Lean software development is a translation of lean manufacturing principles and practices to the software development domain. Adapted from the Toyota Production System,[1] it is emerging with the support of a pro-lean subculture within the agile community. Lean offers a solid conceptual framework, values and principles, as well as good practices, derived from experience, that support agile organizations.
The expression "lean software development" originated in a book by the same name, written by Mary Poppendieck and Tom Poppendieck in 2003.[2] The book restates traditional lean principles, as well as a set of 22 tools and compares the tools to corresponding agile practices. The Poppendiecks' involvement in the agile software development community, including talks at several Agile conferences [3] has resulted in such concepts being more widely accepted within the agile community.
Lean principles
Lean development can be summarized by seven principles, very close in concept to lean manufacturing principles:[4]
In order to eliminate waste, one should be able to recognize it. If some activity could be bypassed or the result could be achieved without it, it is waste. Partially done coding eventually abandoned during the development process is waste. Extra features like paperwork and features not often used by customers are waste. Switching people between tasks is waste (because of time spent, and often lost, by people involved in context-switching). Waiting for other activities, teams, processes is waste. Relearning requirements to complete work is waste. Defects and lower quality are waste. Managerial overhead not producing real value is waste.
A value stream mapping technique is used to identify waste. The second step is to point out sources of waste and to eliminate them. Waste-removal should take place iteratively until even seemingly essential processes and procedures are liquidated.
Amplify learning
Software development is a continuous learning process based on iterations when writing code. Software design is a problem-solving process involving the developers writing the code and what they have learned. Software value is measured in fitness for use and not in conformance to requirements.
Instead of adding more documentation or detailed planning, different ideas could be tried by writing code and building. The process of user requirements gathering could be simplified by presenting screens to the end-users and getting their input. The accumulation of defects should be prevented by running tests as soon as the code is written.
The learning process is sped up by usage of short iteration cycles – each one coupled with refactoring and integration testing. Increasing feedback via short feedback sessions with customers helps when determining the current phase of development and adjusting efforts for future improvements. During those short sessions, both customer representatives and the development team learn more about the domain problem and figure out possible solutions for further development. Thus the customers better understand their needs, based on the existing result of development efforts, and the developers learn how to better satisfy those needs. Another idea in the communication and learning process with a customer is set-based development – this concentrates on communicating the constraints of the future solution and not the possible solutions, thus promoting the birth of the solution via dialogue with the customer.[jargon]
Decide as late as possible
As software development is always associated with some uncertainty, better results should be achieved with a set-based or options-based approach, delaying decisions as much as possible until they can be made based on facts and not on uncertain assumptions and predictions. The more complex a system is, the more capacity for change should be built into it, thus enabling the delay of important and crucial commitments. The iterative approach promotes this principle – the ability to adapt to changes and correct mistakes, which might be very costly if discovered after the release of the system.
With set-based development: If a new brake system is needed for a car, for example, three teams may design solutions to the same problem. Each team learns about the problem space and designs a potential solution. As a solution is deemed unreasonable, it is cut. At the end of a period, the surviving designs are compared and one is chosen, perhaps with some modifications based on learning from the others - a great example of deferring commitment until the last possible moment. Software decisions could also benefit from this practice to minimize the risk brought on by big up-front design. Additionally, there would then be multiple implementations that work correctly, yet are different (implementation-wise, internally). These could be used to implement fault-tolerant systems which check all inputs and outputs for correctness, across the multiple implementations, simultaneously.
An agile software development approach can move the building of options earlier for customers, thus delaying certain crucial decisions until customers have realized their needs better. This also allows later adaptation to changes and the prevention of costly earlier technology-bounded decisions. This does not mean that no planning should be involved – on the contrary, planning activities should be concentrated on the different options and adapting to the current situation, as well as clarifying confusing situations by establishing patterns for rapid action. Evaluating different options is effective as soon as it is realized that they are not free, but provide the needed flexibility for late decision making.
Deliver as fast as possible
In the era of rapid technology evolution, it is not the biggest that survives, but the fastest. The sooner the end product is delivered without major defects, the sooner feedback can be received, and incorporated into the next iteration. The shorter the iterations, the better the learning and communication within the team. With speed, decisions can be delayed. Speed assures the fulfilling of the customer's present needs and not what they required yesterday. This gives them the opportunity to delay making up their minds about what they really require until they gain better knowledge. Customers value rapid delivery of a quality product.
