Amathematical model fordata types in which a data type is defined by its behavior (semantics) from the point of view of auser of the data, specifically in terms of possible values, possible operations on data of this type, and the behavior of these operations. This contrasts withdata structures, which are concrete representations of data from the point of view of an implementer rather than a user.
One with only asignature and noimplementation body. It is often used to specify that a subclass must provide an implementation of the method. Abstract methods are used to specifyinterfaces in some computer languages.[1]
1. Insoftware engineering andcomputer science, the process of removing physical, spatial, or temporal details[2] orattributes in the study of objects or systems in order to more closely attend to other details of interest;[3] it is also very similar in nature to the process ofgeneralization.
2. The result of this process: anabstractconcept-object created by keeping common features or attributes to various concrete objects or systems of study.[3]
Indatabase management, afunction in which the values of multiple rows are grouped together to form a single value of more significant meaning or measurement, such as a sum, count, or max.[5]
An unambiguous specification of how to solve a class of problems. Algorithms can performcalculation,data processing, andautomated reasoning tasks. They are ubiquitous in computing technologies.
A method or mathematical process for problem-solving and for engineeringalgorithms. The design of algorithms is part of many solution theories ofoperation research, such asdynamic programming anddivide-and-conquer. Techniques for designing and implementing algorithm designs are also called algorithm design patterns,[8] such as the template method pattern and decorator pattern.
A property of analgorithm which relates to the number ofcomputational resources used by the algorithm. An algorithm must beanalyzed to determine its resource usage, and the efficiency of an algorithm can be measured based on usage of different resources. Algorithmic efficiency can be thought of as analogous to engineeringproductivity for a repeating or continuous process.
Acharacter encoding standard for electronic communications. ASCII codes represent text in computers,telecommunications equipment, and other devices. Most modern character-encoding schemes are based on ASCII, although they support many additional characters.
A set ofsubroutine definitions,communication protocols, and tools for buildingsoftware. In general terms, it is a set of clearly defined methods of communication among various components. A good API makes it easier to develop acomputer program by providing all the building blocks, which are then put together by theprogrammer.
Adata structure consisting of a collection ofelements (values orvariables), each identified by at least onearray index orkey. An array is stored such that the position of each element can be computed from its indextuple by a mathematical formula.[10][11][12] The simplest type of data structure is a linear array, also called a one-dimensional array.
One of many kinds of tangible by-products produced during the development ofsoftware. Some artifacts (e.g.use cases,class diagrams, and otherUnified Modeling Language (UML) models, requirements, and design documents) help describe the function, architecture, and design of software. Other artifacts are concerned with the process of development itself—such as project plans, business cases, and risk assessments.
Intelligence demonstrated bymachines, in contrast to the natural intelligence displayed by humans and other animals. Incomputer science, AI research is defined as the study of "intelligent agents": devices capable of perceiving their environment and taking actions that maximize the chance of successfully achieving their goals.[13] Colloquially, the term "artificial intelligence" is applied when a machine mimics "cognitive" functions that humans associate with otherhuman minds, such as "learning" and "problem solving".[14]
Incomputer programming, astatement that apredicate (Boolean-valued function, i.e. a true–falseexpression) is always true at that point in code execution. It can help a programmer read the code, help acompiler compile it, or help the program detect its own defects. For the latter, some programs check assertions by actually evaluating the predicate as they run and if it is not in fact true – an assertion failure – the program considers itself to be broken and typically deliberatelycrashes or throws an assertion failureexception.
An associative array, map, symbol table, or dictionary is anabstract data type composed of acollection of(key, value) pairs, such that each possible key appears at most once in the collection.Operations associated with this data type allow:[15][16]
the addition of a pair to the collection
the removal of a pair from the collection
the modification of an existing pair
the lookup of a value associated with a particular key
The maximum rate of data transfer across a given path. Bandwidth may be characterized asnetwork bandwidth,[17]data bandwidth,[18] ordigital bandwidth.[19][20]
A formalism and a methodology for having a technique to specifyprobabilistic models and solve problems when less than the necessary information is available.
The act of running acomputer program, a set of programs, or other operations, in order to assess the relative performance of an object, normally by running a number of standard tests and trials against it.[21] The termbenchmark is also commonly utilized for the purposes of elaborately designed benchmarking programs themselves.
Expressions of what theresource usage isat least,at most, andon average, respectively, for a givenalgorithm. Usually the resource being considered is running time, i.e.time complexity, but it could also be memory or some other resource.Best case is the function which performs the minimum number of steps on input data ofn elements;worst case is the function which performs the maximum number of steps on input data of sizen;average case is the function which performs an average number of steps on input data ofn elements.
A mathematical notation that describes thelimiting behavior of afunction when the argument tends towards a particular value or infinity. It is a member of a family of notations invented byPaul Bachmann,[23]Edmund Landau,[24] and others, collectively calledBachmann–Landau notation orasymptotic notation.
In mathematics anddigital electronics, a number expressed in the base-2 numeral system or binary numeral system, which uses only two symbols: typically0 (zero) and1 (one).
Atreedata structure in which each node has at most twochildren, which are referred to as theleft child and theright child. Arecursive definition using justset theory notions is that a (non-empty) binary tree is atuple (L,S,R), whereL andR are binary trees or theempty set andS is asingleton set.[29] Some authors allow the binary tree to be the empty set as well.[30]
Abasic unit of information used incomputing and digital communications; a portmanteau ofbinary digit. Abinary digit can have one of two possiblevalues, and may be physically represented with a two-state device. These state values are most commonly represented as either a0or1.[31]
Incomputing, a basicaccess control mechanism that allows through all elements (email addresses, users, passwords,URLs,IP addresses,domain names, filehashes, etc.), except those explicitly mentioned in a list of prohibited elements. Those items on the list are denied access. The opposite is awhitelist, which means only items on the list are allowed through whatever gate is being used while all other elements are blocked. Agreylist contains items that are temporarily blocked (or temporarily allowed) until an additional step is performed.
Adata type that has one of two possible values (usually denotedtrue andfalse), intended to represent the twotruth values oflogic andBoolean algebra. It is named afterGeorge Boole, who first defined an algebraic system of logic in the mid-19th century. The Boolean data type is primarily associated withconditional statements, which allow different actions by changingcontrol flow depending on whether a programmer-specified Booleancondition evaluates to true or false.[35] It is a special case of a more generallogical data type (seepropositional logic)—i.e. logic need not always be Boolean.
In mathematics andmathematical logic, the branch ofalgebra in which the values of the variables are thetruth valuestrue andfalse, usually denoted 1 and 0, respectively. Contrary toelementary algebra, where the values of the variables are numbers and the prime operations are addition and multiplication, the main operations of Boolean algebra are theconjunctionand (denoted as ∧), thedisjunctionor (denoted as ∨), and thenegationnot (denoted as ¬).[37] It is thus a formalism for describing logical relations in the same way that elementary algebra describes numeric relations.
The procedures implemented in starting up acomputer orcomputer appliance until it can be used. It can be initiated by hardware such as a button press or by a software command. After the power is switched on, the computer is relatively dumb and can read only part of its storage calledread-only memory. There, a small program is stored calledfirmware. It doespower-on self-tests and, most importantly, allows access to other types of memory like ahard disk andmain memory. The firmware loads biggerprograms into the computer'smain memory and runs it.
Anyexecutable code that is passed as anargument to other code that is expected to "call back" (execute) the argument at a given time. This execution may be immediate, as in asynchronous callback, or it might happen at a later time, as in anasynchronous callback.
The electronic circuitry within acomputer that carries out theinstructions of acomputer program by performing the basic arithmetic, logic, controlling, andinput/output (I/O) operations specified by the instructions. The computer industry has used the term "central processing unit" at least since the early 1960s.[40] Traditionally, the term "CPU" refers to aprocessor, more specifically to its processing unit andcontrol unit (CU), distinguishing these core elements of a computer from external components such asmain memory and I/O circuitry.[41]
Inobject-oriented programming, an extensible program-code-template for creatingobjects, providing initial values for state (member variables) and implementations of behavior (member functions ormethods).[43][44] In many languages, the class name is used as the name for the class (the template itself), the name for the defaultconstructor of the class (asubroutine that creates objects), and as thetype of objects generated byinstantiating the class; these distinct concepts are easily conflated.[44]
A piece ofcomputer hardware orsoftware that accesses a service made available by aserver. The server is often (but not always) on anothercomputer system, in which case the client accesses the service by way of anetwork.[45] The term applies to the role that programs or devices play in theclient–server model.
Asoftware development process intended to produce software with a certifiable level ofreliability. The cleanroom process was originally developed byHarlan Mills and several of his colleagues including Alan Hevner atIBM.[46] The focus of the cleanroom process is on defect prevention, rather than defect removal.
