In engineering Engineering is the discipline, art and profession of acquiring and applying technical, scientific, and mathematical knowledge to design and implement materials, structures, machines, devices, systems, and processes that safely realize a desired objective or invention, a requirement is a singular documented need of what a particular product or service should be or perform. It is most commonly used in a formal sense in systems engineering Systems engineering is an interdisciplinary field of engineering that focuses on how complex engineering projects should be designed and managed. Issues such as logistics, the coordination of different teams, and automatic control of machinery become more difficult when dealing with large, complex projects. Systems engineering deals with work- or software engineering Software engineering is a profession and field of study dedicated to designing, implementing, and modifying software so that it is of higher quality, more affordable, maintainable, and faster to build. The term software engineering first appeared in the 1968 NATO Software Engineering Conference, and was meant to provoke thought regarding the. It is a statement that identifies a necessary attribute, capability, characteristic, or quality of a system in order for it to have value and utility to a user.
In the classical engineering approach, sets of requirements are used as inputs into the design stages of product development In business and engineering, new product development is the term used to describe the complete process of bringing a new product or service to market. There are two parallel paths involved in the NPD process: one involves the idea generation, product design and detail engineering; the other involves market research and marketing analysis. Requirements are also an important input into the verification process, since tests should trace back to specific requirements. Requirements show what elements and functions are necessary for the particular project.
The requirements development phase may have been preceded by a feasibility study A feasibility study is an evaluation of a proposal designed to determine the difficulty in carrying out a designated task. Generally, a feasibility study precedes technical development and project implementation. In other words, a feasibility study is an evaluation or analysis of the potential impact of a proposed project, or a conceptual analysis phase of the project. The requirements phase may be broken down into requirements elicitation (gathering, understanding, reviewing, and articulating the needs of the stakeholders A corporate stakeholder is a party that can affect or be affected by the actions of the business as a whole. The stakeholder concept was first used in a 1963 internal memorandum at the Stanford Research institute. It defined stakeholders as "those groups without whose support the organization would cease to exist." The theory was later)[1], analysis Requirements analysis in systems engineering and software engineering, encompasses those tasks that go into determining the needs or conditions to meet for a new or altered product, taking account of the possibly conflicting requirements of the various stakeholders, such as beneficiaries or users (checking for consistency and completeness), specification (documenting the requirements) and validation (making sure the specified requirements are correct)[2][3].
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Product versus process requirements
Projects are subject to three sorts of requirements:
- Business requirements describe in business terms what must be delivered or accomplished to provide value.
- Product requirements describe properties of a system or product (which could be one of several ways to accomplish a set business requirements.)
- Process requirements describe activities performed by the developing organization. For instance, process requirements could specify specific methodologies to be followed, and constraints that the organization must obey.
Product and process requirements are closely linked. Process requirements often specify the activities that will be performed to satisfy a product requirement. For example, a maximum development cost requirement (a process requirement) may be imposed to help achieve a maximum sales price requirement (a product requirement); a requirement for the product to be maintainable (a Product requirement) often is addressed by imposing requirements to follow particular development styles (e.g., object-oriented programming Object-oriented programming is a programming paradigm that uses "objects" – data structures consisting of datafields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction, encapsulation, modularity, polymorphism, and), style-guides, or a review/inspection process (process requirements).
Requirements in systems and software engineering
In systems engineering, a requirement can be a description of what a system must do, referred to as a Functional Requirement In software engineering, a functional requirement defines a function of a software system or its component. A function is described as a set of inputs, the behavior, and outputs. This type of requirement specifies something that the delivered system must be able to do. Another type of requirement specifies something about the system itself, and how well it performs its functions. Such requirements are often called Non-functional requirements In systems engineering and requirements engineering, a non-functional requirement is a requirement that specifies criteria that can be used to judge the operation of a system, rather than specific behaviors. This should be contrasted with functional requirements that define specific behavior or functions, or 'performance requirements' or 'quality of service requirements.' Examples of such requirements include usability, availability, reliability, supportability, testability, maintainability, and (if defined in a way that's verifiably measurable and unambiguous) ease-of-use.
