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In
software engineering Software engineering is the systematic application of engineering Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The d ...
and
computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of computation, automation, a ...
, abstraction is: * the process of removing physical, spatial, or temporal details or
attributes Attribute may refer to: * Attribute (philosophy), an extrinsic property of an object * Attribute (research), a characteristic of an object * Grammatical modifier, in natural languages * Attribute (computing), a specification that defines a propert ...
in the study of objects or
system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment, is described by its boundaries, structure and purp ...

system
s to focus attention on details of greater importance; it is similar in nature to the process of
generalization A generalization is a form of abstraction Abstraction in its main sense is a conceptual process where general rules and concept Concepts are defined as abstract ideas or general notions that occur in the mind, in speech, or in thought. They ...

generalization
; * the creation of abstract
concept Concepts are defined as abstract ideas A mental representation (or cognitive representation), in 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 bo ...

concept
- objects by mirroring common features or attributes of various non-abstract objects or systems of study – the result of the process of abstraction. , is a fundamental concept in computer science and
software development Software development is the process of conceiving, specifying, designing, programming, documenting, testing, and bug fixing involved in creating and maintaining applications Application may refer to: Mathematics and computing * Application ...
. The process of abstraction can also be referred to as modeling and is closely related to the concepts of ''
theory A theory is a rational Rationality is the quality or state of being rational – that is, being based on or agreeable to reason Reason is the capacity of consciously making sense of things, applying logic Logic (from Ancient Greek, G ...

theory
'' and ''
design A design is a plan or specification for the construction of an object or system or for the implementation of an activity or process, or the result of that plan or specification in the form of a prototype, product or process. The verb ''to design' ...

design
''. can also be considered types of abstractions per their generalization of aspects of
reality Reality is the sum or aggregate of all that is real or existent within a system, as opposed to that which is only imaginary Imaginary may refer to: * Imaginary (sociology), a concept in sociology * The Imaginary (psychoanalysis), a concept by ...

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 or rules of
programming language A programming language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbol (formal), letters are taken from an alphabet (computer science) ...

programming language
s that carry or utilize features of abstraction itself, such as: * the usage of
data type In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Alg ...
s to perform ''data abstraction'' to separate usage from working representations of
data structure In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of ...

data structure
s within programs; * the concept of procedures, functions, or subroutines which represent a specific of implementing
control flow In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algor ...
in programs; * the rules commonly named "abstraction" that generalize
expressions Expression may refer to: Linguistics * Expression (linguistics), a word, phrase, or sentence * Fixed expression, a form of words with a specific meaning * Idiom, a type of fixed expression * Metaphor#Common types, Metaphorical expression, a parti ...
using
free and bound variables In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). ...
in the various versions of
lambda calculus Lambda calculus (also written as ''λ''-calculus) is a formal system in mathematical logic for expressing computability, computation based on function Abstraction (computer science), abstraction and function application, application using variable N ...
; * the usage of
S-expression In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, gener ...
s as an abstraction of data structures and programs in the
Lisp programming language Lisp (historically LISP) is a family of programming language A programming language is a formal language In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathema ...
; * the process of reorganizing common behavior from non-abstract
classes Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
into "abstract classes" using
inheritance Inheritance is the practice of passing on private property Private property is a legal designation for the ownership of property by non-governmental legal entities. Private property is distinguishable from public property Public property i ...
to abstract over sub-classes as seen in the
object-oriented Object-oriented programming (OOP) is a programming paradigm Program, programme, programmer, or programming may refer to: Business and management * Program management, the process of managing several related projects * Time management * P ...
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
and
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...
programming languages.