Shared pools of configurable computersystem resources and higher-level services that can be rapidlyprovisioned with minimal management effort, often over theInternet. Cloud computing relies on sharing of resources to achieve coherence andeconomies of scale, similar to apublic utility.
Computer programming is the process of designing and building anexecutablecomputer program for accomplishing a specificcomputing task. Programming involves tasks such as analysis, generatingalgorithms, profiling algorithms' accuracy and resource consumption, and the implementation of algorithms in a chosenprogramming language (commonly referred to ascoding[48][49]). Thesource code of a program is written in one or more programming languages. The purpose of programming is to find a sequence of instructions that will automate the performance of a task for solving a given problem. The process of programming thus often requires expertise in several different subjects, including knowledge of theapplication domain, specialized algorithms, and formallogic.
The interdisciplinary,scientific study of themind and its processes.[50] It examines the nature, the tasks, and the functions ofcognition (in a broad sense). Cognitive scientists study intelligence and behavior, with a focus on how nervous systems represent, process, and transforminformation. Mental faculties of concern to cognitive scientists include language, perception, memory, attention, reasoning, and emotion; to understand these faculties, cognitive scientists borrow from fields such as linguistics, psychology,artificial intelligence,philosophy,neuroscience, and anthropology.[51]
A collection or container is a grouping of some variable number of data items (possibly zero) that have some shared significance to the problem being solved and need to be operated upon together in some controlled fashion. Generally, the data items will be of the same type or, in languages supporting inheritance, derived from some common ancestor type. A collection is a concept applicable toabstract data types, and does not prescribe a specific implementation as a concretedata structure, though often there is a conventional choice (seeContainer fortype theory discussion).
A delimitedtext file that uses a comma to separate values. A CSV file storestabular data (numbers and text) inplain text. Each line of the file is a datarecord. Each record consists of one or morefields, separated bycommas. The use of the comma as a field separator is the source of the name for thisfile format.
Any type of calculation[53][54] that includes both arithmetical and non-arithmetical steps and follows a well-definedmodel, e.g. analgorithm. The study of computation is paramount to the discipline ofcomputer science.
A subfield ofcomputational science which focuses on classifying computational problems according to their inherent difficulty, and relating these classes to each other. A computational problem is a task solved by a computer. A computation problem is solvable by mechanical application of mathematical steps, such as analgorithm.
An interdisciplinary field that uses advanced computing capabilities to understand and solve complex problems. It is an area of science which spans many disciplines, but at its core it involves the development of computer models and simulations to understand complex natural systems.
A device that can be instructed to carry out sequences of arithmetic orlogical operations automatically viacomputer programming. Modern computers have the ability to follow generalized sets of operations, calledprograms. These programs enable computers to perform an extremely wide range of tasks.
A set of rules and methods that describe the functionality, organization, and implementation ofcomputer systems. Some definitions of architecture define it as describing the capabilities and programming model of a computer but not a particular implementation.[63] In other definitions computer architecture involvesinstruction set architecture design,microarchitecture design,logic design, andimplementation.[64]
A technology consisting ofcomputer components andrecording media that are used to retain digitaldata. Data storage is a core function and fundamental component of all modern computer systems.[65]: 15–16
Pictures and films created using computers. Usually, the term refers to computer-generated image data created with the help of specialized graphical hardware and software. It is a vast and recently developed area of computer science.
The process of designing and building anexecutablecomputer program for accomplishing a specificcomputing task. Programming involves tasks such as analysis, generatingalgorithms, profiling algorithms' accuracy and resource consumption, and the implementation of algorithms in a chosenprogramming language (commonly referred to ascoding[48][49]). Thesource code of a program is written in one or more programming languages. The purpose of programming is to find a sequence of instructions that will automate the performance of a task for solving a given problem. The process of programming thus often requires expertise in several different subjects, including knowledge of theapplication domain, specialized algorithms, and formallogic.
The theory, experimentation, and engineering that form the basis for the design and use ofcomputers. It involves the study ofalgorithms that process, store, and communicatedigital information. Acomputer scientist specializes in the theory ofcomputation and the design of computational systems.[68]
A person who has acquired the knowledge ofcomputer science, the study of the theoretical foundations of information and computation and their application.
An interdisciplinary scientific field that deals with how computers can be made to gain high-level understanding fromdigital images orvideos. From the perspective of engineering, it seeks to automate tasks that thehuman visual system can do.[70][71][72]
The ability of different parts or units of a program, algorithm, or problem to be executed out-of-order or in partial order, without affecting the final outcome. This allows for parallel execution of the concurrent units, which can significantly improve overall speed of the execution in multi-processor and multi-core systems. In more technical terms, concurrency refers to the decomposability property of a program, algorithm, or problem into order-independent or partially-ordered components or units.[75]
A feature of aprogramming language which performs different computations or actions depending on whether a programmer-specifiedBoolean condition evaluates to true or false. Apart from the case ofbranch predication, this is always achieved by selectively altering thecontrol flow based on some condition.
Is aclass, adata structure,[76][77] or anabstract data type (ADT) whose instances are collections of other objects. In other words, they store objects in an organized way that follows specific access rules. The size of the container depends on the number of objects (elements) it contains. Underlying (inherited) implementations of various container types may vary in size and complexity, and provide flexibility in choosing the right implementation for any given scenario.
Producing software in short cycles with high speed and frequency so that reliable software can be released at any time, with a simple and repeatable deployment process when deciding to deploy.
Inmultitasking computeroperating systems, a daemon (/ˈdiːmən/ or/ˈdeɪmən/)[84] is acomputer program that runs as abackground process, rather than being under the direct control of an interactive user. Traditionally, the process names of a daemon end with the letterd, for clarification that the process is in fact a daemon, and for differentiation between a daemon and a normal computer program. For example,syslogd is a daemon that implements system logging facility, andsshd is a daemon that serves incomingSSH connections.
A dedicated space used to housecomputer systems and associated components, such as telecommunications anddata storage systems. It generally includesredundant or backup components and infrastructure forpower supply, data communications connections, environmental controls (e.g. air conditioning and fire suppression) and various security devices.[85]
An organized collection ofdata, generally stored and accessed electronically from a computer system. Where databases are more complex, they are often developed using formal design and modeling techniques.
An interdisciplinary field that uses scientific methods, processes, algorithms, and systems to extract knowledge and insights fromdata in various forms, both structured and unstructured,[91][92] similar todata mining. Data science is a "concept to unify statistics, data analysis, machine learning and their related methods" in order to "understand and analyze actual phenomena" with data.[93] It employs techniques and theories drawn from many fields within the context of mathematics, statistics,information science, andcomputer science.
A data organization, management, and storage format that enablesefficient access and modification.[94][95][96] More precisely, a data structure is a collection of data values, the relationships among them, and the functions or operations that can be applied to the data.[97]
An attribute ofdata which tells thecompiler orinterpreter how the programmer intends to use the data. Mostprogramming languages support common data types ofreal,integer, andBoolean. A data type constrains the values that anexpression, such as avariable or afunction, might take. This data type defines the operations that can be done on the data, the meaning of the data, and the way values of that type can be stored. A type of value from which an expression may take its value.[98][99]
Incomputer programming, alanguage construct that specifies properties of anidentifier: it declares what a word (identifier) "means".[100] Declarations are most commonly used forfunctions,variables,constants, andclasses, but can also be used for other entities such as enumerations and type definitions.[100] Beyond the name (the identifier itself) and the kind of entity (function, variable, etc.), declarations typically specify thedata type (for variables and constants), or thetype signature (for functions); types may also include dimensions, such as for arrays. A declaration is used to announce the existence of the entity to thecompiler; this is important in thosestrongly typed languages that require functions, variables, and constants, and their types, to be specified with a declaration before use, and is used inforward declaration.[101] The term "declaration" is frequently contrasted with the term "definition",[100] but meaning and usage varies significantly between languages.
A model of the operation of a system as adiscrete sequence of events in time. Each event occurs at a particular instant in time and marks a change ofstate in the system.[102] Between consecutive events, no change in the system is assumed to occur; thus thesimulation can directly jump in time from one event to the next.
(Also sometimes called drive storage) is a general category of storage mechanisms where data is recorded by various electronic, magnetic, optical, or mechanical changes to a surface layer of one or more rotating disks. A disk drive is a device implementing such a storage mechanism. Notable types are thehard disk drive (HDD) containing a non-removable disk, thefloppy disk drive (FDD) and its removablefloppy disk, and variousoptical disc drives (ODD) and associatedoptical disc media.
Analgorithm design paradigm based on multi-branchedrecursion. A divide-and-conqueralgorithm works by recursively breaking down a problem into two or more sub-problems of the same or related type, until these become simple enough to be solved directly. The solutions to the sub-problems are then combined to give a solution to the original problem.
Written text or illustration that accompaniescomputer software or is embedded in thesource code. It either explains how it operates or how to use it, and may mean different things to people in different roles.
