NationMaster - Encyclopedia: Extreme programming

Extreme Programming (or XP) is a software engineering methodology, the most prominent^{[citation needed]} of several agile software development methodologies, prescribing a set of daily stakeholder practices that embody and encourage particular XP values (below). Proponents believe that exercising these practices—traditional software engineering practices taken to so-called "extreme" levels—leads to a development process that is more responsive to customer needs ("agile") than traditional methods, while creating software of better quality.^[1] This does not cite any references or sources. ... In sytems and software engineering, requirements analysis encompasses those tasks that go into determining the requirements of a new or altered system, taking account of the possibly conflicting requirements of the various stakeholders, such as users. ... The software architecture of a program or computing system is the structure or structures of the system, which comprise software elements, the externally visible properties of those elements, and the relationships between them. ... Computer programming (often shortened to programming or coding) is the process of writing, testing, and maintaining the source code of computer programs. ... Software testing is the process used to measure the quality of developed computer software. ... Software deployment is all of the activities that make a software system available for use. ... Agile software development is a conceptual framework for undertaking software engineering projects that embraces and promotes evolutionary change throughout the entire life-cycle of the project. ... The Cleanroom Software Engineering process is a software development process intended to produce software with a certifiable level of reliability. ... Iterative and Incremental development is a software development process developed in response to the weaknesses of the more traditional waterfall model. ... Rapid application development (RAD), is a software development process developed initially by James Martin in the 1980s. ... The Rational Unified Process (RUP) is an iterative software development process framework created by the Rational Software Corporation, since 2002 a division of IBM. The RUP is not a single concrete prescriptive process, but rather an adaptable process framework, intended to be tailored by the development organizations and software project... 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. ... The waterfall model is a sequential software development model (a process for the creation of software) 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. ... Software Configuration Management (SCM) is part of configuration management (CM). ... Software Documentation or Source Code Documentation is written text that accompanies computer software. ... Software testing is the process used to help identify the correctness, completeness, security and quality of developed computer software. ... Project Management is the discipline of organizing and managing resources (e. ... User experience design is a subset of the field of experience design which pertains to the creation of the architecture and interaction models which impact a users perception of a device or system. ... This does not cite any references or sources. ... Agile software development is a conceptual framework for undertaking software engineering projects that embraces and promotes evolutionary change throughout the entire life-cycle of the project. ... Extreme Programming (or XP) is a software engineering methodology, the most prominent of several agile software development methodologies. ... Extreme Programming (or XP) is a software engineering methodology, the most prominent of several agile software development methodologies. ...

Proponents of XP and agile methodologies in general regard ongoing changes to requirements as a natural, inescapable and desirable aspect of software development projects; they believe that adaptability to changing requirements at any point during the project life is a more realistic and better approach than attempting to define all requirements at the beginning of a project and then expending effort to control changes to the requirements. This article is about engineering. ...

History

Extreme Programming was created by Kent Beck during his work on the Chrysler Comprehensive Compensation System (C3) payroll project. Kent Beck became the C3 project leader in March 1996 and began to refine the development methodology used on the project. Kent Beck wrote a book on the methodology, and in October 1999, Extreme Programming Explained was published. Chrysler canceled the C3 project in February 2000, and although some see that initial failure as a problem with XP, the methodology had caught on in the software engineering field. As of 2007, a number of software-development projects continue to use Extreme Programming as their methodology. Kent Beck is the creator of Extreme Programming and is one of the founders of the Agile Manifesto. ... The Chrysler Comprehensive Compensation System was a plan in the Chrysler American Automobile Corporation to redo their payroll computer system. ... The technical expert role that drives the detailed implementation of a specific aspect of the project, and is directly responsible for all project deliverables. ... Software engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software. ...

Although Extreme Programming itself is quite new, many of its practices have been around for some time; the methodology, after all, takes "best practices" to extreme levels. For example, the "practice of test-first development, planning and writing tests before each micro-increment" was used as early as NASA's Project Mercury, in the early 1960s (Larman 2003). Refactoring, modularity, bottom-up and incremental design were described by Leo Brodie in his book published in 1984^[2].

