Black box

This article is about black box systems. For other uses,see Black box (disambiguation).In science, computing, and engineering, a black box is a

Scheme of a black box. Only the behavior of the stimu-lus/response will be accounted for, to infer the (unknowned) box.

device, system or object which can be viewed in terms ofits inputs and outputs (or transfer characteristics), withoutany knowledge of its internal workings. Its implementa-tion is opaque (black). Almost anything might be re-ferred to as a black box: a transistor, algorithm, or thehuman brain.The opposite of a black box is a system where the innercomponents or logic are available for inspection, whichis most commonly referred to as a white box (sometimesalso known as a clear box or a glass box).

1 History

The modern term black box seems to have enteredthe English language around 1945. In electronic circuittheory the process of network synthesis from transferfunctions, which led to electronic circuits being regardedas black boxes characterized by their response to sig-nals applied to their ports, can be traced to WilhelmCauer who published his ideas in their most developedform in 1941.[1] Although Cauer did not himself use theterm, others who followed him certainly did describe themethod as black-box analysis.[2] Vitold Belevitch[3] putsthe concept of black-boxes even earlier, attributing theexplicit use of two-port networks as black boxes to FranzBreisig in 1921 and argues that 2-terminal componentswere implicitly treated as black-boxes before that.In cybernetics, a full treatment was given by Ross Ashbyin 1956.[4] A black box was described by Norbert Wienerin 1961 as an unknown system that was to be identiedusing the techniques of system identication.[5] He sawthe rst step in self-organization as being to be able tocopy the output behaviour of a black box.

2 Theory

SYSTEM

SURROUNDINGS

BOUNDARY

INPUTOUTPUT

OPEN

The open system theory have the foundations of the black boxtheory. Both have focus on input and output ows, representingexchanges with its surroundings.

The black box is an abstraction representing a class ofconcrete open systems which can be viewed solely interms of its stimuli inputs and output reactions. Theconstitution and structure of the box are altogether irrel-evant to approach under consideration, which is purelyexternal or phenomenological. In other words, only thebehavior of the system will be accounted for.[6]

The understanding of a black box is based on the ex-planatory principle, the hypothesis of a causal relationbetween the input and the output, and:[7]

input and output being believed to be distinct, having observable (and relatable) inputs and outputs, being black to the observer (non-openable).

2.1 Recording of observed statesAn observer makes observations over time. All observa-tions of inputs and outputs of a black box can be writtenin a table with the form:in which, at each of a sequence of times, the states ofthe boxs various parts, input and output, are recorded.Thus, using the Ashbys example, the box that fell fromthe Flying saucer might lead to the protocol:[4]

Thus every system, fundamentally, is investigated by thecollection of a long protocol, drawn out in time, showing

1

2 3 EXAMPLES

The observed hydrograph is a graphic of the response of awatershed (a blackbox) with its runo (red) to an input of rain-fall (blue).

When observer can also do some stimulus (input), the relationwith the black box is not only a observation, but an experiment.

the sequence of input and output states. From this therefollows the fundamental deduction that all knowledge ob-tainable from a Black Box (of given input and output) issuch as can be obtained by re-coding the protocol (theobservation table); all that, and nothing more.[4]

If the observer also controls input, the investigation turnsinto an experiment (illustration), and hypothesis aboutcause-and-eect can be tested directly.When the experimenter is also motivated to controlthe box, there is an active feedback in the box/observerrelation, promoting what in control theory is a feed for-ward architecture.

2.2 Modeling

The modeling process is the construction of a predictivemathematical model, using existing historic data (obser-vation table).

2.3 Testing black box modelA developed black box model is a validated model whenblack-box testing methods[8] ensures that, based solely onobservable elements.See also Backtesting: inputs for past events (not used inthe modeling eort) are entered into the model to seehow well the output matches the known results.

3 Examples In computer programming and software engineer-ing, black box testing is used to check that the outputof a program is as expected, given certain inputs.[9]The term black box is used because the actual pro-gram being executed is not examined.

In computing in general, a black box program is onewhere the user cannot see its inner workings (per-haps because it is a closed source program) or onewhich has no side eects and the function of whichneed not be examined, a routine suitable for re-use.

Also in computing, a black box refers to a piece ofequipment provided by a vendor, for the purpose ofusing that vendors product. It is often the case thatthe vendor maintains and supports this equipment,and the company receiving the black box typicallyare hands-o.