Rationale

Computing mostly operates independently of the concrete world. The hardware implements a
model of computation A model is an informative representation of an object, person or system. The term originally denoted the plan A plan is typically any diagram or list of steps with details of timing and resources, used to achieve an objective to do something. It ...
that is interchangeable with others. The software is structured in
architecture upright=1.45, alt=Plan d'exécution du second étage de l'hôtel de Brionne (dessin) De Cotte 2503c – Gallica 2011 (adjusted), Plan of the second floor (attic storey) of the Hôtel de Brionne in Paris – 1734. Architecture (Latin ''archi ...
s 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 Greenspun's tenth rule of programming is an aphorism An aphorism (from Greek ἀφορισμός: ''aphorismos'', denoting 'delimitation', 'distinction', and 'definition') is a concise, terse, laconic, or memorable expression of a general truth ...
is an
aphorism An aphorism (from Ancient Greek, Greek ἀφορισμός: ''aphorismos'', denoting 'delimitation', 'distinction', and 'definition') is a concise, terse, laconic, or memorable expression of a general truth or principle. They are often handed do ...
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 languagesA modeling language is any artificial language that can be used to express information or knowledge or systems in a structure that is defined by a consistent set of rules. The rules are used for interpretation of the meaning of components in the stru ...
'' help in planning. ''
Computer languageComputer language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbol (formal), letters are taken from an alphabet (computer science), alphabet ...
s'' can be processed with a computer. An example of this abstraction process is the generational development of
programming language A programming language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbol (formal), letters are taken from an alphabet (computer science) ...

programming language
s from the
machine language In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, ...
to the
assembly language In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, gene ...
and the
high-level language In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algori ...
. Each stage can be used as a stepping stone for the next stage. The language abstraction continues for example in
scripting language A scripting language or script language is a programming language A programming language is a formal language In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathe ...
s and
domain-specific programming languageA domain-specific language (DSL) is a computer languageA computer language is a method of communication with a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. M ...
s. Within a programming language, some features let the programmer create new abstractions. These include
subroutine In computer programming Computer programming is the process of designing and building an executable computer program to accomplish a specific computing result or to perform a particular task. Programming involves tasks such as analysis, generat ...
s,
modules Broadly speaking, modularity is the degree to which a system's components may be separated and recombined, often with the benefit of flexibility and variety in use. The concept of modularity is used primarily to reduce complexity by breaking a syst ...
, polymorphism, and
software component Component-based software engineering (CBSE), also called component-based development (CBD), is a branch of software engineering that emphasizes the separation of concerns In computer science Computer science deals with the theoretical founda ...
s. Some other abstractions such as
software design pattern In software engineering, a software design pattern is a general, reusability, reusable solution to a commonly occurring problem within a given context in software design. It is not a finished design that can be transformed directly into Source code, ...
s and
architectural styles An architectural style is a set of characteristics and features that make a building or other structure notable or historically identifiable. It is a sub-class of Style (visual arts), style in the visual arts generally, and most styles in archite ...
remain invisible to a
translator Translation is the communication of the Meaning (linguistic), meaning of a #Source and target languages, source-language text by means of an Dynamic and formal equivalence, equivalent #Source and target languages, target-language text. The E ...
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 Avram Joel Spolsky (born 1965) is a software engineer and writer. He is the author of ''Joel on Software'', a blog on software development, and the creator of the project management software Trello Trello is a web-based A web application (or ...
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 A foreign function interface (FFI) is a mechanism by which a program written in one programming language A programming language is a formal language In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such t ...
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 language Object-oriented programming (OOP) is a programming paradigm based on the concept of "Object (computer science), objects", which can contain data and code: data in the form of Field (computer science), fields (often known as Attribute (computin ...
s such as
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
,
Object Pascal Object Pascal is an extension to the programming language Pascal Pascal, Pascal's or PASCAL may refer to: People and fictional characters * Pascal (given name), including a list of people with the name * Pascal (surname), including a list of ...
, or
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...
, the concept of abstraction has itself become a declarative statement – using the
syntax In linguistics Linguistics is the scientific study of language, meaning that it is a comprehensive, systematic, objective, and precise study of language. Linguistics encompasses the analysis of every aspect of language, as well as the ...
''function''(''parameters'') = 0; (in
C++ C++ () is a general-purpose programming language In computer software, a general-purpose programming language is a programming language dedicated to a general-purpose, designed to be used for writing software in a wide variety of application ...