A collection of requirements define the characteristics or features of the desired system. A 'good' list of requirements generally avoids saying how the system should implement the requirements, leaving such decisions to the system designer. Describing how the system should be implemented may be known as implementation bias or "solution engineering". However, implementation constraints (aka solution requirements) on the solution may be validly expressed by the future owner, for example for communality reasons with other owned products.
In software engineering, the same meanings of requirements apply, except that the focus of interest is the software itself.
Product requirements
Types of product requirements
Requirements are typically placed into these categories:
- Functional requirements In software engineering, a functional requirement defines a function of a software system or its component. A function is described as a set of inputs, the behavior, and outputs describe the functionality that the system is to execute; for example, formatting some text or modulating a signal. They are sometimes known as capabilities.
- Non-functional requirements In systems engineering and requirements engineering, a non-functional requirement is a requirement that specifies criteria that can be used to judge the operation of a system, rather than specific behaviors. This should be contrasted with functional requirements that define specific behavior or functions are the ones that act to constrain the solution. Nonfunctional requirements are sometimes known as quality requirements or ilities Within systems engineering, quality attributes are non-functional requirements used to evaluate the performance of a system. These are sometimes named "ilities" after the suffix many of the words share. Notable quality attributes include:.
- Constraint requirements are the ones that act to constrain the solution. No matter how the problem is solved the constraint requirements must be adhered to.
Non-functional requirements can be further classified according to whether they are usability requirements, look and feel requirements, humanity requirements, performance requirements, maintainability requirements, operational requirements, safety requirements, reliability requirements, or one of many other types of requirements.
In software engineering Software engineering is a profession and field of study dedicated to designing, implementing, and modifying software so that it is of higher quality, more affordable, maintainable, and faster to build. The term software engineering first appeared in the 1968 NATO Software Engineering Conference, and was meant to provoke thought regarding the this categorization is useful because only functional requirements can be directly implemented in software. The non-functional requirements are controlled by other aspects of the system. For example, in a computer system reliability is related to hardware failure rates, and performance is controlled by CPU and memory. Non-functional requirements can in some cases be decomposed into functional requirements for software. For example, a system level non-functional safety requirement can be decomposed into one or more functional requirements. See FURPS. In addition, a non-functional requirement may be converted into a process requirement when the requirement is not easily measurable. For example, a system level maintainability requirement may be decomposed into restrictions on software constructs or limits on lines or code.
Characteristics of good requirements
The characteristics of good requirements are variously stated by different writers, with each writer generally emphasizing the characteristics most appropriate to their general discussion or the specific technology domain being addressed. However, the following characteristics are generally acknowledged[4].
| Characteristic | Explanation |
|---|---|
| Unitary (Cohesive) | The requirement addresses one and only one thing. |
| Complete | The requirement is fully stated in one place with no missing information. |
| Consistent | The requirement does not contradict any other requirement and is fully consistent with all authoritative external documentation. |
| Non-Conjugated (Atomic) | The requirement is atomic, i.e., it does not contain conjunctions. E.g., "The postal code field must validate American and Canadian postal codes" should be written as two separate requirements: (1) "The postal code field must validate American postal codes" and (2) "The postal code field must validate Canadian postal codes". |
| Traceable | The requirement meets all or part of a business need as stated by stakeholders and authoritatively documented. |
| Current | The requirement has not been made obsolete by the passage of time. |
| Feasible | The requirement can be implemented within the constraints of the project. |
| Unambiguous | The requirement is concisely stated without recourse to technical jargon, acronyms (unless defined elsewhere in the Requirements document), or other esoteric verbiage. It expresses objective facts, not subjective opinions. It is subject to one and only one interpretation. Vague subjects, adjectives, prepositions, verbs and subjective phrases are avoided. Negative statements and compound statements are prohibited. |
| Mandatory | The requirement represents a stakeholder-defined characteristic the absence of which will result in a deficiency that cannot be ameliorated. An optional requirement is a contradiction in terms. |
| Verifiable | The implementation of the requirement can be determined through one of four possible methods: inspection, demonstration, test or analysis. |
To the above some add Externally Observable, that is, the requirement specifies a characteristic of the product that is externally observable or experienced by the user. Such advocates argue that requirements that specify internal architecture, design, implementation, or testing decisions are probably constraints, and should be clearly articulated in the Constraints section of the Requirements document. The contrasting view is that this perspective fails on two points. First, the perspective does not recognize that the user experience may be supported by requirements not perceivable by the user. For example, a requirement to present geocoded Geocoding is the process of finding associated geographic coordinates from other geographic data, such as street addresses, or zip codes (postal codes). With geographic coordinates the features can be mapped and entered into Geographic Information Systems, or the coordinates can be embedded into media such as digital photographs via geotagging information to the user may be supported by a requirement for an interface with an external third party business partner. The interface will be imperceptible to the user, though the presentation of information obtained through the interface certainly would not. Second, a constraint limits design alternatives, whereas a requirement specifies design characteristics. To continue the example, a requirement selecting a web service interface is different from a constraint limiting design alternatives to methods compatible with a Single Sign-On architecture.