The just-in-time production ideology could be applied to software development, recognizing its specific requirements and environment. This is achieved by presenting the needed result and letting the team organize itself and divide the tasks for accomplishing the needed result for a specific iteration. At the beginning, the customer provides the needed input. This could be simply presented in small cards or stories – the developers estimate the time needed for the implementation of each card. Thus the work organization changes into self-pulling system – each morning during a stand-up meeting, each member of the team reviews what has been done yesterday, what is to be done today and tomorrow, and prompts for any inputs needed from colleagues or the customer. This requires transparency of the process, which is also beneficial for team communication.
The myth underlying this principle is haste makes waste. However, lean implementation has shown that it is a good practice to deliver fast in order to see and analyze the output as early as possible.
Empower the team
There has been a traditional belief in most businesses about the decision-making in the organization – the managers tell the workers how to do their own job. In a work-out technique, the roles are turned – the managers are taught how to listen to the developers, so they can explain better what actions might be taken, as well as provide suggestions for improvements. The lean approach follows the agile principle[6] "build projects around motivated individuals [...] and trust them to get the job done",[7] encouraging progress, catching errors, and removing impediments, but not micro-managing.
Another mistaken belief has been the consideration of people as resources. People might be resources from the point of view of a statistical data sheet, but in software development, as well as any organizational business, people do need something more than just the list of tasks and the assurance that they will not be disturbed during the completion of the tasks. People need motivation and a higher purpose to work for – purpose within the reachable reality, with the assurance that the team might choose its own commitments. The developers should be given access to the customer; the team leader should provide support and help in difficult situations, as well as ensure that skepticism does not ruin the team's spirit. Respecting people and acknowledging their work is one way to empower the team.
Build integrity in
The customer needs to have an overall experience of the system. This is the so-called perceived integrity: how it is being advertised, delivered, deployed, accessed, how intuitive its use is, its price and how well it solves problems.
Conceptual integrity means that the system's separate components work well together as a whole with balance between flexibility, maintainability, efficiency, and responsiveness. This could be achieved by understanding the problem domain and solving it at the same time, not sequentially. The needed information is received in small batch pieces – not in one vast chunk - preferably by face-to-face communication and not any written documentation. The information flow should be constant in both directions – from customer to developers and back, thus avoiding the large stressful amount of information after long development in isolation.
One of the healthy ways towards integral architecture is refactoring. As more features are added to the original code base, the harder it becomes to add further improvements. Refactoring is about keeping simplicity, clarity, minimum number of features in the code. Repetitions in the code are signs of bad code designs and should be avoided (i.e. by applying the DRY rule). The complete and automated building process should be accompanied by a complete and automated suite of developer and customer tests, having the same versioning, synchronization and semantics as the current state of the system. At the end the integrity should be verified with thorough testing, thus ensuring the System does what the customer expects it to. Automated tests are also considered part of the production process, and therefore if they do not add value they should be considered waste. Automated testing should not be a goal, but rather a means to an end, specifically the reduction of defects.
Optimize the whole
Modern software systems are not simply the sum of their parts, but also the product of their interactions. Defects in software tend to accumulate during the development process – by decomposing the big tasks into smaller tasks, and by standardizing different stages of development, the root causes of defects should be found and eliminated. The larger the system, the more organizations that are involved in its development and the more parts are developed by different teams, the greater the importance of having well defined relationships between different vendors, in order to produce a system with smoothly interacting components. During a longer period of development, a stronger subcontractor network is far more beneficial than short-term profit optimizing, which does not enable win-win relationships.
Lean thinking has to be understood well by all members of a project, before implementing in a concrete, real-life situation. "Think big, act small, fail fast; learn rapidly"[8] – these slogans summarize the importance of understanding the field and the suitability of implementing lean principles along the whole software development process. Only when all of the lean principles are implemented together, combined with strong "common sense" with respect to the working environment, is there a basis for success in software development.
Lean software practices
Lean software development practices, or what the Poppendiecks call "tools" are restated slightly from the original equivalents in agile software development. Examples of such practices include:
Since agile software development is an umbrella term for a set of methods and practices based on the values and principles expressed in the Agile Manifesto, lean software development is considered an agile software development method.[9]
Test-driven development (TDD) is a way of writing code that involves writing an automated unit-level test case that fails, then writing just enough code to make the test pass, then refactoring both the test code and the production code, then repeating with another new test case.
Agile software development is the mindset for developing software that derives from values agreed upon by The Agile Alliance, a group of 17 software practitioners in 2001. As documented in their Manifesto for Agile Software Development the practitioners value:
Dynamic systems development method (DSDM) is an agile project delivery framework, initially used as a software development method. First released in 1994, DSDM originally sought to provide some discipline to the rapid application development (RAD) method. In later versions the DSDM Agile Project Framework was revised and became a generic approach to project management and solution delivery rather than being focused specifically on software development and code creation and could be used for non-IT projects. The DSDM Agile Project Framework covers a wide range of activities across the whole project lifecycle and includes strong foundations and governance, which set it apart from some other Agile methods. The DSDM Agile Project Framework is an iterative and incremental approach that embraces principles of Agile development, including continuous user/customer involvement.