Is the targeted subject area of acomputer program. It is a term used insoftware engineering. Formally it represents the target subject of a specific programming project, whether narrowly or broadly defined.[104]
A hierarchical and decentralized naming system for computers, services, or other resources connected to theInternet or to a private network. It associates various information withdomain names assigned to each of the participating entities. Most prominently, it translates more readily memorized domain names to the numericalIP addresses needed for locating and identifying computer services and devices with the underlyingnetwork protocols. By providing a worldwide,distributeddirectory service, the Domain Name System has been an essential component of the functionality of the Internet since 1985.
Incomputer networks, to receive data from a remote system, typically aserver[105] such as aweb server, anFTP server, anemail server, or other similar systems. This contrasts withuploading, where data is sentto a remote server. Adownload is afile offered for downloading or that has been downloaded, or the process of receiving such a file.
A device which provides an entry point into enterprise or service provider core networks. Examples includerouters, routingswitches,integrated access devices (IADs), multiplexers, and a variety ofmetropolitan area network (MAN) andwide area network (WAN) access devices. Edge devices also provide connections into carrier and service provider networks. An edge device that connects alocal area network to a high speed switch or backbone (such as an ATM switch) may be called an edge concentrator.
Incryptography, encryption is the process ofencoding information. This process converts the original representation of the information, known asplaintext, into an alternative form known asciphertext. Ideally, only authorized parties can decipher a ciphertext back to plaintext and access the original information. Encryption does not itself prevent interference but denies the intelligible content to a would-be interceptor. For technical reasons, an encryption scheme usually uses apseudo-random encryptionkey generated by analgorithm. It is possible to decrypt the message without possessing the key, but, for a well-designed encryption scheme, considerable computational resources and skills are required. An authorized recipient can easily decrypt the message with the key provided by the originator to recipients but not to unauthorized users. Historically, various forms of encryption have been used to aid in cryptography. Early encryption techniques were often utilized in military messaging. Since then, new techniques have emerged and become commonplace in all areas of modern computing.[106] Modern encryption schemes utilize the concepts ofpublic-key andsymmetric-key.[106] Modern encryption techniques ensure security because modern computers are inefficient at cracking the encryption.
An action or occurrence recognized by software, often originatingasynchronously from the external environment, that may behandled by the software. Because an event is an entity which encapsulates the action and the contextual variables triggering the action, the acrostic mnemonic "ExecutionVariableEncapsulatingNamedTrigger" is often used to clarify the concept.
Alsoexecutable code,executable file,executable program, or simplyexecutable.
Causes a computer "to perform indicated tasks according to encodedinstructions,"[108] as opposed to adata file that must beparsed by a program to be meaningful. The exact interpretation depends upon the use - while "instructions" is traditionally taken to meanmachine code instructions for a physicalCPU, in some contexts a file containingbytecode orscripting language instructions may also be considered executable.
Incomputer and software engineering is the process by which acomputer orvirtual machine executes the instructions of acomputer program. Each instruction of a program is a description of a particular action which to be carried out in order for a specific problem to be solved; as instructions of a program and therefore the actions they describe are being carried out by an executing machine, specific effects are produced in accordance to thesemantics of the instructions being executed.
A system designed around the concept offault tolerance. In essence, they must be able to continue working to a level of satisfaction in the presence of errors or breakdowns.
An investigation which aims to objectively and rationally uncover the strengths and weaknesses of an existing business or proposed venture, opportunities and threats present in thenatural environment, the resources required to carry through, and ultimately the prospects for success.[109][110] In its simplest terms, the two criteria to judge feasibility are cost required and value to be attained.[111]
Data that has several parts, known as arecord, can be divided into fields.Relational databases arrange data as sets ofdatabase records, so calledrows. Each record consists of several fields; the fields of all records form thecolumns.Examples of fields: name, gender, hair colour.
Acomputer program orsubroutine to process astream, producing another stream. While a single filter can be used individually, they are frequently strung together to form apipeline.
Incomputing, floating-point arithmetic (FP) is arithmetic using formulaic representation ofreal numbers as an approximation to support atrade-off between range and precision. For this reason, floating-point computation is often found in systems which include very small and very large real numbers, which require fast processing times. A number is, in general, represented approximately to a fixed number ofsignificant digits (thesignificand) and scaled using anexponent in some fixed base; the base for the scaling is normally two, ten, or sixteen. A number that can be represented exactly is of the following form:
where significand is aninteger, base is an integer greater than or equal to two, and exponent is also an integer.For example:
Acontrol flowstatement for specifyingiteration, which allows code to beexecuted repeatedly. Various keywords are used to specify this statement: descendants ofALGOL use "for", while descendants ofFortran use "do". There are also other possibilities, e.g.COBOL uses "PERFORM VARYING".
A set of mathematically based techniques for thespecification, development, andverification ofsoftware andhardware systems.[112] The use of formal methods for software and hardware design is motivated by the expectation that, as in other engineering disciplines, performing appropriate mathematical analysis can contribute to the reliability and robustness of a design.[113]
The study ofmathematical models of strategic interaction between rational decision-makers.[116] It has applications in all fields ofsocial science, as well as inlogic andcomputer science. Originally, it addressedzero-sum games, in which each participant's gains or losses are exactly balanced by those of the other participants. Today, game theory applies to a wide range of behavioral relations, and is now anumbrella term for thescience of logical decision making in humans, animals, and computers.
A term used to describe the concept that flawed or nonsenseinput data produces nonsenseoutput or "garbage". It can also refer to the unforgiving nature ofprogramming, in which a poorly written program might produce nonsensical behavior.
A multiple of the unitbyte for digital information. Theprefixgiga means 109 in theInternational System of Units (SI). Therefore, one gigabyte is1000000000bytes. The unit symbol for the gigabyte is GB.
Incomputer programming, a variable with globalscope, meaning that it is visible (hence accessible) throughout the program, unlessshadowed. The set of all global variables is known as theglobal environment orglobal state. In compiled languages, global variables are generallystatic variables, whoseextent (lifetime) is the entire runtime of the program, though in interpreted languages (includingcommand-line interpreters), global variables are generally dynamically allocated when declared, since they are not known ahead of time.
In mathematics, the study ofgraphs, which are mathematical structures used to model pairwise relations between objects. A graph in this context is made up ofvertices (also callednodes orpoints) which are connected byedges (also calledlinks orlines). A distinction is made between undirected graphs, where edges link two vertices symmetrically, and directed graphs, where edges link two vertices asymmetrically.
Computational complexity theory focuses on classifying computational problems according to their inherent difficulty, and relating these classes to each other. A computational problem is a task solved by a computer. A computation problem is solvable by mechanical application of mathematical steps, such as an algorithm.
Anyfunction that can be used to mapdata of arbitrary size to data of a fixed size. The values returned by a hash function are calledhash values,hash codes,digests, or simplyhashes. Hash functions are often used in combination with ahash table, a commondata structure used in computer software for rapid data lookup. Hash functions accelerate table or database lookup by detecting duplicated records in a large file.
A specializedtree-baseddata structure which is essentially an almost complete[117] tree that satisfies theheap property: if P is a parentnode of C, then thekey (thevalue) of P is either greater than or equal to (in amax heap) or less than or equal to (in amin heap) the key of C.[118] The node at the "top" of the heap (with no parents) is called theroot node.
Acomparison-basedsorting algorithm. Heapsort can be thought of as an improvedselection sort: like that algorithm, it divides its input into a sorted and an unsorted region, and it iteratively shrinks the unsorted region by extracting the largest element and moving that to the sorted region. The improvement consists of the use of aheap data structure rather than a linear-time search to find the maximum.[119]
Researches the design and use of computer technology, focused on the interfaces between people (users) and computers. Researchers in the field of HCI both observe the ways in which humans interact with computers and design technologies that let humans interact with computers in novel ways. As a field of research, human–computer interaction is situated at the intersection ofcomputer science,behavioral sciences,design,media studies, andseveral other fields of study.
A method ofsoftware development where the product isdesigned, implemented andtested incrementally (a little more is added each time) until the product is finished. It involves both development and maintenance. The product is defined as finished when it satisfies all of its requirements. This model combines the elements of thewaterfall model with the iterative philosophy ofprototyping.
The communication between an information processing system, such as acomputer, and the outside world, possibly a human or another information processing system.Inputs are the signals or data received by the system and outputs are the signals ordata sent from it. The term can also be used as part of an action; to "perform I/O" is to perform aninput or output operation.
Alsofetch–decode–execute cycle or simplyfetch-execute cycle.
The cycle which thecentral processing unit (CPU) follows fromboot-up until the computer has shut down in order to process instructions. It is composed of three main stages: the fetch stage, the decode stage, and the execute stage.
A datum of integral data type, adata type that represents somerange of mathematicalintegers. Integral data types may be of different sizes and may or may not be allowed to contain negative values. Integers are commonly represented in a computer as a group of binary digits (bits). The size of the grouping varies so the set of integer sizes available varies between different types of computers. Computer hardware, includingvirtual machines, nearly always provide a way to represent a processorregister or memory address as an integer.