Origins

Software development in the 1990s was shaped by two major influences: internally, object-oriented programming replaced procedural programming as the programming paradigm favored by some in the industry; externally, the rise of the Internet and the dot-com boom emphasized speed-to-market and company-growth as competitive business factors. Rapidly-changing requirements demanded shorter product life-cycles, and were often incompatible with traditional methods of software development. Object-oriented programming (OOP) is a programming paradigm that uses objects to design applications and computer programs. ... This does not adequately cite its references or sources. ... Dot-com (also dotcom or redundantly dot. ... â€” This article is about managing the life of a product in the market. ...

The Chrysler Comprehensive Compensation project was started in order to determine the best way to use object technologies, using the payroll systems at Chrysler as the object of research, with Smalltalk as the language and GemStone as the data access layer. They brought in Kent Beck, a prominent Smalltalk practitioner, to do performance tuning on the system, but his role expanded as he noted several issues they were having with their development process. He took this opportunity to propose and implement some changes in their practices based on his work with his frequent collaborator, Ward Cunningham. For other uses, see Small talk. ... Object Oriented Database One of List_of_object-oriented_database_management_systems External links [1] Category: ... A Data access layer is a layer of a computer program which provides simplified access to data stored in persistent storage of some kind, such as an entity-relational database. ... Kent Beck is the creator of Extreme Programming and is one of the founders of the Agile Manifesto. ... Performance tuning is the improvement of system performance. ... Oh Yes, Hes Ward Cunningham! Howard Cunningham redirects here. ...

Beck invited Ron Jeffries to the project to help develop and refine these methods. Jeffries thereafter acted as a coach to instill the practices as habits in the C3 team. Ron Jeffries is one of the founders of the extreme programming (or XP) software development methodology. ...

Information about the principles and practices behind XP was disseminated to the wider world through discussions on the original Wiki, Cunningham's WikiWikiWeb. Various contributors discussed and expanded upon the ideas, and some spin-off methodologies resulted (see agile software development). Also, XP concepts have been explained, for several years, using a hyper-text system map on the XP website at "www.extremeprogramming.org" circa 1999 (website ^XPORG). Look up Wiki in Wiktionary, the free dictionary. ... WikiWikiWeb The WikiWikiWeb, or simply WikiWiki or Wiki (with a capital W), is the first ever wiki, written in Perl. ... Agile software development is a conceptual framework for undertaking software engineering projects that embraces and promotes evolutionary change throughout the entire life-cycle of the project. ...

Beck edited a series of books on XP, beginning with his own Extreme Programming Explained (1999, ISBN 0-201-61641-6), spreading his ideas to a much larger, yet very receptive, audience. Authors in the series went through various aspects attending XP and its practices, even a book critical of the practices.

Current state

XP created quite a buzz in the late 1990s and early 2000s, seeing adoption in a number of environments radically different from its origins.

The high discipline required by the original practices often went by the wayside, causing certain practices to be deprecated or left undone on individual sites. Agile development practices have not stood still, and XP is still evolving, assimilating more lessons from experiences in the field. In the second edition of Extreme Programming Explained, Beck added more values and practices and differentiated between primary and corollary practices.

Goal of XP

The main aim of XP is to reduce the cost of change. In traditional system development methods (like SSADM) the requirements for the system are determined at the beginning of the development project and often fixed from that point on. This means that the cost of changing the requirements at a later stage (a common feature of software engineering projects) will be high. Structured Systems Analysis and Design Methodology (SSADM) is a systems approach to the analysis and design of information systems. ...

XP sets out to reduce the cost of change by introducing basic values, principles and practices. By applying XP, a system development project should be more flexible with respect to changes.

XP values

Extreme Programming initially recognized four values in 1999. A new value was added in the second edition of Extreme Programming Explained. The five values are:

Building software systems requires communicating system requirements to the developers of the system. In formal software development methodologies, this task is accomplished through documentation. Extreme Programming techniques can be viewed as methods for rapidly building and disseminating institutional knowledge among members of a development team. The goal is to give all developers a shared view of the system which matches the view held by the users of the system. To this end, Extreme Programming favors simple designs, common metaphors, collaboration of users and programmers, frequent verbal communication, and feedback. Communication is a process that allows beings - in particular humans - to exchange information by several methods. ... Wikiquote has a collection of quotations related to: Simplicity Simplicity is the property, condition, or quality of being simple or un-combined. ... It has been suggested that this article or section be merged with Feedback loop. ... Bravery and Fortitude redirect here. ... This article does not cite any references or sources. ...

