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In science, computing, and engineering, a black box is a system which can be viewed in terms of its inputs and outputs (or transfer characteristics), without any knowledge of its internal workings. Its implementation is "opaque" (black). The term can be used to refer to many inner workings, such as those of a
transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...
, an
engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...
, an
algorithm In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing ...
, the
human brain The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of ...
, or an institution or government. To analyse an open system with a typical "black box approach", only the behavior of the stimulus/response will be accounted for, to infer the (unknown) ''box''. The usual representation of this ''black box system'' is a
data flow diagram A data-flow diagram is a way of representing a flow of data through a process or a system (usually an information system). The DFD also provides information about the outputs and inputs of each entity and the process itself. A data-flow diagram h ...
centered in the box. The opposite of a black box is a system where the inner components or logic are available for inspection, which is most commonly referred to as a white box (sometimes also known as a "clear box" or a "glass box").


History

The modern meaning of the term "black box" seems to have entered the English language around 1945. In electronic circuit theory the process of network synthesis from
transfer function In engineering, a transfer function (also known as system function or network function) of a system, sub-system, or component is a mathematical function that theoretically models the system's output for each possible input. They are widely used ...
s, which led to electronic circuits being regarded as "black boxes" characterized by their response to signals applied to their
ports A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as H ...
, can be traced to
Wilhelm Cauer Wilhelm Cauer (24 June 1900 – 22 April 1945) was a German mathematician and scientist. He is most noted for his work on the analysis and synthesis of electrical filters and his work marked the beginning of the field of network synthesis. Prior ...
who published his ideas in their most developed form in 1941. Although Cauer did not himself use the term, others who followed him certainly did describe the method as black-box analysis.
Vitold Belevitch Vitold Belevitch (2 March 1921 – 26 December 1999) was a Belgian mathematician and electrical engineer of Russian origin who produced some important work in the field of electrical network theory. Born to parents fleeing the Bolsheviks, he ...
puts the concept of black-boxes even earlier, attributing the explicit use of
two-port network A two-port network (a kind of four-terminal network or quadripole) is an electrical network ( circuit) or device with two ''pairs'' of terminals to connect to external circuits. Two terminals constitute a port if the currents applied to them sat ...
s as black boxes to Franz Breisig in 1921 and argues that 2-terminal components were implicitly treated as black-boxes before that. In
cybernetics Cybernetics is a wide-ranging field concerned with circular causality, such as feedback, in regulatory and purposive systems. Cybernetics is named after an example of circular causal feedback, that of steering a ship, where the helmsperson ma ...
, a full treatment was given by Ross Ashby in 1956.Ashby, W. Ross; ''An introduction to cybernetics'', London: Chapman & Hall, 1956, chapter 6: ''The black box'', pp. 86117. A black box was described by
Norbert Wiener Norbert Wiener (November 26, 1894 – March 18, 1964) was an American mathematician and philosopher. He was a professor of mathematics at the Massachusetts Institute of Technology (MIT). A child prodigy, Wiener later became an early researcher ...
in 1961 as an unknown system that was to be identified using the techniques of
system identification The field of system identification uses statistical methods to build mathematical models of dynamical systems from measured data. System identification also includes the optimal design of experiments for efficiently generating informative dat ...
. He saw the first step in
self-organization Self-organization, also called spontaneous order in the social sciences, is a process where some form of overall order arises from local interactions between parts of an initially disordered system. The process can be spontaneous when suffic ...
as being to be able to copy the output behavior of a black box. Many other engineers, scientists and epistemologists, such as
Mario Bunge Mario Augusto Bunge (; ; September 21, 1919 – February 24, 2020) was an Argentine-Canadian philosopher and physicist. His philosophical writings combined scientific realism, systemism, materialism, emergentism, and other principles. He was ...
, used and perfected the black box theory in the 1960s.


System theory

In
systems theory Systems theory is the interdisciplinary study of systems, i.e. cohesive groups of interrelated, interdependent components that can be natural or human-made. Every system has causal boundaries, is influenced by its context, defined by its structu ...
, the ''black box'' is an abstraction representing a class of concrete open system which can be viewed solely in terms of its ''stimuli inputs'' and ''output reactions'': The understanding of a ''black box'' is based on the "explanatory principle", the
hypothesis A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...
of a
causal relation In mathematical physics, the causal structure of a Lorentzian manifold describes the causal relationships between points in the manifold. Introduction In modern physics (especially general relativity) spacetime is represented by a Lorentzi ...
between the ''input'' and the ''output''. This principle states that ''input'' and ''output'' are distinct, that the system has observable (and relatable) inputs and outputs and that the system is black to the observer (non-openable).Glanville, Ranulph; "Black Boxes", Cybernetics and Human Knowing, 2009, pp. 153-167.