(sometimes called integration and testing, abbreviated I&T) is the phase insoftware testing in which individual software modules are combined and tested as a group. Integration testing is conducted to evaluate thecompliance of a system or component with specifiedfunctional requirements.[120] It occurs afterunit testing and beforevalidation testing. Integration testing takes as its inputmodules that have been unit tested, groups them in larger aggregates, applies tests defined in an integrationtest plan to those aggregates, and delivers as its output the integrated system ready forsystem testing.[121]
Inartificial intelligence, anintelligent agent (IA) refers to anautonomous entity which acts, directing its activity towards achieving goals (i.e. it is anagent), upon anenvironment using observation through sensors and consequent actuators (i.e. it is intelligent).[129] Intelligent agents may alsolearn or useknowledge to achieve their goals. They may be very simple orvery complex. A reflex machine, such as athermostat, is considered an example of an intelligent agent.[130]
A shared boundary across which two or more separate components of acomputer system exchange information. The exchange can be betweensoftware,computer hardware,peripheral devices,humans, and combinations of these.[131] Some computer hardware devices, such as atouchscreen, can both send and receive data through the interface, while others such as a mouse or microphone may only provide an interface to send data to a given system.[132]
Computersoftware is said to have Internal Documentation if the notes on how and why various parts of code operate is included within thesource code as comments. It is often combined with meaningfulvariable names with the intention of providing potential future programmers a means of understanding the workings of the code. This contrasts with externaldocumentation, where programmers keep their notes and explanations in a separate document.
The global system of interconnectedcomputer networks that use theInternet protocol suite (TCP/IP) to link devices worldwide. It is anetwork of networks that consists of private, public, academic, business, and government networks of local to global scope, linked by a broad array of electronic, wireless, and optical networking technologies.
Asoftware application that runs automated tasks (scripts) over theInternet.[133] Typically, bots perform tasks that are both simple and structurally repetitive, at a much higher rate than would be possible for a human alone. The largest use of bots is inweb spidering (web crawler), in which an automated script fetches, analyzes and files information from web servers at many times the speed of ahuman.
One can encounter invariants that can be relied upon to be true during the execution of a program, or during some portion of it. It is alogical assertion that is always held to be true during a certain phase of execution. For example, aloop invariant is a condition that is true at the beginning and the end of every execution of a loop.
Is the repetition of a process in order to generate an outcome. The sequence will approach some end point or end value. Each repetition of the process is a single iteration, and the outcome of each iteration is then the starting point of the next iteration. Inmathematics andcomputer science, iteration (along with the related technique ofrecursion) is a standard element ofalgorithms.
The first section of anoperating system to load intomemory. As the center of the operating system, the kernel needs to be small, efficient, and loaded into a protected area in the memory so that it cannot be overwritten. It may be responsible for such essential tasks as disk drive management, file management, memory management, process management, etc.
A method for finding an element within alist. It sequentially checks each element of the list until a match is found or the whole list has been searched.[138]
A linear collection of data elements, whose order is not given by their physical placement in memory. Instead, each elementpoints to the next. It is adata structure consisting of a collection ofnodes which together represent asequence.
or link editor, is a computerutility program that takes one or moreobject files generated by acompiler or anassembler and combines them into a singleexecutable file,library file, or another 'object' file. A simpler version that writes its output directly to memory is called theloader, thoughloading is typically considered a separate process.[139]
Anabstract data type that represents a countable number of orderedvalues, where the same value may occur more than once. An instance of a list is a computer representation of the mathematical concept of a finitesequence; the (potentially) infinite analog of a list is astream.[140]: §3.5 Lists are a basic example ofcontainers, as they contain other values. If the same value occurs multiple times, each occurrence is considered a distinct item.
The part of anoperating system that is responsible for loadingprograms andlibraries. It is one of the essential stages in the process of starting a program, as it places programs into memory and prepares them for execution. Loading a program involves reading the contents of theexecutable file containing the program instructions into memory, and then carrying out other required preparatory tasks to prepare the executable for running. Once loading is complete, the operating system starts the program by passing control to the loaded program code.
Incomputer programming, abug in a program that causes it to operate incorrectly, but not to terminate abnormally (orcrash). A logic error produces unintended or undesired output or other behaviour, although it may not immediately be recognized as such.
The technology and methods used to provide imaging-based automatic inspection and analysis for such applications as automatic inspection,process control, and robot guidance, usually in industry. Machine vision refers to many technologies, software and hardware products, integrated systems, actions, methods and expertise. Machine vision as asystems engineering discipline can be considered distinct fromcomputer vision, a form ofcomputer science. It attempts to integrate existing technologies in new ways and apply them to solve real world problems. The term is the prevalent one for these functions in industrial automation environments but is also used for these functions in other environments such as security and vehicle guidance.
Computer data storage, often called storage, is a technology consisting ofcomputer components andrecording media that are used to retain digitaldata. It is a core function and fundamental component of computers.[65]: 15–16
Inobject-oriented programming (OOP), aprocedure associated with amessage and anobject. An object consists of data and behavior. The data and behavior comprise an interface, which specifies how the object may be utilized by any of various consumers[149] of the object.
Insoftware engineering, a software development process is the process of dividingsoftware development work into distinct phases to improvedesign,product management, andproject management. It is also known as a software development life cycle (SDLC). The methodology may include the pre-definition of specificdeliverables and artifacts that are created and completed by a project team to develop or maintain an application.[150]
Ahardware device that converts data into a format suitable for atransmission medium so that it can be transmitted from one computer to another (historically along telephone wires). A modemmodulates one or morecarrier wave signals to encodedigital information for transmission anddemodulates signals to decode the transmitted information. The goal is to produce asignal that can be transmitted easily and decoded reliably to reproduce the original digital data. Modems can be used with almost any means of transmitting analog signals fromlight-emitting diodes toradio. A common type of modem is one that turns thedigital data of acomputer into modulatedelectrical signal for transmission overtelephone lines and demodulated by another modem at the receiver side to recover the digital data.
Is a basic unit of adata structure, such as alinked list ortree data structure. Nodes containdata and also may link to other nodes. Links between nodes are often implemented bypointers.
Innumerical analysis, a numerical method is a mathematical tool designed to solve numerical problems. The implementation of a numerical method with an appropriate convergence check in a programming language is called a numerical algorithm.
The product of acompiler.[152] In a general sense object code is a sequence ofstatements or instructions in a computer language,[153] usually amachine code language (i.e.,binary) or an intermediate language such asregister transfer language (RTL). The term indicates that the code is thegoal or result of the compiling process, with some early sources referring to source code as a "subject program."
A technical approach for analyzing and designing an application, system, or business by applyingobject-oriented programming, as well as using visual modeling throughout the software development process to guide stakeholder communication and product quality.
Aprogramming paradigm based on the concept of "objects", which can containdata, in the form offields (often known asattributes orproperties), and code, in the form ofprocedures (often known asmethods). A feature of objects is an object's procedures that can access and often modify the data fields of the object with which they are associated (objects have a notion of "this" or "self"). In OOP, computer programs are designed by making them out of objects that interact with one another.[154][155] OOP languages are diverse, but the most popular ones areclass-based, meaning that objects areinstances ofclasses, which also determine theirtypes.
A flexible,transparentfiber made bydrawingglass (silica) or plastic to a diameter slightly thicker than that of ahuman hair.[158] Optical fibers are used most often as a means to transmit light between the two ends of the fiber and find wide usage infiber-optic communications, where they permit transmission over longer distances and at higherbandwidths (data rates) than electrical cables. Fibers are used instead ofmetal wires because signals travel along them with lessloss; in addition, fibers are immune toelectromagnetic interference, a problem from which metal wires suffer.[159]
Anagile software development technique in which twoprogrammers work together at one workstation. One, thedriver, writescode while the other, theobserver ornavigator,[160]reviews each line of code as it is typed in. The two programmers switch roles frequently.
A type ofcomputation in which many calculations or the execution ofprocesses are carried out simultaneously.[161] Large problems can often be divided into smaller ones, which can then be solved at the same time. There are several different forms of parallel computing:bit-level,instruction-level,data, andtask parallelism.
Incomputer programming, a special kind ofvariable, used in asubroutine to refer to one of the pieces of data provided as input to the subroutine.[b] These pieces of data are the values[162][163][164] of the arguments (often calledactual arguments oractual parameters) with which the subroutine is going to be called/invoked. An ordered list of parameters is usually included in thedefinition of a subroutine, so that, each time the subroutine is called, its arguments for that call are evaluated, and the resulting values can be assigned to the corresponding parameters.
Any auxiliary or ancillary device connected to or integrated within a computer system and used to send information to or retrieve information from the computer. Aninput device sends data or instructions to the computer; anoutput device provides output from the computer to the user; and aninput/output device performs both functions.