In neural networking or heuristic algorithms (com-puter terms generally used to describe 'learning'computers or 'AI simulations) a black box is usedto describe the constantly changing section of theprogram environment which cannot easily be testedby the programmers. This is also called a white boxin the context that the program code can be seen, butthe code is so complex that it is functionally equiva-lent to a black box.

In physics, a black box is a system whose internalstructure is unknown, or need not be considered fora particular purpose.

In mathematical modelling, a limiting case.

In philosophy and psychology, the school ofbehaviorism sees the human mind as a black box;see black box theory.[10]

In neorealist international relations theory, thesovereign state is generally considered a black box:states are assumed to be unitary, rational, self-interested actors, and the actual decision-makingprocesses of the state are disregarded as being

3largely irrelevant. Liberal and constructivist theo-rists often criticize neorealism for the black boxmodel, and refer to much of their work on how statesarrive at decisions as breaking open the black box.

In cryptography to capture the notion of knowledgeobtained by an algorithm through the execution ofa cryptographic protocol such as a zero-knowledgeproof protocol. If the output of the algorithm wheninteracting with the protocol can be simulated bya simulator that interacts only the algorithm, thismeans that the algorithm 'cannot know' anythingmore than the input of the simulator. If the simu-lator can only interact with the algorithm in a blackbox way, we speak of a black box simulator.

Black Box theory is, however, even wider in applicationthan these professional studies:

The child who tries to open a door has tomanipulate the handle (the input) so as to pro-duce the desired movement at the latch (theoutput); and he has to learn how to controlthe one by the other without being able to seethe internal mechanism that links them. Inour daily lives we are confronted at every turnwith systems whose internal mechanisms arenot fully open to inspection, and which mustbe treated by the methods appropriate to theBlack Box.

W. Ross Ashby, AN INTRODUCTIONTO CYBERNETICS, 1957

4 Other uses of the term In aviation, the ight recorder is often called a blackbox, especially by the media, although it is usu-ally bright orange to facilitate their being found af-ter a crash. In an airplane or helicopter, the ightrecorder records the conversation of the pilots andalso logs information about controls and sensors.If an accident happens, investigators can use therecordings to assist in the investigation.

In amateur radio the term black box operator is adisparaging or self-deprecating description of some-one who operates factory made radios without hav-ing a good understanding of how they work. Suchoperators do not build their own equipment (an ac-tivity called homebrewing) or repair their ownblack boxes.[11]

5 See also Black box theory

Blackboxing Flight recorder Hysteresis Open system Oracle machine Pattern recognition Prediction / Retrodiction System identication Systems theory

6 References[1] W. Cauer. Theorie der linearen Wechselstromschaltun-

gen, Vol.I. Akad. Verlags-Gesellschaft Becker und Erler,Leipzig, 1941.

[2] E. Cauer, W. Mathis, and R. Pauli, Life and Work ofWilhelm Cauer (1900 1945)", Proceedings of the Four-teenth International Symposium of Mathematical Theoryof Networks and Systems (MTNS2000), p4, Perpignan,June, 2000. Retrieved online 19 September 2008.

[3] Belevitch, V, Summary of the history of circuit theory,Proceedings of the IRE, vol 50, Iss 5, pp848-855, May1962.

[4] Ashby, W. Ross 1956. An introduction to cybernetics.London: Chapman&Hall, chapter 6 The black box, p86117.

[5] Wiener, Norbert 1961. Cybernetics: or the Control andCommunication in the Animal and the Machine. page xi,MIT Press. ISBN 0-262-73009-X

[6] Mario Bunge (1963), A general black-box theory. Phi-losophy of Science. Vol. 30. No. 4, pp. 346-358.jstor/186066

[7] R. Glanville (2009), Black Boxes, Cybernetics and Hu-man Knowing, pp153-167

[8] See ex. the British standard BS 7925-2 (Software compo-nent testing), or its 2001 work draft,BCS SIGIST (British Computer Society Specialist Inter-est Group in Software Testing), Standard for SoftwareComponent Testing, Working Draft 3.4, 27. April 2001.webpage.

[9] Black-Box Testing: Techniques for Functional Testing ofSoftware and Systems, by Boris Beizer, 1995. ISBN 0-471-12094-4

[10] Mind as a Black Box: The Behaviorist Approach, pp 85-88, in Cognitive Science: An Introduction to the Study ofMind, by Jay Friedenberg, Gordon Silverman, Sage Pub-lications, 2006

[11] http://www.g3ngd.talktalk.net/1950.html

4 7 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

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