C++
) or the keywords ''abstract'' and ''interface'' (in
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...
). After such a declaration, it is the responsibility of the programmer to implement a
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
to instantiate the
object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Entity, something that is tangible and within the grasp of the senses ** Object (abstract), an object which does not exist at any particular time or pl ...
of the declaration. *
Functional programming language In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Alg ...
s commonly exhibit abstractions related to functions, such as lambda abstractions (making a term into a function of some variable) and
higher-order function In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities and t ...
s (parameters are functions). * Modern members of the Lisp programming language family such as
Clojure Clojure (, like ''closure'') is a dynamic programming language, dynamic and functional programming, functional dialect (computing), dialect of the Lisp (programming language), Lisp programming language on the Java (software platform), Java plat ...
, Scheme and
Common Lisp Common Lisp (CL) is a dialect of the Lisp programming language Lisp (historically LISP) is a family of programming language A programming language is a formal language In mathematics Mathematics (from Ancient Greek, Greek: ) incl ...
support macro systems to allow syntactic abstraction. Other programming languages such as Scala also have macros, or very similar
metaprogramming Metaprogramming is a programming technique in which computer program In imperative programming In computer science, imperative programming is a programming paradigm that uses Statement (computer science), statements that change a program's sta ...
features (for example, Haskell has Template Haskell, and
OCaml OCaml ( , formerly Objective Caml) is a general-purpose, multi-paradigm programming language Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. S ...
has MetaOCaml). These can allow a programmer to eliminate
boilerplate code In computer programming, boilerplate code or just boilerplate are sections of code that are repeated in multiple places with little to no variation. When using languages that are considered ''verbose'', the programmer must write a lot of code to ac ...
, abstract away tedious function call sequences, implement new control flow structures, and implement Domain Specific Languages (DSLs), which allow domain-specific concepts to be expressed in concise and elegant ways. All of these, when used correctly, improve both the programmer's efficiency and the clarity of the code by making the intended purpose more explicit. A consequence of syntactic abstraction is also that any Lisp dialect and in fact almost any programming language can, in principle, be implemented in any modern Lisp with significantly reduced (but still non-trivial in some cases) effort when compared to "more traditional" programming languages such as
Python PYTHON was a Cold War contingency plan of the Government of the United Kingdom, British Government for the continuity of government in the event of Nuclear warfare, nuclear war. Background Following the report of the Strath Committee in 1955, the ...
, C or
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...
.


Specification methods

Analysts have developed various methods to formally specify software systems. Some known methods include: * Abstract-model based method (VDM, Z); * Algebraic techniques (Larch, CLEAR, OBJ, ACT ONE, CASL); * Process-based techniques (LOTOS, SDL, Estelle); * Trace-based techniques (SPECIAL, TAM); * Knowledge-based techniques (Refine, Gist).


Specification languages

Specification languages generally rely on abstractions of one kind or another, since specifications are typically defined earlier in a project, (and at a more abstract level) than an eventual implementation. The
UML UML may refer to: * Unified Modeling Language, a software modeling language * University of Massachusetts Lowell, a research university * User-mode Linux, virtual machine software See also

* Unified Medical Language System (UMLS), a medical in ...
specification language, for example, allows the definition of ''abstract'' classes, which in a waterfall project, remain abstract during the architecture and specification phase of the project.