Recording of observed states

An observer makes observations over time. All observations of inputs and outputs of a ''black box'' can be written in a table, in which, at each of a sequence of times, the states of the ''box’s'' various parts, input and output, are recorded. Thus, using an example from Ashby, examining a box that has fallen from a
flying saucer A flying saucer (also referred to as "a flying disc") is a descriptive term for a type of flying craft having a disc or saucer-shaped body, commonly used generically to refer to an anomalous flying object. The term was coined in 1947 but has ...
might lead to this protocol: Thus every system, fundamentally, is investigated by the collection of a long protocol, drawn out in time, showing the sequence of input and output states. From this there follows the fundamental deduction that all knowledge obtainable from a Black Box (of given input and output) is such as can be obtained by re-coding the protocol (the ''observation table''); all that, and nothing more. If the observer also controls input, the investigation turns into an
experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs whe ...
(illustration), and hypotheses about
cause and effect Causality (also referred to as causation, or cause and effect) is influence by which one event, process, state, or object (''a'' ''cause'') contributes to the production of another event, process, state, or object (an ''effect'') where the ca ...
can be tested directly. When the experimenter is also motivated to control the box, there is an active feedback in the box/observer relation, promoting what in
control theory Control theory is a field of mathematics that deals with the control system, control of dynamical systems in engineered processes and machines. The objective is to develop a model or algorithm governing the application of system inputs to drive ...
is called a feed forward architecture.


Modeling

The ''modeling process'' is the construction of a predictive
mathematical model A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used in the natural sciences (such as physics, ...
, using existing historic data (observation table).


Testing the black box model

A developed ''black box model'' is a validated model when '' black-box testing'' methodsSee for ex. the British standard BS 7925-2 (Software component testing), or its 2001 work draft,
BCS SIGIST (British Computer Society Specialist Interest Group in Software Testing), "Standard for Software Component Testing", Working Draft 3.4, 27 April 200
webpage
ensures that it is, based solely on
observable In physics, an observable is a physical quantity that can be measured. Examples include position and momentum. In systems governed by classical mechanics, it is a real-valued "function" on the set of all possible system states. In quantum phy ...
elements. With backtesting, out of time data is always used when testing the black box model. Data has to be written down before it is pulled for black box inputs.


Other theories

''Black box theories'' are those theories defined only in terms of their function. The term can be applied in any field where some inquiry is made into the relations between aspects of the appearance of a system (exterior of the black box), with no attempt made to explain why those relations should exist (interior of the black box). In this context,
Newton's theory of gravitation Newton's law of universal gravitation is usually stated as that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distan ...
can be described as a black box theory. Specifically, the inquiry is focused upon a system that has no immediately apparent characteristics and therefore has only factors for consideration held within itself hidden from immediate observation. The observer is assumed ignorant in the first instance as the majority of available
data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...
is held in an inner situation away from facile investigations. The ''black box'' element of the definition is shown as being characterised by a system where observable elements enter a perhaps imaginary box with a set of different outputs emerging which are also observable.


Adoption in humanities

In humanities disciplines such as
philosophy of mind Philosophy of mind is a branch of philosophy that studies the ontology and nature of the mind and its relationship with the body. The mind–body problem is a paradigmatic issue in philosophy of mind, although a number of other issues are add ...
and
behaviorism Behaviorism is a systematic approach to understanding the behavior of humans and animals. It assumes that behavior is either a reflex evoked by the pairing of certain antecedent stimuli in the environment, or a consequence of that individual ...
, one of the uses of black box theory is to describe and understand
psychological Psychology is the scientific study of mind and behavior. Psychology includes the study of conscious and unconscious phenomena, including feelings and thoughts. It is an academic discipline of immense scope, crossing the boundaries bet ...
factors in fields such as marketing when applied to an analysis of
consumer behaviour Consumer behavior is the study of individuals, groups, or organizations and all the activities associated with the purchase, use and disposal of goods and services. Consumer behaviour consists of how the consumer's emotions, attitudes, and p ...
.


Black box theory

''Black Box theory'' is even wider in application than professional studies:


Applications


Computing and mathematics

*In
computer programming Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as anal ...
and
software engineering Software engineering is a systematic engineering approach to software development. A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate computer software. The term '' ...
, '' black box testing'' is used to check that the output of a program is as expected, given certain inputs.Beizer, Boris; ''Black-Box Testing: Techniques for Functional Testing of Software and Systems'', 1995, The term "black box" is used because the actual program being executed is not examined. * In
computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...
in general, a ''black box program'' is one where the user cannot see the inner workings (perhaps because it is a
closed source Proprietary software is software that is deemed within the free and open-source software to be non-free because its creator, publisher, or other rightsholder or rightsholder partner exercises a legal monopoly afforded by modern copyright and inte ...
program) or one which has no side effects and the function of which need not be examined, a routine suitable for re-use. * Also in
computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...
, a black box refers to a piece of equipment provided by a vendor for the purpose of using that vendor's product. It is often the case that the vendor maintains and supports this equipment, and the company receiving the black box typically is hands-off. *In
mathematical model A mathematical model is a description of a system using mathematical concepts and language. The process of developing a mathematical model is termed mathematical modeling. Mathematical models are used in the natural sciences (such as physics, ...
ing, a limiting case.