Is anobject in manyprogramming languages that stores amemory address. This can be that of another value located incomputer memory, or in some cases, that ofmemory-mappedcomputer hardware. A pointerreferences a location in memory, and obtaining the value stored at that location is known asdereferencing the pointer. As an analogy, a page number in a book's index could be considered a pointer to the corresponding page; dereferencing such a pointer would be done by flipping to the page with the given page number and reading the text found on that page. The actual format and content of a pointer variable is dependent on the underlyingcomputer architecture.
Incomputer programming, a condition orpredicate that must always be true just after the execution of some section of code or after an operation in aformal specification. Postconditions are sometimes tested usingassertions within the code itself. Often, postconditions are simply included in the documentation of the affected section of code.
Incomputer programming, a condition orpredicate that must always be true just prior to the execution of some section ofcode or before an operation in aformal specification. If a precondition is violated, the effect of the section ofcode becomes undefined and thus may or may not carry out its intended work.Security problems can arise due to incorrect preconditions.
(Also known asmain memory,internal memory orprime memory), often referred to simply asmemory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in uniform manner.
Anabstract data type which is like a regularqueue orstack data structure, but where additionally each element has a "priority" associated with it. In a priority queue, an element with high priority is served before an element with low priority. In some implementations, if two elements have the same priority, they are served according to the order in which they were enqueued, while in other implementations, ordering of elements with the same priority is undefined.
Incomputer programming, a subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particulartask should be performed.Subroutines may be defined within programs, or separately inlibraries that can be used by many programs. In different programming languages, a subroutine may be called a routine, subprogram, function,method, or procedure. Technically, these terms all have different definitions. The generic,umbrella term callable unit is sometimes used.[165]
Program lifecycle phases are the stages acomputer program undergoes, from initial creation to deployment andexecution. The phases are edit time, compile time, link time, distribution time, installation time, load time, and run time.
(PLT) is a branch ofcomputer science that deals with the design, implementation, analysis, characterization, and classification ofprogramming languages and of their individualfeatures. It falls within the discipline of computer science, both depending on and affectingmathematics,software engineering,linguistics and evencognitive science. It has become a well-recognized branch of computer science, and an active research area, with results published in numerousjournals dedicated to PLT, as well as in general computer science and engineering publications.
Acollection in which the entities in the collection are kept in order and the principal (or only) operations on the collection are the addition of entities to the rear terminal position, known asenqueue, and removal of entities from the front terminal position, known asdequeue.
Indigital numeral systems, the number of uniquedigits, including the digit zero, used to represent numbers in apositional numeral system. For example, in the decimal/denary system (the most common system in use today) the radix (base number) is ten, because it uses the ten digits from 0 through 9, and all other numbers are uniquely specified by positional combinations of these ten base digits; in thebinary system that is the standard incomputing, the radix is two, because it uses only two digits, 0 and 1, to uniquely specify each number.
Occurs when a thing is defined in terms of itself or of its type. Recursion is used in a variety of disciplines ranging fromlinguistics tologic. The most common application of recursion is inmathematics andcomputer science, where afunction being defined is applied within its own definition. While this apparently defines an infinite number of instances (function values), it is often done in such a way that no infinite loop or infinite chain of references can occur.
Is a value that enables a program to indirectly access a particulardatum, such as avariable's value or arecord, in thecomputer'smemory or in some otherstorage device. The reference is said to refer to the datum, and accessing the datum is calleddereferencing the reference.
A programming technique of storing the number ofreferences,pointers, orhandles to a resource, such as an object, a block of memory, disk space, and others. Ingarbage collection algorithms, reference counts may be used to deallocate objects which are no longer needed.
(rarelynon-regression testing[180]) is re-runningfunctional andnon-functional tests to ensure that previously developed and tested software still performs after a change.[181] If not, that would be called aregression. Changes that may require regression testing includebug fixes, software enhancements,configuration changes, and even substitution ofelectronic components.[182] As regression test suites tend to grow with each found defect, test automation is frequently involved. Sometimes achange impact analysis is performed to determine an appropriate subset of tests (non-regression analysis[183]).
A sub-discipline ofsystems engineering that emphasizes dependability in thelifecycle management of a product. Reliability describes the ability of a system or component to function under stated conditions for a specified period of time.[186] Reliability is closely related toavailability, which is typically described as the ability of a component or system to function at a specified moment or interval of time.
Insystems engineering andsoftware engineering, requirements analysis focuses on the tasks that determine the needs or conditions to meet the new or altered product or project, taking account of the possibly conflictingrequirements of the variousstakeholders,analyzing, documenting, validating and managing software or system requirements.[187]
The difference between the result produced by a givenalgorithm using exact arithmetic and the result produced by the same algorithm using finite-precision, rounded arithmetic.[189] Rounding errors are due to inexactness in the representation of real numbers and the arithmetic operations done with them. This is a form ofquantization error.[190] When using approximationequations or algorithms, especially when using finitely many digits to represent real numbers (which in theory have infinitely many digits), one of the goals ofnumerical analysis is toestimate computation errors.[191] Computation errors, also callednumerical errors, include bothtruncation errors and roundoff errors.[192]
Anetworking device that forwardsdata packets betweencomputer networks. Routers perform the traffic directing functions on theInternet. Data sent through the internet, such as aweb page oremail, is in the form of data packets. A packet is typicallyforwarded from one router to another router through the networks that constitute aninternetwork (e.g. the Internet) until it reaches its destinationnode.[193]
Incomputer networking a routing table, or routing information base (RIB), is adata table stored in arouter or anetwork host that lists the routes to particular network destinations, and in some cases,metrics (distances) associated with those routes. The routing table contains information about thetopology of the network immediately around it.
Aruntime error is detected after or during the execution (running state) of a program, whereas acompile-time error is detected by thecompiler before the program is ever executed.Type checking,register allocation,code generation, and code optimization are typically done at compile time, but may be done at runtime depending on the particular language and compiler. Many other runtime errors exist and are handled differently by differentprogramming languages, such asdivision by zero errors, domain errors,array subscript out of bounds errors,arithmetic underflow errors, several types of underflow andoverflow errors, and many other runtime errors generally considered as software bugs which may or may not be caught and handled by any particular computer language.
Also known asexternal memory orauxiliary storage, differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses itsinput/output channels to access secondary storage and transfer the desired data to primary storage. Secondary storage is non-volatile (retaining data when power is shut off). Modern computer systems typically have two orders of magnitude more secondary storage than primary storage because secondary storage is less expensive.
Is anin-placecomparisonsorting algorithm. It has anO(n2)time complexity, which makes it inefficient on large lists, and generally performs worse than the similarinsertion sort. Selection sort is noted for its simplicity and has performance advantages over more complicated algorithms in certain situations, particularly whereauxiliary memory is limited.
Inprogramming language theory, semantics is the field concerned with the rigorous mathematical study of the meaning ofprogramming languages. It does so by evaluating the meaning ofsyntactically validstrings defined by a specific programming language, showing the computation involved. In such a case that the evaluation would be of syntactically invalid strings, the result would be non-computation. Semantics describes the processes a computer follows when executing a program in that specific language. This can be shown by describing the relationship between the input and output of a program, or an explanation of how the program will be executed on a certainplatform, hence creating amodel of computation.
Inmathematics, a sequence is an enumerated collection of objects in which repetitions are allowed andorder does matter. Like aset, it containsmembers (also calledelements, orterms). The number of elements (possibly infinite) is called thelength of the sequence. Unlike a set, the same elements can appear multiple times at different positions in a sequence, and order does matter. Formally, a sequence can be defined as afunction whose domain is either the set of thenatural numbers (for infinite sequences) or the set of the firstn natural numbers (for a sequence of finite lengthn).The position of an element in a sequence is itsrank orindex; it is the natural number for which the element is the image. The first element has index 0 or 1, depending on the context or a specific convention. When a symbol is used to denote a sequence, thenth element of the sequence is denoted by this symbol withn as subscript; for example, thenth element of theFibonacci sequenceF is generally denotedFn.For example, (M, A, R, Y) is a sequence of letters with the letter 'M' first and 'Y' last. This sequence differs from (A, R, M, Y). Also, the sequence (1, 1, 2, 3, 5, 8), which contains the number 1 at two different positions, is a valid sequence. Sequences can befinite, as in these examples, orinfinite, such as the sequence of allevenpositive integers (2, 4, 6, ...). Incomputing andcomputer science, finite sequences are sometimes calledstrings,words orlists, the different names commonly corresponding to different ways to represent them incomputer memory; infinite sequences are calledstreams. The empty sequence ( ) is included in most notions of sequence, but may be excluded depending on the context.
