software for the
purpose of future maintenance and enhancement is done throughout development.
This may also include the writing of an API, be
it external or internal. The software engineering process chosen by the
developing team will determine how much internal documentation (if any) is
necessary.Plan-driven models (e.g., Waterfall) generally
produce more documentation than Agile models.
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[edit]Deployment and maintenance
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Deployment starts after the code is appropriately
tested, approved for release, and sold or
otherwise distributed into a production environment. This may involve
installation, customization (e.g. by setting parameters to the customer's
values), testing, and possibly an extended period of evaluation.[citation
needed]
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Software training
and support is important, as software is only
effective if it is used correctly.[citation
needed]
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Maintaining and enhancing software to cope with newly
discovered faults or requirements can take substantial time
and effort, as missed requirements may force redesign of the software.[citation
needed]
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[edit]Software development models
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Several models exist
to streamline the development process. Each one has its pros and cons, and it's
up to the development team to adopt the most appropriate one for the project.
Sometimes a combination of the models may be more suitable.
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[edit]Waterfall model
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The waterfall model
shows a process, where developers are to follow these phases in order:
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In a strict
Waterfall model, after each phase is finished, it proceeds to the next one.
Reviews may occur before moving to the next phase which allows for the
possibility of changes (which may involve a formal change control process).
Reviews may also be employed to ensure that the phase is indeed complete; the
phase completion criteria are often referred to as a "gate" that the
project must pass through to move to the next phase. Waterfall discourages
revisiting and revising any prior phase once it's complete. This
"inflexibility" in a pure Waterfall model has been a source of criticism
by supporters of other more "flexible" models.
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[edit]Spiral model
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The key
characteristic of a Spiral model is risk management at regular stages in the
development cycle. In 1988, Barry Boehm published a formal software system
development "spiral model," which combines some key aspect of the waterfall model and rapid prototyping methodologies, but provided emphasis in a
key area many felt had been neglected by other methodologies: deliberate
iterative risk analysis, particularly suited to large-scale complex systems.
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The Spiral is
visualized as a process passing through some number of iterations, with the
four quadrant diagram representative of the following activities:
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formulate plans to:
identify software targets, selected to implement the program, clarify the
project development restrictions;
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Risk analysis: an
analytical assessment of selected programs, to consider how to identify and
eliminate risk;
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the implementation
of the project: the implementation of software development and verification;
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Risk-driven spiral
model, emphasizing the conditions of options and constraints in order to
support software reuse, software quality can help as a special goal of
integration into the product development. However, the spiral model has some
restrictive conditions, as follows:
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The spiral model
emphasizes risk analysis, and thus requires customers to accept this analysis
and act on it. This requires both trust in the developer as well as the
willingness to spend more to fix the issues, which is the reason why this model
is often used for large-scale internal software development.
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If the
implementation of risk analysis will greatly affect the profits of the project,
the spiral model should not be used.
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Software developers
have to actively look for possible risks, and analyze it accurately for the
spiral model to work.
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The first stage is
to formulate a plan to achieve the objectives with these constraints, and then
strive to find and remove all potential risks through careful analysis and, if
necessary, by constructing a prototype. If some risks can not be ruled out, the
customer has to decide whether to terminate the project or to ignore the risks
and continue anyway. Finally, the results are evaluated and the design of the
next phase begins.
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[edit]Iterative and incremental development
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Iterative development[2] prescribes the construction of initially
small but ever-larger portions of a software project to help all those involved
to uncover important issues early before problems or faulty assumptions can
lead to disaster.
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[edit]Agile development
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Agile software
development uses iterative development as a basis but advocates a lighter and
more people-centric viewpoint than traditional approaches. Agile processes use
feedback, rather than planning, as their primary control mechanism. The
feedback is driven by regular tests and releases of the evolving software.