Control abstraction

Programming languages offer control abstraction as one of the main purposes of their use. Computer machines understand operations at the very low level such as moving some bits from one location of the memory to another location and producing the sum of two sequences of bits. Programming languages allow this to be done in the higher level. For example, consider this statement written in a
Pascal Pascal, Pascal's or PASCAL may refer to: People and fictional characters * Pascal (given name), including a list of people with the name * Pascal (surname), including a list of people and fictional characters with the name ** Blaise Pascal, French ...
-like fashion: :a := (1 + 2) * 5 To a human, this seems a fairly simple and obvious calculation (''"one plus two is three, times five is fifteen"''). However, the low-level steps necessary to carry out this evaluation, and return the value "15", and then assign that value to the variable "a", are actually quite subtle and complex. The values need to be converted to binary representation (often a much more complicated task than one would think) and the calculations decomposed (by the compiler or interpreter) into assembly instructions (again, which are much less intuitive to the programmer: operations such as shifting a binary register left, or adding the binary complement of the contents of one register to another, are simply not how humans think about the abstract arithmetical operations of addition or multiplication). Finally, assigning the resulting value of "15" to the variable labeled "a", so that "a" can be used later, involves additional 'behind-the-scenes' steps of looking up a variable's label and the resultant location in physical or virtual memory, storing the binary representation of "15" to that memory location, etc. Without control abstraction, a programmer would need to specify ''all'' the register/binary-level steps each time they simply wanted to add or multiply a couple of numbers and assign the result to a variable. Such duplication of effort has two serious negative consequences: # it forces the programmer to constantly repeat fairly common tasks every time a similar operation is needed # it forces the programmer to program for the particular hardware and instruction set


Structured programming

Structured programming involves the splitting of complex program tasks into smaller pieces with clear flow-control and interfaces between components, with a reduction of the complexity potential for side-effects. In a simple program, this may aim to ensure that loops have single or obvious exit points and (where possible) to have single exit points from functions and procedures. In a larger system, it may involve breaking down complex tasks into many different modules. Consider a system which handles payroll on ships and at shore offices: * The uppermost level may feature a menu of typical end-user operations. * Within that could be standalone executables or libraries for tasks such as signing on and off employees or printing checks. * Within each of those standalone components there could be many different source files, each containing the program code to handle a part of the problem, with only selected interfaces available to other parts of the program. A sign on program could have source files for each data entry screen and the database interface (which may itself be a standalone third party library or a statically linked set of library routines). *Either the database or the payroll application also has to initiate the process of exchanging data with between ship and shore, and that data transfer task will often contain many other components. These layers produce the effect of isolating the implementation details of one component and its assorted internal methods from the others. Object-oriented programming embraces and extends this concept.


Data abstraction

Data abstraction enforces a clear separation between the ''abstract'' properties of a
data type In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Alg ...
and the ''concrete'' details of its implementation. The abstract properties are those that are visible to client code that makes use of the data type—the ''interface'' to the data type—while the concrete implementation is kept entirely private, and indeed can change, for example to incorporate efficiency improvements over time. The idea is that such changes are not supposed to have any impact on client code, since they involve no difference in the abstract behaviour. For example, one could define an
abstract data type In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...
called ''lookup table'' which uniquely associates ''keys'' with ''values'', and in which values may be retrieved by specifying their corresponding keys. Such a lookup table may be implemented in various ways: as a
hash table 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 computer hardware , hardware and ...
, a
binary search tree In computer science, a binary search tree (BST), also called an ordered or sorted binary tree, is a Rooted tree, rooted binary tree whose internal nodes each store a key greater than all the keys in the node's left subtree and less than those i ...

binary search tree
, or even a simple linear
list A ''list'' is any set of items. List or lists may also refer to: People * List (surname)List or Liste is a European surname. Notable people with the surname include: List * Friedrich List (1789–1846), German economist * Garrett List (194 ...
of (key:value) pairs. As far as client code is concerned, the abstract properties of the type are the same in each case. Of course, this all relies on getting the details of the interface right in the first place, since any changes there can have major impacts on client code. As one way to look at this: the interface forms a ''contract'' on agreed behaviour between the data type and client code; anything not spelled out in the contract is subject to change without notice.