Inconcurrency control ofdatabases,[194][195]transaction processing (transaction management), and varioustransactional applications (e.g.,transactional memory[196] andsoftware transactional memory), both centralized anddistributed, atransaction schedule isserializable if its outcome (e.g., the resulting database state) is equal to the outcome of its transactions executed serially, i.e. without overlapping in time. Transactions are normally executed concurrently (they overlap), since this is the most efficient way. Serializability is the major correctness criterion for concurrent transactions' executions[citation needed]. It is considered the highest level ofisolation betweentransactions, and plays an essential role inconcurrency control. As such it is supported in all general purpose database systems.Strong strict two-phase locking (SS2PL) is a popular serializability mechanism utilized in most of the database systems (in various variants) since their early days in the 1970s.
Is the process of translatingdata structures orobject state into a format that can be stored (for example, in afile or memorybuffer) or transmitted (for example, across anetwork connection link) and reconstructed later (possibly in a different computer environment).[197] When the resulting series of bits is reread according to the serialization format, it can be used to create a semantically identical clone of the original object. For many complex objects, such as those that make extensive use ofreferences, this process is not straightforward. Serialization of object-orientedobjects does not include any of their associatedmethods with which they were previously linked.This process of serializing an object is also calledmarshalling an object in some situations.[198][199] The opposite operation, extracting a data structure from a series of bytes, isdeserialization, (also calledunserialization orunmarshalling).
(SLA), is a commitment between a service provider and a client. Particular aspects of the service – quality, availability, responsibilities – are agreed between the service provider and the service user.[201] The most common component of an SLA is that the services should be provided to the customer as agreed upon in the contract. As an example,Internet service providers andtelcos will commonly include service level agreements within the terms of their contracts with customers to define the level(s) of service being sold in plain language terms. In this case the SLA will typically have a technical definition inmean time between failures (MTBF),mean time to repair ormean time to recovery (MTTR); identifying which party is responsible for reporting faults or paying fees; responsibility for various data rates;throughput;jitter; or similar measurable details.
Is anabstract data type that can store unique values, without any particularorder. It is a computer implementation of themathematical concept of afinite set. Unlike most othercollection types, rather than retrieving a specific element from a set, one typically tests a value for membership in a set.
singleton
Pertains to an element that appears exactly once. Inobject-oriented programming, asingleton class has exactly one instance. In mathematics, asingleton is a set having exactly one element. In linguistics, ahapax legomenon is a term that appears exactly once in some corpus. In programming, a singleton variable, occurring only once, might be a dummy argument or a mistake that can be detected by alinter. Contrastunique.
Is a computer program that acts for a user or other program in a relationship of agency, which derives from the Latinagere (to do): an agreement to act on one's behalf. Such "action on behalf of" implies theauthority to decide which, if any, action is appropriate.[202][203] Agents are colloquially known asbots, fromrobot. They may be embodied, as when execution is paired with a robot body, or as software such as a chatbotexecuting on a phone (e.g.Siri) or other computing device. Software agents may be autonomous or work together with other agents or people. Software agents interacting with people (e.g.chatbots,human-robot interaction environments) may possess human-like qualities such asnatural language understanding and speech, personality or embody humanoid form (seeAsimo).
Is the process by which anagent creates a specification of asoftware artifact, intended to accomplishgoals, using a set of primitive components and subject toconstraints.[206] Software design may refer to either "all the activity involved in conceptualizing, framing, implementing, commissioning, and ultimately modifying complex systems" or "the activity followingrequirements specification and beforeprogramming, as ... [in] a stylized software engineering process."[207]
Is the process of conceiving, specifying, designing,programming,documenting,testing, andbug fixing involved in creating and maintainingapplications,frameworks, or other software components. Software development is a process of writing andmaintaining thesource code, but in a broader sense, it includes all that is involved between the conception of the desired software through to the final manifestation of the software, sometimes in a planned andstructured process.[208] Therefore, software development may include research, new development, prototyping, modification, reuse, re-engineering, maintenance, or any other activities that result in software products.[209]
Is the activity of creatingprototypes of software applications, i.e., incomplete versions of thesoftware program being developed. It is an activity that can occur insoftware development and is comparable toprototyping as known from other fields, such asmechanical engineering ormanufacturing. A prototype typically simulates only a few aspects of, and may be completely different from, the final product.
(SRS), is a description of asoftware system to bedeveloped. The software requirements specification lays outfunctional andnon-functional requirements, and it may include a set ofuse cases that describe user interactions that the software must provide to the user for perfect interaction.
Is an investigation conducted to provide stakeholders with information about thequality of thesoftware product or service under test.[215] Software testing can also provide an objective, independent view of the software to allow the business to appreciate and understand the risks of software implementation. Test techniques include the process of executing a program or application with the intent of findingsoftware bugs (errors or other defects), and verifying that the software product is fit for use.
Is analgorithm that puts elements of alist in a certainorder. The most frequently used orders arenumerical order andlexicographical order. Efficientsorting is important for optimizing theefficiency of other algorithms (such assearch andmerge algorithms) that require input data to be in sorted lists. Sorting is also often useful forcanonicalizing data and for producing human-readable output. More formally, the output of any sorting algorithm must satisfy two conditions:
The output is in nondecreasing order (each element is no smaller than the previous element according to the desiredtotal order);
The output is apermutation (a reordering, yet retaining all of the original elements) of the input.
Further, the input data is often stored in anarray, which allowsrandom access, rather than a list, which only allowssequential access; though many algorithms can be applied to either type of data after suitable modification.
Incomputing, source code is any collection of code, with or withoutcomments, written using[216] ahuman-readableprogramming language, usually asplain text. The source code of a program is specially designed to facilitate the work of computerprogrammers, who specify the actions to be performed by a computer mostly by writing source code. The source code is often transformed by anassembler orcompiler intobinarymachine code that can be executed by the computer. The machine code might then be stored forexecution at a later time. Alternatively, source code may beinterpreted and thus immediately executed.
push, which adds an element to the collection, and
pop, which removes the most recently added element that was not yet removed.
The order in which elements come off a stack gives rise to its alternative name, LIFO (last in, first out). Additionally, apeek operation may give access to the top without modifying the stack.[217] The name "stack" for this type of structure comes from the analogy to a set of physical items stacked on top of each other. This structure makes it easy to take an item off the top of the stack, while getting to an item deeper in the stack may require taking off multiple other items first.[218]
Ininformation technology and computer science, a system is described as stateful if it is designed to remember preceding events or user interactions;[219] the remembered information is called the state of the system.
Computer data storage is a technology consisting ofcomputer components andrecording media that are used to retain digitaldata. It is a core function and fundamental component of computers.[65]: 15–16
Is asequence ofdata elements made available over time. A stream can be thought of as items on aconveyor belt being processed one at a time rather than in large batches.
Incomputer programming, a string is traditionally asequence ofcharacters, either as aliteral constant or as some kind of variable. The latter may allow its elements to be mutated and the length changed, or it may be fixed (after creation). A string is generally considered as adata type and is often implemented as anarray data structure ofbytes (orwords) that stores a sequence of elements, typically characters, using somecharacter encoding.String may also denote more generalarrays or other sequence (orlist) data types and structures.
A NoSQL (originally referring to "non-SQL" or "non-relational")[221]database provides a mechanism forstorage andretrieval of data that is modeled in means other than the tabular relations used inrelational databases. Such databases have existed since the late 1960s, but the name "NoSQL" was only coined in the early 21st century,[222] triggered by the needs ofWeb 2.0 companies.[223][224] NoSQL databases are increasingly used inbig data andreal-time web applications.[225] NoSQL systems are also sometimes called "Not only SQL" to emphasize that they may supportSQL-like query languages or sit alongside SQL databases inpolyglot-persistent architectures.[226][227]
Incomputer programming, a subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particulartask should be performed.Subroutines may be defined within programs, or separately inlibraries that can be used by many programs. In different programming languages, a subroutine may be called a routine, subprogram, function,method, or procedure. Technically, these terms all have different definitions. The generic,umbrella term callable unit is sometimes used.[165]
Inmathematics andcomputer science,[228] computer algebra, also called symbolic computation or algebraic computation, is a scientific area that refers to the study and development ofalgorithms andsoftware for manipulatingmathematical expressions and othermathematical objects. Although computer algebra could be considered a subfield ofscientific computing, they are generally considered as distinct fields because scientific computing is usually based onnumerical computation with approximatefloating-point numbers, while symbolic computation emphasizesexact computation with expressions containingvariables that have no given value and are manipulated as symbols.
Is an error in thesyntax of a sequence of characters ortokens that is intended to be written incompile-time. A program will not compile until all syntax errors are corrected. Forinterpreted languages, however, a syntax error may be detected duringprogram execution, and an interpreter's error messages might not differentiate syntax errors from errors of other kinds. There is some disagreement as to just what errors are "syntax errors". For example, some would say that the use of an uninitialized variable's value in Java code is a syntax error, but many others would disagree[229][230] and would classify this as a(static) semantic error.
