EVA principle

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The EVA principle describes a basic principle of data processing . The abbreviation is derived from the first letters of the terms input , processing and output ( English IPO model: input-process-output ). These three terms describe the order in which data is processed. The principle is to be seen from the point of view of the processing unit (that can also be a person) and is therefore independent of electronic machines. It is therefore generally applicable to the process of processing data.

EVA principle illustrated

The EVA principle in the IT sector can be described as follows: ( input - processing by data processing system (DVA) - output ). It is considered the basic scheme of data processing . Contrary to popular belief, the memory is not part of processing, but has a kind of special position in the EVA principle, it encapsulates itself. This is expressed as the EVA (S) principle . A device based on the pure EVA principle is stateless , it does not have an internal state that could lead to the same input in two processing operations leading to different results. Therefore, the memory content must always be in the same state at the start of processing (eg "empty").

Only the deviation from the pure EVA principle to stateful logic circuits (see Medvedev automat , as well as Moore automat and Mealy automat ) led from the simple calculating machines to the development of today's computers.

Points of view

The EVA principle can be seen both "spatially" (in the broadest sense) and temporally:

  • Spatial: One area of ​​the IT system is intended for data input (e.g. one side of a circuit board; keyboard, mouse; but also "logically spatial": a program library of a program), another area for processing, and the third part for output. This can relate to the organization of the hardware as well as to the software or to the EDP ​​system (hardware and software) as a whole:
    • In the hardware it must be clear which input signals are to be received (keyboard or mouse inputs, network connections, ...), how they are to be processed (e.g. perform a calculation) and in what form the data is to be output (screen output, printer -, network, sound outputs, ...). Opposite developments are z. B. Smartphones where input (touch screen) and output (same screen) do not have an explicit, clear separation.
    • In the software it must be clear which input data a program receives (keystrokes and / or files from a data carrier, ...), what it should do with it (mathematical calculations, calculation of graphic elements, ...) and what should be output in which form (screen output in text or graphics, storage on a data carrier, ...). The opposite principle is here z. B. Object orientation, in which there is no functional separation, but object-related: Both methods for reading in and for processing and outputting an object are object methods, ie not “spatially separated”; second example: fuzzy logic tries to make unambiguous decisions from unclear input signals; Artificial neural networks try to generate defined outputs from inaccurate input data, whereby it is often not possible to specify an exact processing rule - the network should do it "somehow" and learn through training.
  • temporal: first all entries are recorded (after that no further entries are possible), then processing (while no results are available), and finally the results are output. The opposite principle to this is called streaming , in which new inputs are continuously received, the previous ones are processed at the same time, and the previous ones are currently being sent to the output interface.
In principle, every calculating machine that fulfills both the utm and the smn theorem can also calculate every calculable function. Both computers and computer programs can thus be viewed as functions that receive parameters (E), make a calculation (V) with these parameters and output the result of the calculation (A).

See also


  • Sebastian Dworatschek: Introduction to data processing . 5th edition. ISBN 3-11-004280-0 , pp. 48 ff .
  • Franz-Josef Lintermann, Udo Schaefer, Walter Schulte-Göcking, Klaas Gettner: Simple IT systems. Textbook / specialist book . 5, 1st corrected reprint edition. Bildungsverlag EINS, 2008, ISBN 978-3-8237-1140-7 , p. 16 .