Manual data abstraction

While much of data abstraction occurs through computer science and automation, there are times when this process is done manually and without programming intervention. One way this can be understood is through data abstraction within the process of conducting a
systematic review Systematic reviews are a type of Literature review, review that uses repeatable analytical methods to collect secondary data and analyse it. Systematic reviews are a type of evidence synthesis which formulate research questions that are broad or ...
of the literature. In this methodology, data is abstracted by one or several abstractors when conducting a
meta-analysis A meta-analysis is a statistical analysis that combines the results of multiple Randomized controlled trial, scientific studies. Meta-analyses can be performed when there are multiple scientific studies addressing the same question, with each i ...
, with errors reduced through dual data abstraction followed by independent checking, known as
adjudication Adjudication is the legal process by which an arbitration, arbiter or judge reviews evidence (law), evidence and argumentation, including legal reasoning set forth by opposing parties or litigants, to come to a decision which determines rights and ...
.


Abstraction in object oriented programming

In
object-oriented programming Object-oriented programming (OOP) is a programming paradigm Programming paradigms are a way to classify programming languages based on their features. Languages can be classified into multiple paradigms. Some paradigms are concerned mai ...
theory, abstraction involves the facility to define objects that represent abstract "actors" that can perform work, report on and change their state, and "communicate" with other objects in the system. The term
encapsulation Encapsulation may refer to: Chemistry * Molecular encapsulation, in chemistry, the confinement of an individual molecule within a larger molecule * Micro-encapsulation, in material science, the coating of microscopic particles with another materi ...
refers to the hiding of
state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper in Columbia, South Carolina, Un ...
details, but extending the concept of ''data type'' from earlier programming languages to associate ''behavior'' most strongly with the data, and standardizing the way that different data types interact, is the beginning of abstraction. When abstraction proceeds into the operations defined, enabling objects of different types to be substituted, it is called polymorphism. When it proceeds in the opposite direction, inside the types or classes, structuring them to simplify a complex set of relationships, it is called
delegation Schermerhorn, J., Davidson, P., Poole, D., Woods, P., Simon, A., & McBarron, E. (2017). ''Management'' (6th ed., pp. 282–286). Brisbane: John Wiley & Sons Australia. Delegation is one of the core concepts of management Management (or managi ...
or
inheritance Inheritance is the practice of passing on private property Private property is a legal designation for the ownership of property by non-governmental legal entities. Private property is distinguishable from public property Public property i ...
. Various object-oriented programming languages offer similar facilities for abstraction, all to support a general strategy of polymorphism in object-oriented programming, which includes the substitution of one
type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * Type ...
for another in the same or similar role. Although not as generally supported, a
configuration Configuration or configurations may refer to: Computing * Computer configuration or system configuration * Configuration file, a software file used to configure the initial settings for a computer program * Configurator, also known as choice board, ...
or image or package may predetermine a great many of these bindings at
compile-time In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of Algo ...
, link-time, or loadtime. This would leave only a minimum of such bindings to change at run-time.
Common Lisp Object System The Common Lisp Object System (CLOS) is the facility for object-oriented programming Object-oriented programming (OOP) is a programming paradigm Programming paradigms are a way to classify programming languages based on their features. ...
or
Self The self is an individual person as the object of its own reflective consciousness Consciousness, at its simplest, is or of internal and external existence. Despite millennia of analyses, definitions, explanations and debates by philosoph ...
, for example, feature less of a class-instance distinction and more use of delegation for polymorphism. Individual objects and functions are abstracted more flexibly to better fit with a shared functional heritage from
Lisp Lisp (historically LISP) is a family of programming language A programming language is a formal language In logic, mathematics, computer science, and linguistics, a formal language consists of string (computer science), words whose symbo ...
. C++ exemplifies another extreme: it relies heavily on
templates Template may refer to: Tools * Die (manufacturing), used to cut or shape material * Mold, in a molding (process), molding process * Stencil, a pattern or overlay used in graphic arts (drawing, painting, etc.) and sewing to replicate letters, shap ...
and overloading and other static bindings at compile-time, which in turn has certain flexibility problems. Although these examples offer alternate strategies for achieving the same abstraction, they do not fundamentally alter the need to support abstract nouns in code – all programming relies on an ability to abstract verbs as functions, nouns as data structures, and either as processes. Consider for example a sample
Java Java ( id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 147.7 million people, Java is the world's List of ...
fragment to represent some common farm "animals" to a level of abstraction suitable to model simple aspects of their hunger and feeding. It defines an Animal class to represent both the state of the animal and its functions: public class Animal extends LivingThing With the above definition, one could create objects of type and call their methods like this: thePig = new Animal(); theCow = new Animal(); if (thePig.isHungry()) if (theCow.isHungry()) theCow.moveTo(theBarn); In the above example, the class ''Animal'' is an abstraction used in place of an actual animal, ''LivingThing'' is a further abstraction (in this case a generalisation) of ''Animal''. If one requires a more differentiated hierarchy of animals – to differentiate, say, those who provide milk from those who provide nothing except meat at the end of their lives – that is an intermediary level of abstraction, probably DairyAnimal (cows, goats) who would eat foods suitable to giving good milk, and MeatAnimal (pigs, steers) who would eat foods to give the best meat-quality. Such an abstraction could remove the need for the application coder to specify the type of food, so s/he could concentrate instead on the feeding schedule. The two classes could be related using
inheritance Inheritance is the practice of passing on private property Private property is a legal designation for the ownership of property by non-governmental legal entities. Private property is distinguishable from public property Public property i ...
or stand alone, and the programmer could define varying degrees of polymorphism between the two types. These facilities tend to vary drastically between languages, but in general each can achieve anything that is possible with any of the others. A great many operation overloads, data type by data type, can have the same effect at compile-time as any degree of inheritance or other means to achieve polymorphism. The class notation is simply a coder's convenience.


