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Concept
Abstraction layer
Résumé
In computing, an abstraction layer or abstraction level is a way of hiding the working details of a subsystem. Examples of software models that use layers of abstraction include the OSI model for network protocols, OpenGL, and other graphics libraries, which allow the separation of concerns to facilitate interoperability and platform independence. Another example is Media Transfer Protocol.
In computer science, an abstraction layer is a generalization of a conceptual model or algorithm, away from any specific implementation. These generalizations arise from broad similarities that are best encapsulated by models that express similarities present in various specific implementations. The simplification provided by a good abstraction layer allows for easy reuse by distilling a useful concept or design pattern so that situations, where it may be accurately applied, can be quickly recognized.
A layer is considered to be on top of another if it depends on it. Every layer can exist without the layers above it, and requires the layers below it to function. Frequently abstraction layers can be composed into a hierarchy of abstraction levels. The OSI model comprises seven abstraction layers. Each layer of the model encapsulates and addresses a different part of the needs of digital communications, thereby reducing the complexity of the associated engineering solutions.
A famous aphorism of David Wheeler is, "All problems in computer science can be solved by another level of indirection." This is often deliberately misquoted with "abstraction" substituted for "indirection." It is also sometimes misattributed to Butler Lampson. Kevlin Henney's corollary to this is, "...except for the problem of too many layers of indirection."
In a computer architecture, a computer system is usually represented as consisting of several abstraction levels such as:
software
programmable logic
hardware
Programmable logic is often considered part of the hardware, while the logical definitions are also sometimes seen as part of a device's software or firmware.
Source officielle
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