Verification
All requirements should be verifiable. The most common method is by test. If this is not the case, another verification method should be used instead (e.g. analysis, demonstration or inspection or review of design).
Certain requirements, by their very structure, are not verifiable. These include requirements that say the system shall never or always exhibit a particular property. Proper testing of these requirements would require an infinite testing cycle. Such requirements must be rewritten to be verifiable. As stated above all requirements must be verifiable.
Non-functional requirements, which are unverifiable at the software level, must still be kept as a documentation of customer intent; however they may traced to process requirements that are determined to be a practical way of meeting them. For example, a non-functional requirement to be free from backdoors A backdoor in a computer system is a method of bypassing normal authentication, securing remote access to a computer, obtaining access to plaintext, and so on, while attempting to remain undetected. The backdoor may take the form of an installed program (e.g., Back Orifice), or could be a modification to an existing program or hardware device may be satisfied by replacing it with a process requirement to use pair programming. Other non-functional requirements will trace to other system components and be verified at that level. For example system reliability is often verified by analysis at the system level. Avionics software Avionics software is embedded software with legally-mandated safety and reliability concerns used in avionics. The main difference between avionic software and conventional embedded software is that the development process is required by law and is optimized for safety with its complicated safety requirements must follow the DO-178B DO-178B, Software Considerations in Airborne Systems and Equipment Certification is the title of a document published by RTCA, Incorporated. Development was a joint effort with EUROCAE. When specified by the Technical Standard Order for which certification is sought, the FAA applies DO-178B as the document it uses for guidance to determine if the development process.
Verifiability is necessary for a requirement but there are other important issues. A requirement can be verifiable yet incorrect; and assessing verifiability alone will not detect incorrect requirements. Moreover, verification is totally irrelevant with regard to a requirement which has been overlooked. Mere analysis, inspection, or review alone will find some of these issues but generally is far weaker than usually is realized.
Requirements analysis or requirements engineering
Main article: Requirements analysis Requirements analysis in systems engineering and software engineering, encompasses those tasks that go into determining the needs or conditions to meet for a new or altered product, taking account of the possibly conflicting requirements of the various stakeholders, such as beneficiaries or usersRequirements are prone to issues of ambiguity, incompleteness, and inconsistency. Techniques such as rigorous inspection Inspection in software engineering, refers to peer review of any work product by trained individuals who look for defects using a well defined process. An inspection might also be referred to as a Fagan inspection after Michael Fagan, the inventor of the process have been shown to help deal with these issues. Ambiguities, incompleteness, and inconsistencies that can be resolved in the requirements phase typically cost orders of magnitude less to correct than when these same issues are found in later stages of product development. Requirements analysis strives to address these issues.
There is an engineering trade off to consider between requirements which are too vague, and those which are so detailed that they
- take a long time to produce - sometimes to the point of being obsolete once completed
- limit the implementation options available
- are costly to produce
Documenting requirements
Requirements are usually written as a means for communication between the different stakeholders. This means that the requirements should be easy to understand both for normal users and for developers. One common way to document a requirement is stating what the system shall do. Example: 'The contractor shall deliver the product no later than xyz date.' Other ways include use cases and user stories.
