Abstraction (computer science)

In software engineering and computer science, abstraction is:

* The process of removing or generalizing physical, spatial, or temporal details or attributes in the study of objects or systems to focus attention on details of greater importance; it is similar in nature to the process of generalization;
* the creation of abstract concept- objects by mirroring common features or attributes of various non-abstract objects or systems of study – the result of the process of abstraction.

Abstraction, in general, is a fundamental concept in computer science and software development. The process of abstraction can also be referred to as modeling and is closely related to the concepts of ''theory'' and '' design''. Models can also be considered types of abstractions per their generalization of aspects of reality.

Abstraction in computer science is closely related to abstraction in mathematics due to their common focus on building abstractions as objects, but is also related to other notions of abstraction used in other fields such as art.

Abstractions may also refer to real-world objects and systems, rules of computational systems or rules of programming languages that carry or utilize features of abstraction itself, such as:

* the usage of data types to perform ''data abstraction'' to separate usage from working representations of data structures within programs;
* the concept of procedures, functions, or subroutines which represent a specific of implementing control flow in programs;
* the rules commonly named "abstraction" that generalize expressions using free and bound variables in the various versions of lambda calculus;
* the usage of S-expressions as an abstraction of data structures and programs in the Lisp programming language;
* the process of reorganizing common behavior from non-abstract classes into "abstract classes" using inheritance to abstract over sub-classes as seen in the object-oriented C++ and Java programming languages.

Rationale

Computing mostly operates independently of the concrete world. The hardware implements a model of computation that is interchangeable with others. The software is structured in architectures to enable humans to create the enormous systems by concentrating on a few issues at a time. These architectures are made of specific choices of abstractions. Greenspun's Tenth Rule is an aphorism on how such an architecture is both inevitable and complex.

A central form of abstraction in computing is language abstraction: new artificial languages are developed to express specific aspects of a system. '' Modeling languages'' help in planning. ''Computer languages'' can be processed with a computer. An example of this abstraction process is the generational development of programming languages from the machine language to the assembly language and the high-level language. Each stage can be used as a stepping stone for the next stage. The language abstraction continues for example in scripting languages and domain-specific programming languages.

Within a programming language, some features let the programmer create new abstractions. These include subroutines, modules, polymorphism, and software components. Some other abstractions such as software design patterns and architectural styles remain invisible to a translator and operate only in the design of a system.

Some abstractions try to limit the range of concepts a programmer needs to be aware of, by completely hiding the abstractions that they in turn are built on. The software engineer and writer Joel Spolsky has criticised these efforts by claiming that all abstractions are ''leaky'' – that they can never completely hide the details below; however, this does not negate the usefulness of abstraction.

Some abstractions are designed to inter-operate with other abstractions – for example, a programming language may contain a foreign function interface for making calls to the lower-level language.

Abstraction features

Programming languages

Different programming languages provide different types of abstraction, depending on the intended applications for the language. For example:

* In object-oriented programming languages such as C++, Object Pascal, or Java, the concept of abstraction has itself become a declarative statement – using the syntax ''function''(''parameters'') = 0; (in C++) or the keywords ''abstract'' and ''interface'' (in Java). After such a declaration, it is the responsibility of the programmer to implement a class to instantiate the object of the declaration.
* Functional programming languages commonly exhibit abstractions related to functions, such as lambda abstractions (making a term into a function of some variable) and higher-order functions (parameters are functions).
* Modern members of the Lisp programming language family such as Clojure, Scheme and Common Lisp support macro systems to allow syntactic abstraction. Other programming languages such as Scala also have macros, or very similar metaprogramming features (for example, Haskell has Template Haskell, and OCaml has MetaOCaml). These can allow a programmer to eliminate