Object-oriented design

Decisions regarding what to abstract and what to keep under the control of the coder become the major concern of object-oriented design and domain analysis—actually determining the relevant relationships in the real world is the concern of object-oriented analysis and design, object-oriented analysis or legacy analysis. In general, to determine appropriate abstraction, one must make many small decisions about scope (domain analysis), determine what other systems one must cooperate with (legacy analysis), then perform a detailed object-oriented analysis which is expressed within project time and budget constraints as an object-oriented design. In our simple example, the domain is the barnyard, the live pigs and cows and their eating habits are the legacy constraints, the detailed analysis is that coders must have the flexibility to feed the animals what is available and thus there is no reason to code the type of food into the class itself, and the design is a single simple Animal class of which pigs and cows are instances with the same functions. A decision to differentiate DairyAnimal would change the detailed analysis but the domain and legacy analysis would be unchanged—thus it is entirely under the control of the programmer, and it is called an abstraction in object-oriented programming as distinct from abstraction in domain or legacy analysis.


Considerations

When discussing formal semantics of programming languages, formal methods or abstract interpretation, abstraction refers to the act of considering a less detailed, but safe, definition of the observed program behaviors. For instance, one may observe only the final result of program executions instead of considering all the intermediate steps of executions. Abstraction is defined to a concrete (more precise) model of execution. Abstraction may be exact or faithful with respect to a property if one can answer a question about the property equally well on the concrete or abstract model. For instance, if one wishes to know what the result of the evaluation of a mathematical expression involving only integers +, -, ×, is worth modular arithmetic, modulo ''n'', then one needs only perform all operations modulo ''n'' (a familiar form of this abstraction is casting out nines). Abstractions, however, though not necessarily exact, should be sound. That is, it should be possible to get sound answers from them—even though the abstraction may simply yield a result of undecidable problem, undecidability. For instance, students in a class may be abstracted by their minimal and maximal ages; if one asks whether a certain person belongs to that class, one may simply compare that person's age with the minimal and maximal ages; if his age lies outside the range, one may safely answer that the person does not belong to the class; if it does not, one may only answer "I don't know". The level of abstraction included in a programming language can influence its overall usability. The Cognitive dimensions framework includes the concept of ''abstraction gradient'' in a formalism. This framework allows the designer of a programming language to study the trade-offs between abstraction and other characteristics of the design, and how changes in abstraction influence the language usability. Abstractions can prove useful when dealing with computer programs, because non-trivial properties of computer programs are essentially undecidable problem, undecidable (see Rice's theorem). As a consequence, automatic methods for deriving information on the behavior of computer programs either have to drop termination (on some occasions, they may fail, crash or never yield out a result), soundness (they may provide false information), or precision (they may answer "I don't know" to some questions). Abstraction is the core concept of abstract interpretation. Model checking generally takes place on abstract versions of the studied systems.