Extreme Programming encourages starting with the simplest solution and refactoring to better ones. The difference between this approach and more conventional system development methods is the focus on designing and coding for the needs of today instead of those of tomorrow, next week, or next month. Proponents of XP acknowledge the disadvantage that this can sometimes entail more effort tomorrow to change the system; their claim is that this is more than compensated for by the advantage of not investing in possible future requirements that might change before they become relevant. Coding and designing for uncertain future requirements implies the risk of spending resources on something that might not be needed. Related to the "communication" value, simplicity in design and coding should improve the (quality of) communication. A simple design with very simple code could be easily understood by most programmers in the team. Refactoring is the process of rewriting a computer program or other material to improve its structure or readability, while explicitly keeping its meaning or behavior. ...

Within Extreme Programming, feedback relates to different dimensions of the system development:

Feedback is closely related to communication and simplicity. Flaws in the system are easily communicated by writing a unit test that proves a certain piece of code will break. The direct feedback from the system tells programmers to recode this part. A customer is able to test the system periodically according to the functional requirements (aka user stories). To quote Kent Beck, "Optimism is an occupational hazard of programming, feedback is the treatment."^{[citation needed]} In computer programming, a unit test is a procedure used to validate that a particular module of source code is working properly. ... [noun phrase] An acceptance test in engineering is a test that a user/sponsor and manufacturer/producer jointly perform on a finished, engineered product/system through black-box testing (i. ... A user story is a software system requirement formulated as one or two sentences in the everyday language of the user. ... Kent Beck is the creator of Extreme Programming and is one of the founders of the Agile Manifesto. ...

Several practices embody courage. One is the commandment to always design and code for today and not for tomorrow. This is an effort to avoid getting bogged down in design and requiring a lot of effort to implement anything else. Courage enables developers to feel comfortable with refactoring their code when necessary. This means reviewing the existing system and modifying it so that future changes can be implemented more easily. Another example of courage is knowing when to throw code away: courage to remove source code that is obsolete, no matter how much effort was used to create that source code. Also, courage means persistence: A programmer might be stuck on a complex problem for an entire day, then solve the problem quickly the next day, if only they are persistent. Refactoring is the process of rewriting a computer program or other material to improve its structure or readability, while explicitly keeping its meaning or behavior. ...

The respect value manifests in several ways. In Extreme Programming, team members respect each other because programmers should never commit changes that break compilation, that make existing unit-tests fail, or that otherwise delay the work of their peers. Members respect their work by always striving for high quality and seeking for the best design for the solution at hand through refactoring.

Adopting four earlier values led to respect gained from others in team. Nobody on the team should feel unappreciated or ignored. This ensures high level of motivation and encourages loyalty toward the team, and the goal of the project. This value is very dependent upon the other values, and is very much oriented toward people in a team.

Principles

The principles that form the basis of XP are based on the values just described and are intended to foster decisions in a system development project. The principles are intended to be more concrete than the values and more easily translated to guidance in a practical situation.

Feedback is most useful if it is done rapidly. The time between an action and its feedback is critical to learning and making changes. In Extreme Programming, unlike traditional system development methods, contact with the customer occurs in small iterations. The customer has clear insight into the system that is being developed. He or she can give feedback and steer the development as needed.

Unit tests also contribute to the rapid feedback principle. When writing code, the unit test provides direct feedback as to how the system reacts to the changes one has made. If, for instance, the changes affect a part of the system that is not in the scope of the programmer who made them, that programmer will not notice the flaw. There is a large chance that this bug will appear when the system is in production.

Assuming simplicity is about treating every problem as if its solution were "extremely simple". Traditional system development methods say to plan for the future and to code for reusability. Extreme programming rejects these ideas.

The advocates of Extreme Programming say that making big changes all at once does not work. Extreme Programming applies incremental changes: for example, a system might have small releases every three weeks. By making many little steps the customer has more control over the development process and the system that is being developed.

The principle of embracing change is about not working against changes but embracing them. For instance, if at one of the iterative meetings it appears that the customer's requirements have changed dramatically, programmers are to embrace this and plan the new requirements for the next iteration.