"You aren't gonna need it" (YAGNI) is a principle which arose from extreme programming (XP) that states a programmer should not add functionality until deemed necessary. Other forms of the phrase include "You aren't going to need it" (YAGTNI) and "You ain't gonna need it".
In agile principles, timeboxing allocates a maximum unit of time to an activity, called a timebox, within which a planned activity takes place. It is used by agile principles-based project management approaches and for personal time management.
Genba is a Japanese term meaning "the actual place". Japanese detectives call the crime scene genba, and Japanese TV reporters may refer to themselves as reporting from genba. In business, genba refers to the place where value is created; in manufacturing, the genba is the factory floor. It can be any "site" such as a construction site, sales floor or where the service provider interacts directly with the customer.
Extreme programming (XP) is an agile software development methodology used to implement software systems. This article details the practices used in this methodology. Extreme programming has 12 practices, grouped into four areas, derived from the best practices of software engineering.
Scrum is an agile team collaboration framework commonly used in software development and other industries.
Lean IT is the extension of lean manufacturing and lean services principles to the development and management of information technology (IT) products and services. Its central concern, applied in the context of IT, is the elimination of waste, where waste is work that adds no value to a product or service.
The INVEST mnemonic for Agile software development projects was created by Bill Wake as a reminder of the characteristics of a good quality Product Backlog Item or PBI for short. Such PBIs may be used in a Scrum backlog, Kanban board or XP project.
Lean project management is the application of lean concepts such as lean construction, lean manufacturing and lean thinking to project management.
Lean integration is a management system that emphasizes creating value for customers, continuous improvement, and eliminating waste as a sustainable data integration and system integration practice. Lean integration has parallels with other lean disciplines such as lean manufacturing, lean IT, and lean software development. It is a specialized collection of tools and techniques that address the unique challenges associated with seamlessly combining information and processes from systems that were independently developed, are based on incompatible data models, and remain independently managed, to achieve a cohesive holistic operation.
Kanban is a lean method to manage and improve work across human systems. This approach aims to manage work by balancing demands with available capacity, and by improving the handling of system-level bottlenecks.
A kanban board is one of the tools that can be used to implement kanban to manage work at a personal or organizational level.
Extreme programming (XP) is a software development methodology intended to improve software quality and responsiveness to changing customer requirements. As a type of agile software development, it advocates frequent releases in short development cycles, intended to improve productivity and introduce checkpoints at which new customer requirements can be adopted.
Disciplined agile delivery (DAD) is the software development portion of the Disciplined Agile Toolkit. DAD enables teams to make simplified process decisions around incremental and iterative solution delivery. DAD builds on the many practices espoused by advocates of agile software development, including scrum, agile modeling, lean software development, and others.
Scrumban is an Agile aligned approach to product delivery which is a hybrid of Scrum and Kanban. Scrumban was originally designed as a way to transition from Scrum to Kanban.
The scaled agile framework (SAFe) is a set of organization and workflow patterns intended to guide enterprises in scaling lean and agile practices. Along with disciplined agile delivery (DAD) and S@S (Scrum@Scale), SAFe is one of a growing number of frameworks that seek to address the problems encountered when scaling beyond a single team.
Evolutionary database design involves incremental improvements to the database schema so that it can be continuously updated with changes, reflecting the customer's requirements. People across the globe work on the same piece of software at the same time hence, there is a need for techniques that allow a smooth evolution of database as the design develops. Such methods utilize automated refactoring and continuous integration so that it supports agile methodologies for software development. These development techniques are applied on systems that are in pre-production stage as well on systems that have already been released. These techniques not only cover relevant changes in the database schema according to customer's changing needs, but also migration of modified data into the database and also customizing the database access code accordingly without changing the data semantics.
Agile architecture means how enterprise architects, system architects and software architects apply architectural practice in agile software development. A number of commentators have identified a tension between traditional software architecture and agile methods along the axis of adaptation versus anticipation.
References
↑ Yasuhiro Monden (1998), Toyota Production System, An Integrated Approach to Just-In-Time, Third edition, Norcross, GA: Engineering & Management Press, ISBN0-412-83930-X.
Ries, Eric (September 2011). The Lean Startup: How Today's Entrepreneurs Use Continuous Innovation to Create Radically Successful Businesses. Crown Business. ISBN978-0307887894.
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