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There are many
variations of agile processes:
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In Extreme Programming (XP), the phases are carried out in
extremely small (or "continuous") steps compared to the older,
"batch" processes. The (intentionally incomplete) first pass through
the steps might take a day or a week, rather than the months or years of each
complete step in the Waterfall model. First, one writes automated tests, to
provide concrete goals for development. Next is coding (by a pair of
programmers), which is complete when all the tests pass, and the programmers
can't think of any more tests that are needed. Design and architecture emerge
out of refactoring,
and come after coding. The same people who do the coding do design. (Only the
last feature — merging design and code — is common to all the other agile processes.) The
incomplete but functional system is deployed or demonstrated for (some subset
of) the users (at least one of which is on the development team). At this
point, the practitioners start again on writing tests for the next most
important part of the system.[3]
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Scrum
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[edit]Code and fix
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"Code and
fix" development is not so much a deliberate strategy as an artifact of
naiveté and schedule pressure on software developers.[4] Without much of a design in the way, programmersimmediately
begin producing code. At some point, testing begins (often late in the development
cycle), and the inevitable bugs must then be fixed before the product can
be shipped. See also:Continuous integration and Cowboy coding.
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[edit]Process improvement models
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Capability Maturity
Model Integration
o The Capability Maturity Model Integration (CMMI) is one of the leading models and
based on best practice. Independent assessments grade organizations on how well
they follow their defined processes, not on the quality of those processes or
the software produced. CMMI has replaced CMM.
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ISO 9000
o ISO 9000 describes standards for a formally
organized process to manufacture a product and the methods of managing and
monitoring progress. Although the standard was originally created for the
manufacturing sector, ISO 9000 standards have been applied to software development
as well. Like CMMI, certification with ISO 9000 does not guarantee the quality
of the end result, only that formalized business processes have been followed.
o
ISO/IEC 15504
o ISO/IEC 15504 Information
technology — Process assessment also known as Software Process
Improvement Capability Determination (SPICE), is a "framework for the
assessment of software processes". This standard is aimed at setting out a
clear model for process comparison. SPICE is used much like CMMI. It models
processes to manage, control, guide and monitor software development. This
model is then used to measure what a development organization or project team
actually does during software development. This information is analyzed to
identify weaknesses and drive improvement. It also identifies strengths that
can be continued or integrated into common practice for that organization or
team.
§ [edit]Formal
methods
§
Formal methods are mathematical approaches to solving
software (and hardware) problems at the requirements, specification and design
levels. Examples of formal methods include the B-Method, Petri nets, Automated theorem proving, RAISE and VDM. Various formal specification notations are
available, such as the Z notation. More generally, automata theory can be used to build up and validate
application behavior by designing a system of finite state
machines.
§
Finite state machine
(FSM) based methodologies allow executable software specification and
by-passing of conventional coding (see virtual finite state machine or event driven finite state machine).
§
Formal methods are
most likely to be applied in avionics software,
particularly where the software is safety critical. Software safety assurance
standards, such as DO178B demand formal methods at the highest
level of categorization (Level A).
§
Formalization of
software development is creeping in, in other places, with the application of Object Constraint Language (and specializations such as Java Modeling
Language) and especially with Model-driven architecture allowing execution of designs, if not
specifications.
§
Another emerging
trend in software development is to write a specification in some form of logic
(usually a variation of FOL), and then to directly execute the logic as though
it were a program. The OWL language, based on Description Logic, is
an example. There is also work on mapping some version of English (or another
natural language) automatically to and from logic, and executing the logic
directly. Examples are Attempto Controlled English, and Internet Business
Logic, which do not seek to control the vocabulary or syntax. A feature of
systems that support bidirectional English-logic mapping and direct execution
of the logic is that they can be made to explain their results, in English, at
the business or scientific level.
§
The Government
Accountability Office, in a 2003 report on one of the Federal Aviation Administration’s
air traffic control modernization programs,[5] recommends following the agency’s
guidance for managing major acquisition systems by
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establishing,
maintaining, and controlling an accurate, valid, and current performance
measurement baseline, which would include negotiating all authorized, unpriced
work within 3 months;
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conducting an
integrated baseline review of any major contract modifications within 6 months;
and
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preparing a rigorous
life-cycle cost estimate, including a risk assessment, in accordance with the
Acquisition System Toolset’s guidance and identifying the level of uncertainty
inherent in the estimate.
§ [edit]See
also
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[edit]Development methods
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[edit]Related subjects
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Project
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