The system console, computer console, root console,operator's console, or simply console is the text entry and display device for system administration messages, particularly those from theBIOS orboot loader, thekernel, from theinit system and from thesystem logger. It is a physical device consisting of a keyboard and a screen, and traditionally is atext terminal, but may also be agraphical terminal. System consoles are generalized tocomputer terminals, which are abstracted respectively byvirtual consoles andterminal emulators. Today communication with system consoles is generally done abstractly, via thestandard streams (stdin,stdout, andstderr), but there may be system-specific interfaces, for example those used by the system kernel.
In engineering, any type ofdocumentation that describes handling, functionality, and architecture of a technical product or a product underdevelopment or use.[231][232][233] The intended recipient for product technical documentation is both the (proficient)end user as well as the administrator/service or maintenance technician. In contrast to a mere "cookbook"manual, technical documentation aims at providing enough information for a user to understand inner and outer dependencies of the product at hand.
In mathematics, logic, and computer science, a type theory is any of a class offormal systems, some of which can serve as alternatives toset theory as afoundation for all mathematics. In type theory, every "term" has a "type" and operations are restricted to terms of a certain type.
A reference to aweb resource that specifies its location on acomputer network and a mechanism for retrieving it. A URL is a specific type ofUniform Resource Identifier (URI),[237][238] although many people use the two terms interchangeably.[239][c] URLs occur most commonly to reference web pages (http), but are also used for file transfer (ftp), email (mailto), database access (JDBC), and many other applications.
unique
An element that is different from other elements. Database records are kept separate usingunique keys. Aset guarantees that all its elements are unique. The existence of a unique element is modeled usinguniqueness quantification. Finding unique elements in a sequence orlist requiresdata deduplication. Contrastsingleton.
Is a person who utilizes acomputer ornetworkservice. Users of computer systems and software products generally lack the technical expertise required to fully understand how they work.[242]Power users use advanced features of programs, though they are not necessarily capable ofcomputer programming andsystem administration.
Software (asoftware agent) that acts on behalf of auser, such as aweb browser that "retrieves, renders and facilitates end user interaction with Web content".[243] An email reader is amail user agent.
The space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine from the human end, whilst the machine simultaneously feeds back information that aids the operators'decision-making process. Examples of this broad concept of user interfaces include the interactive aspects of computeroperating systems, handtools,heavy machinery operator controls, andprocess controls. The design considerations applicable when creating user interfaces are related to or involve such disciplines asergonomics andpsychology.
The design ofuser interfaces for machines andsoftware, such as computers, home appliances, mobile devices, and other electronic devices, with the focus on maximizingusability and theuser experience. The goal of user interface design is to make the user's interaction as simple and efficient as possible, in terms of accomplishing user goals (user-centered design).
Incomputer programming, a variable, or scalar, is a storage location (identified by amemory address) paired with an associated symbolic name (anidentifier), which contains some known or unknown quantity of information referred to as avalue. The variable name is the usual way toreference the stored value, in addition to referring to the variable itself, depending on the context. This separation of name and content allows the name to be used independently of the exact information it represents. The identifier in computersource code can bebound to a value duringrun time, and the value of the variable may therefore change during the course ofprogram execution.[244][245]
Anemulation of a computer system. Virtual machines are based oncomputer architectures and attempt to provide the same functionality as a physical computer. Their implementations may involve specialized hardware, software, or a combination of both.
Asoftware development process that may be considered an extension of thewaterfall model, and is an example of the moregeneral V-model. Instead of moving down in a linear way, the process steps are bent upwards after thecoding phase, to form the typical V shape. The V-Model demonstrates the relationships between each phase of the development life cycle and its associated phase oftesting. The horizontal and vertical axes represent time or project completeness (left-to-right) and level of abstraction (coarsest-grain abstraction uppermost), respectively.[246]
A breakdown of project activities into linearsequential phases, where each phase depends on the deliverables of the previous one and corresponds to a specialisation of tasks. The approach is typical for certain areas ofengineering design. Insoftware development, it tends to be among the less iterative and flexible approaches, as progress flows in largely one direction ("downwards" like awaterfall) through the phases of conception, initiation,analysis,design,construction,testing,deployment andmaintenance.
A family of wireless networking technologies, based on theIEEE 802.11 family of standards, which are commonly used forlocal area networking of devices andInternet access.Wi‑Fi is a trademark of the non-profitWi-Fi Alliance, which restricts the use of the termWi-Fi Certified to products that successfully completeinteroperability certification testing.[247][248][249]
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Poole, Mackworth & Goebel 1998,p. 1, which provides the version that is used in this article. Note that they use the term "computational intelligence" as a synonym for artificial intelligence.
^Blaauw, Gerrit Anne;Brooks, Jr., Frederick Phillips;Buchholz, Werner (1962),"4: Natural Data Units"(PDF), inBuchholz, Werner (ed.),Planning a Computer System – Project Stretch,McGraw-Hill Book Company, Inc. / The Maple Press Company, York, PA., pp. 39–40,LCCN61-10466,archived(PDF) from the original on 2017-04-03, retrieved2017-04-03,[…] Terms used here to describe the structure imposed by the machine design, in addition tobit, are listed below. Byte denotes a group of bits used to encode a character, or the number of bits transmitted in parallel to and from input-output units. A term other thancharacter is used here because a given character may be represented in different applications by more than one code, and different codes may use different numbers of bits (i.e., different byte sizes). In input-output transmission the grouping of bits may be completely arbitrary and have no relation to actual characters. (The term is coined frombite, but respelled to avoid accidental mutation tobit.) Aword consists of the number of data bits transmitted in parallel from or to memory in one memory cycle.Word size is thus defined as a structural property of the memory. (The termcatena was coined for this purpose by the designers of theBullGAMMA 60 [fr] computer.) Block refers to the number of words transmitted to or from an input-output unit in response to a single input-output instruction. Block size is a structural property of an input-output unit; it may have been fixed by the design or left to be varied by the program. […]
^Sussman and Steele. "Scheme: An interpreter for extended lambda calculus". "... a data structure containing a lambda expression, and an environment to be used when that lambda expression is applied to arguments." (Wikisource)
^Cognitive science is an interdisciplinary field of researchers from Linguistics, psychology, neuroscience, philosophy, computer science, and anthropology that seek to understand the mind.How We Learn: Ask the Cognitive Scientist
^"NIH working definition of bioinformatics and computational biology" (PDF). Biomedical Information Science and Technology Initiative. 17 July 2000. Archived from the original (PDF) on 5 September 2012. Retrieved 18 August 2012.
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^Melnik, Roderick, ed. (2015).Mathematical and Computational Modeling: With Applications in Natural and Social Sciences, Engineering, and the Arts. Wiley.ISBN978-1-118-85398-6.
^What is computational neuroscience? Patricia S. Churchland, Christof Koch, Terrence J. Sejnowski. in Computational Neuroscience pp.46-55. Edited by Eric L. Schwartz. 1993. MIT Press"Computational Neuroscience - the MIT Press". Archived fromthe original on 2011-06-04. Retrieved2009-06-11.
^Thijssen, Jos (2007). Computational Physics. Cambridge University Press.ISBN978-0521833462.
^Clements, Alan.Principles of Computer Hardware (Fourth ed.). p. 1.Architecture describes the internal organization of a computer in an abstract way; that is, it defines the capabilities of the computer and its programming model. You can have two computers that have been constructed in different ways with different technologies but with the same architecture.
^Hennessy, John; Patterson, David.Computer Architecture: A Quantitative Approach (Fifth ed.). p. 11.This task has many aspects, including instruction set design, functional organization, logic design, and implementation.
^Dana H. Ballard; Christopher M. Brown (1982). Computer Vision. Prentice Hall.ISBN0-13-165316-4.
^Huang, T. (1996-11-19). Vandoni, Carlo, E, ed. Computer Vision : Evolution And Promise (PDF). 19th CERN School of Computing. Geneva: CERN. pp. 21–25. doi:10.5170/CERN-1996-008.21.ISBN978-9290830955.
^Milan Sonka; Vaclav Hlavac; Roger Boyle (2008). Image Processing, Analysis, and Machine Vision. Thomson.ISBN0-495-08252-X.
^Sussman, Gerald Jay;Steele, Guy L. Jr. (December 1998)."Scheme: A Interpreter for Extended Lambda Calculus"(PDF).Higher-Order and Symbolic Computation.11 (4):405–439.doi:10.1023/A:1010035624696.S2CID18040106. Archived fromthe original(reprint) on May 21, 2006.We believe that this was the first occurrence of the term "continuation-passing style" in the literature. It has turned out to be an important concept in source code analysis and transformation for compilers and other metaprogramming tools. It has also inspired a set of other "styles" of program expression.
^Han, Jaiwei; Kamber, Micheline; Pei, Jian (2011).Data Mining: Concepts and Techniques (3rd ed.). Morgan Kaufmann.ISBN978-0-12-381479-1.