Activities

XP describes four basic activities that are performed within the software development process.

Coding

The advocates of XP argue that the only truly important product of the system development process is code (a concept to which they give a somewhat broader definition than might be given by others). Without code you have nothing.

Coding can be drawing diagrams that will generate code, scripting a web-based system or coding a program that needs to be compiled.

Coding can also be used to figure out the most suitable solution. For instance, XP would advocate that faced with several alternatives for a programming problem, one should simply code all solutions and determine with automated tests (discussed in the next section) which solution is most suitable.

Coding can also help to communicate thoughts about programming problems. A programmer dealing with a complex programming problem and finding it hard to explain the solution to fellow programmers might code it and use the code to demonstrate what he or she means. Code, say the exponents of this position, is always clear and concise and cannot be interpreted in more than one way. Other programmers can give feedback on this code by also coding their thoughts.

Testing

One cannot be certain of anything unless one has tested it. Testing is not a perceived, primary need for the customer. A lot of software is shipped without proper testing and still works (more or less). In software development, XP says this means that one cannot be certain that a function works unless one tests it. This raises the question of defining what one can be uncertain about. Software testing is the process used to measure the quality of developed computer software. ...

In computer programming, a unit test is a procedure used to validate that a particular module of source code is working properly. ... This article needs to be cleaned up to conform to a higher standard of quality. ...

Listening

Programmers do not necessarily know anything about the business side of the system under development. The function of the system is determined by the business side. For the programmers to find what the functionality of the system should be, they have to listen to business.

Programmers have to listen "in the large": they have to listen to what the customer needs. Also, they have to try to understand the business problem, and to give the customer feedback about his or her problem, to improve the customer's own understanding of his or her problem.

Communication between the customer and programmer is further addressed in The Planning Game.... Extreme Programming (XP) is a popular agile software development methodology used to implement software projects. ...

Designing

From the point of view of simplicity, one could say that system development doesn't need more than coding, testing and listening. If those activities are performed well, the result should always be a system that works. In practice, this will not work. One can come a long way without designing but at a given time one will get stuck. The system becomes too complex and the dependencies within the system cease to be clear. All Saints Chapel in the Cathedral Basilica of St. ...

One can avoid this by creating a design structure that organizes the logic in the system. Good design will avoid lots of dependencies within a system; this means that changing one part of the system will not affect other parts of the system.

Practices

Extreme Programming has 12 practices, grouped into four areas, derived from the best practices of software engineering: Extreme Programming (XP) is a popular agile software development methodology used to implement software projects. ... The term best practice generally refers to the best possible way of doing something; it is used in the fields of business management, software engineering, and medicine. ... Software engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software. ...

Continuous process Pair programming requires two software engineers to participate in a combined development effort at one workstation. ... Extreme Programming (XP) is a popular agile software development methodology used to implement software projects. ... Test-Driven Development (TDD) is a software development technique that involves repeatedly first writing a test case and then implementing only the code necessary to pass the test. ... Extreme Programming (XP) is a popular agile software development methodology used to implement software projects. ...

Shared understanding Continuous integration is the name that emerged in the Extreme Programming community for the software engineering practice of immediately committing every change, no matter how small, to a revision control system. ... Refactoring is the process of rewriting a computer program or other material to improve its structure or readability, while explicitly keeping its meaning or behavior. ...

Controversial aspects

Unstable Requirements: Proponents of Extreme Programming claim that by having the on-site customer request changes informally, the process becomes flexible, and saves the cost of formal overhead. Critics of XP claim this can lead to costly rework and project scope creep beyond what was previously agreed or funded. Rework is a term used in several contexts. ... It has been suggested that this article or section be merged into Mission creep. ...

User Conflicts: Change control boards are a sign that there are potential conflicts in project objectives and constraints between multiple users. XP's expedited methodology is somewhat dependent on programmers being able to assume a unified client viewpoint so the programmer can concentrate on coding rather than documentation of compromise objectives and constraints. This also applies when multiple programming organizations are involved, particularly organizations which compete for shares of projects.