Changes in requirements
Requirements generally change with time. Once defined and approved, requirements should fall under change control Change control within Quality management systems and Information Technology (IT) systems is a formal process used to ensure that changes to a product or system are introduced in a controlled and coordinated manner. It reduces the possibility that unnecessary changes will be introduced to a system without forethought, introducing faults into the. For many projects, requirements are altered before the system is complete. This is partly due to the complexity of computer software and the fact that users don't know what they want before they see it. This characteristic of requirements has led to requirements management Requirements management is the process of identifying, eliciting, documenting, analyzing, tracing, prioritizing and agreeing on requirements and then controlling change and communicating to relevant stakeholders. It is a continuous process throughout a project. A requirement is a capability to which a project outcome should conform studies and practices.
Disputes regarding the necessity of rigour in software requirements
Most agile software development 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 methodologies question the need for rigorously describing software requirements upfront, which they consider a moving target. Instead, extreme programming Extreme Programming is a software development methodology which is 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 (timeboxing), which is intended to improve productivity and introduce for example describes requirements informally using user stories A user story is a software system requirement formulated as one or two sentences in the everyday or business language of the user. User stories are used with Agile software development methodologies for the specification of requirements . Each user story is limited, so it fits on a small paper note card—usually a 3×5 inches card—to ensure (short summaries fitting on an index card explaining one aspect of what the system should do), and considers it the developer's duty to directly ask the customer for clarification. Agile methodologies also typically capture requirements in a series of automated acceptance test.
See also
- FURPS - acronym of key requirement categories
- Requirements analysis Requirements analysis in systems engineering and software engineering, encompasses those tasks that go into determining the needs or conditions to meet for a new or altered product, taking account of the possibly conflicting requirements of the various stakeholders, such as beneficiaries or users
- Requirements management Requirements management is the process of identifying, eliciting, documenting, analyzing, tracing, prioritizing and agreeing on requirements and then controlling change and communicating to relevant stakeholders. It is a continuous process throughout a project. A requirement is a capability to which a project outcome should conform
- Requirement prioritization
- Requirements traceability Requirements traceability is a sub-discipline of requirements management within software development and systems engineering. Requirements traceability is concerned with documenting the life of a requirement. It may be possible to find the origin of each requirement and track every change which was made to this requirement. For this purpose, it
- Specification (technical standard) A specification is an explicit set of requirements to be satisfied by a material, product, or service. Should a material, product or service fail to meet one or more of the applicable specifications, it may be referred to as being out of specification; the abbreviation OOS may also be used
- Use case A use case in software engineering and systems engineering is a description of a system’s behavior as it responds to a request that originates from outside of that system. In other words, a use case describes "who" can do "what" with the system in question. The use case technique is used to capture a system's behavioral
References
- ^ Stellman, Andrew; Greene, Jennifer (2005). Applied Software Project Management. O'Reilly Media. p. 98. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 978-0-596-00948-9. http://www.stellman-greene.com/aspm/.
- ^ Wiegers, Karl E. (2003). Software Requirements, Second Edition. Microsoft Press. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0-7356-1879-8.
- ^ Young, Ralph R. (2001). Effective Requirements Practices. Addison-Wesley. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 978-0201709124.
- ^ Davis, Alan M. (1993). Software Requirements: Objects, Functions, and States, Second Edition. Prentice Hall. ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 0-13-805763-X.
External links
- Discovering System Requirements
- The International Institute for Business Analysis and The IIBA's Business Analysis Body of Knowledge
- Writing Good Requirements
Categories: Software requirements
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Q. I have been looking for a website to order a few baby chickens from but all I have found are sites that have a minimum requirement of 15-25 chicks that i do not have room for. Can someone provide a website that sells chicks without the requirement?
Asked by sally_dood - Mon May 5 09:34:24 2008 - - 2 Answers - 0 Comments
A. There are some hatcheries that will ship small orders but the fee is more than the price of the chickens. I don't remember which hatcheries will do this. If a local feed or farm store is ordering chickens you can buy as many or as few as you want. Another option is to find a friend who wants a few chickens and combine your order. Around here the Tractor Supply Company gets chicks every Thursday and you can buy as many as you want from their stock. They usually sell out on Friday. Another option is to order 15 chicks. Keep a few and sell the rest. You can start advertising them before you get them. Just tell interested buyers they will be available when they arrive.
Answered by winterrules - Mon May 5 18:13:52 2008