^Fayyad, Usama; Piatetsky-Shapiro, Gregory; Smyth, Padhraic (1996). "From Data Mining to Knowledge Discovery in Databases" (PDF). Retrieved 17 December 2008.
^Shaffer, C. A. (2011).Data Structures & Algorithm Analysis in C++ (3rd ed.). Mineola, NY: Dover. 1.2.ISBN978-0-486-48582-9.
^abc"A declaration specifies the interpretation and attributes of a set of identifiers. Adefinition of an identifier is a declaration for that identifier that:
for an object [variable or constant], causes storage to be reserved for that object;
for a function, includes the function body;
for an enumeration constant, is the (only) declaration of the identifier;
for a typedef name, is the first (or only) declaration of the identifier."
^Mike Banahan."2.5. Declaration of variables". GBdirect. Retrieved2011-06-08.[A] declaration [...] introduces just the name and type of something but allocates no storage[...].
^Stewart Robinson (2004).Simulation – The practice of model development and use. Wiley.
^abCoulouris, George; Jean Dollimore; Tim Kindberg; Gordon Blair (2011).Distributed Systems: Concepts and Design (5th ed.). Boston: Addison-Wesley.ISBN978-0-132-14301-1.
^Justis, R. T. & Kreigsmann, B. (1979). The feasibility study as a tool for venture analysis.Business Journal of Small Business Management 17 (1) 35-42.
^Georgakellos, D. A. & Marcis, A. M. (2009). Application of the semantic learning approach in the feasibility studies preparation training process.Information Systems Management 26 (3) 231–240.
^Young, G. I. M. (1970). Feasibility studies.Appraisal Journal 38 (3) 376-383.
^The definition "without being explicitly programmed" is often attributed toArthur Samuel, who coined the term "machine learning" in 1959, but the phrase is not found verbatim in this publication, and may be aparaphrase that appeared later. Confer "Paraphrasing Arthur Samuel (1959), the question is: How can computers learn to solve problems without being explicitly programmed?" inKoza, John R.; Bennett, Forrest H.; Andre, David; Keane, Martin A. (1996).Automated Design of Both the Topology and Sizing of Analog Electrical Circuits Using Genetic Programming. Artificial Intelligence in Design '96. Springer, Dordrecht. pp. 151–170.doi:10.1007/978-94-009-0279-4_9.
^Bishop, C. M. (2006), Pattern Recognition and Machine Learning, Springer,ISBN978-0-387-31073-2
^Undergraduate texts include Boolos, Burgess, and Jeffrey(2002),Enderton(2001), and Mendelson(1997). A classic graduate text by Shoenfield(2001) first appeared in 1967.
^Consumers of an object may consist of various kinds of elements, such as other programs, remote computer systems, or computer programmers who wish to utilize the object as part of their own programs.
^abCenters for Medicare & Medicaid Services (CMS) Office of Information Service (2008). Selecting a development approach. Webarticle. United States Department of Health and Human Services (HHS). Re-validated: March 27, 2008. Retrieved 27 Oct 2008.
^Oppel, Andy (2005).SQL Demystified. McGraw Hill. p. 7.ISBN0-07-226224-9.
^"What is a compiler?". TechTarget. Retrieved14 June 2025.Compilers that translate source code to machine code usually target specific OSes and computer architectures. This type of output is sometimes referred to as object code, which is not related to object-oriented programming.
^Kindler, E.; Krivy, I. (2011). "Object-Oriented Simulation of systems with sophisticated control".International Journal of General Systems.40 (3):313–343.doi:10.1080/03081079.2010.539975.S2CID205549734.
^Lewis, John; Loftus, William (2008).Java Software Solutions Foundations of Programming Design 6th ed. Pearson Education Inc.ISBN978-0-321-53205-3., section 1.6 "Object-Oriented Programming"
^Senior, John M.; Jamro, M. Yousif (2009).Optical fiber communications: principles and practice. Pearson Education. pp. 7–9.ISBN978-0130326812.
^Williams, Laurie (February 19–20, 2001).Integrating pair programming into a software development process. 14th Conference on Software Engineering Education and Training. Charlotte. pp. 27–36.doi:10.1109/CSEE.2001.913816.ISBN0-7695-1059-0.One of the programmers, the driver, has control of the keyboard/mouse and actively implements the program. The other programmer, the observer, continuously observes the work of the driver to identify tactical (syntactic, spelling, etc.) defects, and also thinks strategically about the direction of the work.
^Clocksin, William F.; Mellish, Christopher S. (2003).Programming in Prolog. Berlin; New York: Springer-Verlag.ISBN978-3-540-00678-7.
^Bratko, Ivan (2012).Prolog programming for artificial intelligence (4th ed.). Harlow, England; New York: Addison Wesley.ISBN978-0-321-41746-6.
^Covington, Michael A. (1994).Natural language processing for Prolog programmers. Englewood Cliffs, N.J.: Prentice Hall.ISBN978-0-13-629213-5.
^Lloyd, J. W. (1984). Foundations of logic programming. Berlin: Springer-Verlag.ISBN978-3-540-13299-8.
^Kuhlman, Dave. "A Python Book: Beginning Python, Advanced Python, and Python Exercises". Section 1.1. Archived from the original (PDF) on 23 June 2012.
^The National Academies of Sciences, Engineering, and Medicine (2019). Grumbling, Emily; Horowitz, Mark (eds.).Quantum Computing : Progress and Prospects (2018). Washington, D.C.: National Academies Press. p. I-5.doi:10.17226/25196.ISBN978-0-309-47969-1.OCLC1081001288.S2CID125635007.
R Core Team (2016). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URLhttp://www.R-project.org/.
^Vance, Ashlee (2009-01-06)."Data Analysts Captivated by R's Power".The New York Times. Retrieved2018-08-06.R is also the name of a popular programming language used by a growing number of data analysts inside corporations and academia. It is becoming their lingua franca...
^Radványi, Tibor (2014).Database Management Systems. Eszterházy Károly College. p. 19. Archived fromthe original on 23 September 2018. Retrieved23 September 2018.
^Institute of Electrical and Electronics Engineers (1990) IEEE Standard Computer Dictionary: A Compilation of IEEE Standard Computer Glossaries. New York, NYISBN1-55937-079-3
^Maurice Herlihy and J. Eliot B. Moss.Transactional memory: architectural support for lock-free data structures. Proceedings of the 20th annual international symposium on Computer architecture (ISCA '93). Volume 21, Issue 2, May 1993.
^Marshall Cline."C++ FAQ: "What's this "serialization" thing all about?"". Archived fromthe original on 2015-04-05.It lets you take an object or group of objects, put them on a disk or send them through a wire or wireless transport mechanism, then later, perhaps on another computer, reverse the process, resurrecting the original object(s). The basic mechanisms are to flatten object(s) into a one-dimensional stream of bits, and to turn that stream of bits back into the original object(s).
^"1.1.2.2 Clients and Servers".Cisco Networking Academy. Retrieved2025-06-14.Servers are hosts that have software installed that enable them to provide information...Clients are computer hosts that have software installed that enable them to request and display the information obtained from the server.
^Roger S. Pressman Software engineering: a practitioner's approach (eighth edition)
^Ralph, P. and Wand, Y. (2009). A proposal for a formal definition of the design concept. In Lyytinen, K., Loucopoulos, P.,Mylopoulos, J., and Robinson, W., editors, Design Requirements Workshop (LNBIP 14), pp. 103–136. Springer-Verlag, p. 109doi:10.1007/978-3-540-92966-6_6.
^Freeman, Peter; David Hart (2004). "A Science of design for software-intensive systems".Communications of the ACM.47 (8): 19–21 [20].doi:10.1145/1012037.1012054.S2CID14331332.
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^"NOSQL Databases". Archived fromthe original on 2018-12-26.NoSQL DEFINITION: Next Generation Databases mostly addressing some of the points : being non-relational, distributed, open-source and horizontally scalab
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^Knuth, Donald (1997).The Art of Computer Programming. Vol. 1 (3rd ed.). Reading, Massachusetts: Addison-Wesley. pp. 3–4.ISBN0-201-89683-4.
^Kevin Forsberg andHarold Mooz, "The Relationship of System Engineering to the Project Cycle", in Proceedings of the First Annual Symposium of National Council on System Engineering, October 1991: 57–65.
Abran, Alain; Moore, James W.; Bourque, Pierre; Dupuis, Robert; Tripp, Leonard L. (2004).Guide to the Software Engineering Body of Knowledge. IEEE.ISBN978-0-7695-2330-9.
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^In this article, the term "subroutine" refers to any subroutine-like construct, which have different names and slightly different meanings depending on theprogramming language being discussed.
^A URL implies the means to access an indicated resource and is denoted by a protocol or an access mechanism, which is not true of every URI.[240][239] Thushttp://www.example.com is a URL, whilewww.example.com is not.[241]
