Functional specification
Encyclopedia
A functional specification (also, functional spec, specs, functional specifications document (FSD), functional requirements specification, or Program specification) in systems engineering
Systems engineering
Systems engineering is an interdisciplinary field of engineering that focuses on how complex engineering projects should be designed and managed over the life cycle of the project. Issues such as logistics, the coordination of different teams, and automatic control of machinery become more...
and software development
Software development
Software development is the development of a software product...
is the documentation that describes the requested behavior of an engineering system. The documentation typically describes what is needed by the system user as well as requested properties of inputs and outputs (e.g. of the software system).
Overview
In systems engineeringSystems engineering
Systems engineering is an interdisciplinary field of engineering that focuses on how complex engineering projects should be designed and managed over the life cycle of the project. Issues such as logistics, the coordination of different teams, and automatic control of machinery become more...
a specification is a document that clearly and accurately describes the essential technical requirements for items, materials, or services including the procedures by which it can be determined that the requirements have been met. Specifications help avoid duplication and inconsistencies, allow for accurate estimates of necessary work and resources, act as a negotiation and reference document for engineering changes, provide documentation of configuration, and allow for consistent communication among those responsible for the eight primary functions of Systems Engineering. They provide a precise idea of the problem to be solved so that they can efficiently design the system and estimate the cost of design alternatives. They provide guidance to testers for verification (qualification) of each technical requirement.
A functional
Function (engineering)
In engineering, a function is interpreted as a specific process, action or task that a system is able to perform .-In engineering design:In the lifecycle of engineering projects, there are usually distinguished subsequently: Requirements and Functional specification documents. The Requirements...
specification does not define the inner workings of the proposed system; it does not include the specification how the system function will be implemented. Instead, it focuses on what various outside agents (people using the program, computer peripherals, or other computers, for example) might "observe" when interacting with the system. A typical functional specification might state the following:
- When the user clicks the OK button, the dialog is closed and the focus is returned to the main window in the state it was in before this dialog was displayed.
Such a requirement describes an interaction between an external agent (the user
User (computing)
A user is an agent, either a human agent or software agent, who uses a computer or network service. A user often has a user account and is identified by a username , screen name , nickname , or handle, which is derived from the identical Citizen's Band radio term.Users are...
) and the software system. When the user provides input to the system by clicking the OK button, the program responds (or should respond) by closing the dialog window containing the OK button.
It can be informal, in which case it can be considered as a blueprint
Blueprint
A blueprint is a type of paper-based reproduction usually of a technical drawing, documenting an architecture or an engineering design. More generally, the term "blueprint" has come to be used to refer to any detailed plan....
or user manual from a developer point of view, or formal
Formal specification
In computer science, a formal specification is a mathematical description of software or hardware that may be used to develop an implementation. It describes what the system should do, not how the system should do it...
, in which case it has a definite meaning defined in mathematical
Mathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
or programmatic terms. In practice, most successful specifications are written to understand and fine-tune applications that were already well-developed, although safety-critical software systems are often carefully specified prior to application development. Specifications are most important for external interfaces that must remain stable.
Purpose
There are many purposes for functional specifications. One of the primary purposes on team projects is to achieve some form of team consensus on what the program is to achieve before making the more time-consuming effort of writing source codeSource code
In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...
and test case
Test case
A test case in software engineering is a set of conditions or variables under which a tester will determine whether an application or software system is working correctly or not. The mechanism for determining whether a software program or system has passed or failed such a test is known as a test...
s, followed by a period of debugging
Debugging
Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge...
. Typically, such consensus is reached after one or more reviews by the stakeholders on the project at hand after having negotiated a cost-effective way to achieve the requirements the software needs to fulfill.
Process
In the ordered industrial software engineering life-cycle (waterfall modelWaterfall model
The waterfall model is a sequential design process, often used in software development processes, in which progress is seen as flowing steadily downwards through the phases of Conception, Initiation, Analysis, Design, Construction, Testing, Production/Implementation and Maintenance.The waterfall...
), functional specification describes what has to be implemented. The next system specification document describes how the functions will be realized using a chosen software environment. In not industrial, prototypical systems development, functional specifications are typically written after or as part of requirements analysis
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...
.
When the team agrees that functional specification consensus is reached, the functional spec is typically declared "complete" or "signed off". After this, typically the software development and testing team write source code and test cases using the functional specification as the reference. While testing is performed the behavior of the program is compared against the expected behavior as defined in the functional specification.
Types of software development specifications
- Advanced Microcontroller Bus ArchitectureAdvanced Microcontroller Bus ArchitectureThe Advanced Microcontroller Bus Architecture is used as the on-chip bus in system-on-a-chip designs. Since its inception, the scope of AMBA has gone far beyond microcontroller devices, and is now widely used on a range of ASIC and SoC parts including applications processors used in modern...
- Bit specification (disambiguation)
- Design specificationDesign specificationA design specification provides explicit information about the requirements for a product and how the product is to be put together. It is the most traditional kind of specification, having been used historically in public contracting for buildings, highways, and other public works, and represents...
- Diagnostic design specificationDiagnostic design specificationDiagnostic design specification is a document indicating how the diagnostics will be implemented on an upcoming/new products that will be developed by the company. It describes the behavior of the diagnostics like how the test will execute, how the output messages are formatted, and how the final...
- Multiboot SpecificationMultiboot SpecificationThe Multiboot Specification is an open standard originally created in 1995 and developed by the Free Software Foundation. The specification describes a method of loading various multiboot kernels using a single compliant boot loader. GNU Hurd, VMware ESXi, Xen, and L4 microkernels all need to be...
- Product design specificationProduct design specificationA product design specification is a statement of what a not-yet-designed product is intended to do. Its aim is to ensure that the subsequent design and development of a product meets the needs of the user. Product design specification is one of the elements of product lifecycle management.The PDS...
- Real-time specification for Java
- Software Requirements SpecificationSoftware Requirements Specification-Organization of an SRS:A Software Requirements Specification – a requirements specification for a software system – is a complete description of the behavior of a system to be developed. It includes a set of use cases that describe all the interactions the users will have with the software. In...
See also
- BenchmarkingBenchmarkingBenchmarking is the process of comparing one's business processes and performance metrics to industry bests and/or best practices from other industries. Dimensions typically measured are quality, time and cost...
- Benchmark specification
- Extensible Firmware InterfaceExtensible Firmware InterfaceThe Unified Extensible Firmware Interface is a specification that defines a software interface between an operating system and platform firmware...
- Software development processSoftware development processA software development process, also known as a software development life cycle , is a structure imposed on the development of a software product. Similar terms include software life cycle and software process. It is often considered a subset of systems development life cycle...
- Specification (technical standard)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...
- Single UNIX SpecificationSingle UNIX SpecificationThe Single UNIX Specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"...
- Verification and Validation (software)