Levels of abstraction

Computer science commonly presents ''levels'' (or, less commonly, ''layers'') of abstraction, wherein each level represents a different model of the same information and processes, but with varying amounts of detail. Each level uses a system of expression involving a unique set of objects and compositions that apply only to a particular domain. Luciano Floridi
''Levellism and the Method of Abstraction''
IEG – Research Report 22.11.04
Each relatively abstract, "higher" level builds on a relatively concrete, "lower" level, which tends to provide an increasingly "granular" representation. For example, gates build on electronic circuits, binary on gates, machine language on binary, programming language on machine language, applications and operating systems on programming languages. Each level is embodied, but not determined, by the level beneath it, making it a language of description that is somewhat self-contained.


Database systems

Since many users of database systems lack in-depth familiarity with computer data-structures, database developers often hide complexity through the following levels: Physical level: The lowest level of abstraction describes ''how'' a system actually stores data. The physical level describes complex low-level data structures in detail. Logical level: The next higher level of abstraction describes ''what'' data the database stores, and what relationships exist among those data. The logical level thus describes an entire database in terms of a small number of relatively simple structures. Although implementation of the simple structures at the logical level may involve complex physical level structures, the user of the logical level does not need to be aware of this complexity. This is referred to as physical data independence. Database administrators, who must decide what information to keep in a database, use the logical level of abstraction. View level: The highest level of abstraction describes only part of the entire database. Even though the logical level uses simpler structures, complexity remains because of the variety of information stored in a large database. Many users of a database system do not need all this information; instead, they need to access only a part of the database. The view level of abstraction exists to simplify their interaction with the system. The system may provide many view (database), views for the same database.


Layered architecture

The ability to provide a
design A design is a plan or specification for the construction of an object or system or for the implementation of an activity or process, or the result of that plan or specification in the form of a prototype, product or process. The verb ''to design' ...

design
of different levels of abstraction can * simplify the design considerably * enable different role players to effectively work at various levels of abstraction * support the portability of software artifacts (model-based ideally) Systems design and Business process modeling, business process design can both use this. Some Software modeling, design processes specifically generate designs that contain various levels of abstraction. Layered architecture partitions the concerns of the application into stacked groups (layers). It is a technique used in designing computer software, hardware, and communications in which system or network components are isolated in layers so that changes can be made in one layer without affecting the others.


See also

* Abstraction principle (computer programming) * Abstraction inversion for an anti-pattern of one danger in abstraction * Abstract data type for an abstract description of a set of data * Algorithm for an abstract description of a computational procedure * Bracket abstraction for making a term into a function of a variable * Data modeling for structuring data independent of the processes that use it * Encapsulation (object-oriented programming), Encapsulation for abstractions that hide implementation details *
Greenspun's Tenth Rule Greenspun's tenth rule of programming is an aphorism An aphorism (from Greek ἀφορισμός: ''aphorismos'', denoting 'delimitation', 'distinction', and 'definition') is a concise, terse, laconic, or memorable expression of a general truth ...
for an aphorism about an (the?) optimum point in the space of abstractions * Higher-order function for abstraction where functions produce or consume other functions * Lambda abstraction for making a term into a function of some variable * List of abstractions (computer science) * Program refinement, Refinement for the opposite of abstraction in computing * Integer (computer science) * Heuristic (computer science)


References

*


Further reading

* *
Abstraction/information hiding
– CS211 course, Cornell University. * * *


External links


SimArch
example of layered architecture for distributed simulation systems. {{DEFAULTSORT:Abstraction (computer science) Data management Articles with example Java code Abstraction Computer science Object-oriented programming