Science and technology

*In
neural network A neural network is a network or circuit of biological neurons, or, in a modern sense, an artificial neural network, composed of artificial neurons or nodes. Thus, a neural network is either a biological neural network, made up of biological ...
ing or heuristic algorithms (computer terms generally used to describe 'learning' computers or 'AI simulations'), a black box is used to describe the constantly changing section of the program environment which cannot easily be tested by the programmers. This is also called a white box in the context that the program code can be seen, but the code is so complex that it is functionally equivalent to a black box. * In
physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...
, a black box is a system whose internal structure is unknown, or need not be considered for a particular purpose. *In
cryptography Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or '' -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adv ...
to capture the notion of knowledge obtained by an algorithm through the execution of a
cryptographic protocol A security protocol (cryptographic protocol or encryption protocol) is an abstract or concrete protocol that performs a security-related function and applies cryptographic methods, often as sequences of cryptographic primitives. A protocol descri ...
such as a zero-knowledge proof protocol. If the output of an algorithm when interacting with the protocol matches that of a simulator given some inputs, it only needs to know the inputs.


Other applications

*In
philosophy Philosophy (from , ) is the systematized study of general and fundamental questions, such as those about existence, reason, knowledge, values, mind, and language. Such questions are often posed as problems to be studied or resolved. ...
and
psychology Psychology is the science, scientific study of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious mind, unconscious phenomena, including feelings and thoughts. It is an academic discipline of immens ...
, the school of
behaviorism Behaviorism is a systematic approach to understanding the behavior of humans and animals. It assumes that behavior is either a reflex evoked by the pairing of certain antecedent stimuli in the environment, or a consequence of that individual ...
sees the human mind as a black box;"Mind as a Black Box: The Behaviorist Approach", pp. 85-88, in Friedenberg, Jay; and Silverman, Gordon; ''Cognitive Science: An Introduction to the Study of Mind'', Sage Publications, 2006. see '' other theories''.


See also

*
Black box group In computational group theory, a black box group (black-box group) is a group ''G'' whose elements are encoded by bit strings of length ''N'', and group operations are performed by an oracle (the "black box"). These operations include: • taki ...
*
Blackboxing In science studies, the social process of blackboxing is based on the abstract notion of a black box. To cite Bruno Latour, blackboxing is "the way scientific and technical work is made invisible by its own success. When a machine runs efficient ...
*
Flight recorder A flight recorder is an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of aviation accidents and incidents. The device may often be referred to as a "black box", an outdated name which has ...
* Grey box model *
Hysteresis Hysteresis is the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past. Plots of a single component of ...
* ''Open system'': ** in (general) Systems theory ** in Thermodynamics ** in Control theory *
Multi-agent system A multi-agent system (MAS or "self-organized system") is a computerized system composed of multiple interacting intelligent agents.Hu, J.; Bhowmick, P.; Jang, I.; Arvin, F.; Lanzon, A.,A Decentralized Cluster Formation Containment Framework fo ...
*
Prediction A prediction (Latin ''præ-'', "before," and ''dicere'', "to say"), or forecast, is a statement about a future event or data. They are often, but not always, based upon experience or knowledge. There is no universal agreement about the exact ...
/ Retrodiction * Related theories **
Oracle machine In complexity theory and computability theory, an oracle machine is an abstract machine used to study decision problems. It can be visualized as a Turing machine with a black box, called an oracle, which is able to solve certain problems in a ...
**
Pattern recognition Pattern recognition is the automated recognition of patterns and regularities in data. It has applications in statistical data analysis, signal processing, image analysis, information retrieval, bioinformatics, data compression, computer graphics ...
**
Systems theory Systems theory is the interdisciplinary study of systems, i.e. cohesive groups of interrelated, interdependent components that can be natural or human-made. Every system has causal boundaries, is influenced by its context, defined by its structu ...
**
Signal processing Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing '' signals'', such as sound, images, and scientific measurements. Signal processing techniques are used to optimize transmissions, ...
*
System identification The field of system identification uses statistical methods to build mathematical models of dynamical systems from measured data. System identification also includes the optimal design of experiments for efficiently generating informative dat ...
*
Stimulus–response model The stimulus–response model is a characterization of a statistical unit (such as a neuron). The model allows the prediction of a quantitative response to a quantitative stimulus, for example one administered by a researcher. In psychology, stimul ...


References

{{Authority control Cybernetics Systems theory Metatheory of science Systems science Metaphors referring to objects Software design patterns Programming principles vi:Hộp đen