Dependence upon all other aspects of XP: "XP is like a ring of poisonous snakes, daisy-chained together. All it takes is for one of them to wriggle loose, and you've got a very angry, poisonous snake heading your way." ^[3] Big Design Up Front (BDUF) is the (often criticized) idea in software development that a programs design should be completed and perfected before that programs implementation is started. ... A customer representative is an individual who represents a community that intends to purchase a product. ... A project is a temporary endeavor undertaken to create a unique product or service[1]. // The word project comes from the Latin word projectum from projicere, to throw something forwards which in turn comes from pro-, which denotes something that precedes the action of the next part of the word... Micro Management is the thirty third episode of the TV-series Danny Phantom. ...

Scalability: Opponents of XP claim that XP would only work on teams of twelve or fewer people. However, it has been claimed that XP has been used successfully on teams of over a hundred developers^{[citation needed]}. It is not that XP doesn't scale, just that few people have tried to scale it, and proponents of XP refuse to speculate on this facet of the process. ThoughtWorks has claimed reasonable success on distributed XP projects with up to sixty people. The current version of the article or section reads like an advertisement. ...

Controversy in Book: In 2003, Matt Stephens and Doug Rosenberg published a book under Apress called Extreme Programming Refactored: The Case Against XP which questioned the value of the XP process and suggested ways in which it could be improved. This triggered a lengthy debate in articles, internet newsgroups, and web-site chat areas. The core argument of the book is that XP's practices are interdependent but that few practical organizations are willing/able to adopt all the practices; therefore the entire process fails. The book also makes other criticisms and it draws a likeness of XP's "collective ownership" model to socialism in a negative manner. Socialism refers to a broad array of ideologies and movements which aim to improve society through collective and egalitarian action; and to a socio-economic system in which property and the distribution of wealth are subject to control by the community. ...

XP Evolution: Certain aspects of XP have changed since the book Extreme Programming Refactored (2003) was published; in particular, XP now accommodates modifications to the practices as long as the required objectives are still met. XP also uses increasingly generic terms for processes. Some argue that these changes invalidate previous criticisms; others claim that this is simply watering the process down.

In 2004 Industrial Extreme Programming (IXP) ^[4] was introduced as an evolution of XP. It brings ability to work in big and distributed teams. It now has 23 practices and flexible changeable values. As it is a new member of Agile family, there is not enough data to prove its usability, however it claims to be an answer to XP's imperfections.

Hybrid/Unified Methodologies: Other authors have tried to reconcile XP with the older methods in order to form a unified methodology. Some of these XP sought to replace, such as the waterfall method; example: Project Lifecycles: Waterfall, Rapid Application Development, and All That. The waterfall model is a sequential software development model (a process for the creation of software) 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. ...

JPMorgan Chase & Co. tried combining XP with the computer programming methodologies of Capability Maturity Model Integration (CMMI), and Six Sigma. They found that the three systems reinforced each other well, leading to better development, and did not mutually contradict, see Extreme Programming (XP) Six Sigma CMMI. JPMorgan Chase & Co. ... The Capability Maturity Model (CMM), first described by Watts Humphrey in his book Managing the Software Process (Addison Wesley Professional, Massachusetts, 1989), provides a process model based on software best-practices effective in large-scale, multi-person projects. ... The often-used six sigma symbol. ...

Finally, XP is not the only controversial methodology, because XP is a response to the controversy and criticisms about other methods used in software development.

Application of Extreme Programming

Controversial aspects notwithstanding, Extreme Programming remains a viable choice for some projects. Projects suited to Extreme Programming are those that:

Projects suited for more traditional methodologies are those that: It has been suggested that this article or section be merged with prototyping. ...

Project Managers must weigh project aspects against available methodologies to make an appropriate selection. However, some XP concepts could be applied outside, such as using Pair Programming to expedite related technical changes to the documentation set of a large project. // Summary Mission Critical is an adventure game released in 1995 by Legend Entertainment. ... A life-critical system or safety-critical system is a system whose failure or malfunction may result in a) death or serious injury to people, or b) loss or severe damage to equipment or c) environmental harm. ... In computer science, formal methods refers to a variety of scientific and engineering techniques for rigorous reasoning about the correctness of computer programs, chiefly based on the use of mathematical logic. ... Insurance, in law and economics, is a form of risk management primarily used to hedge against the risk of a contingent loss. ... A project manager is the person who has the overall responsibility for the successful planning and execution of any project. ...

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