<programming, operating system> (Or "application", "app") A
	complete, self-contained program that performs a specific
	function directly for the user.  This is in contrast to system
	software such as the {operating system} {kernel}, {server}
	processes and libraries which exists to support application
	programs.

	Editors for various kinds of documents, {spreadsheets}, and
	text formatters are common examples of applications.  Network
	applications include clients such as those for {FTP},
	{electronic mail}, {telnet} and {WWW}.

	The term is used fairly loosely, for instance, some might say
	that a client and server together form a distributed
	application, others might argue that editors and compilers
	were not applications but tools for building applications.

	One distinction between an application program and the
	operating system is that applications always run in "user
	mode" (or "non-privileged mode"), while operating systems and
	related utilities may run in "supervisor mode" (or "privileged
	mode").

	The term may also be used to distinguish programs which
	communicate via a {graphical user interface} from those which
	are executed from the {command line}.

	(1994-11-28)

<mathematics> A function f : A -> B is surjective or onto or a
	surjection if f A = B.  I.e. f can return any value in B.
	This means that its {image} is its {codomain}.

	Only surjections have {right inverses}, f' : B -> A where
	f (f' x) = x since if f were not a surjection there would be
	elements of B for which f' was not defined.

	See also {bijection}, {injection}.

	(1995-05-27)

1. A program which provides some service to other ({client})
	programs.  The connection between client and server is
	normally by means of {message passing}, often over a
	{network}, and uses some {protocol} to encode the client's
	requests and the server's responses.  The server may run
	continuously (as a {daemon}), waiting for requests to arrive
	or it may be invoked by some higher level daemon which
	controls a number of specific servers ({inetd} on {Unix}).

	There are many servers associated with the {Internet}, such as
	those for {HTTP}, {Network File System}, {Network Information
	Service} (NIS), {Domain Name System} (DNS), {FTP}, {news},
	{finger}, {Network Time Protocol}.  On Unix, a long list can
	be found in /etc/services or in the {NIS} database "services".
	See {client-server}.

	2. A computer which provides some service for other computers
	connected to it via a network.  The most common example is a
	{file server} which has a local disk and services requests
	from remote clients to read and write files on that disk,
	often using {Sun}'s {Network File System} (NFS) {protocol} or
	{Novell Netware} on {PCs}.  Another common example is a {web
	server}.

	[{Jargon File}]

	(2003-12-29)

<language, database, standard> /S Q L/ An industry-standard
	language for creating, updating and, querying {relational
	database management systems}.

	SQL was developed by {IBM} in the 1970s for use in {System R}.
	It is the {de facto standard} as well as being an {ISO} and
	{ANSI} {standard}.  It is often embedded in general purpose
	programming languages.

	The first SQL standard, in 1986, provided basic language
	constructs for defining and manipulating {tables} of data; a
	revision in 1989 added language extensions for {referential
	integrity} and generalised {integrity} {constraints}.  Another
	revision in 1992 provided facilities for {schema} manipulation
	and {data administration}, as well as substantial enhancements
	for data definition and data manipulation.

	Development is currently underway to enhance SQL into a
	computationally complete language for the definition and
	management of {persistent}, complex objects.  This includes:
	generalisation and specialisation hierarchies, {multiple
	inheritance}, user defined {data types}, {triggers} and
	{assertions}, support for {knowledge based systems},
	{recursive query expressions}, and additional data
	administration tools.  It also includes the specification of
	{abstract data types} (ADTs), object identifiers, {methods},
	{inheritance}, {polymorphism}, {encapsulation}, and all of the
	other facilities normally associated with object data
	management.

	The emerging {SQL3} standard is expected to be complete in
	1998.

	According to Allen G. Taylor, SQL does _not_ stand for
	"Structured Query Language".  That, like "SEQUEL" (and its
	pronunciation /see'kw*l/), was just another unofficial name
	for a precursor of SQL.  However, the IBM SQL Reference manual
	for DB2 and Craig Mullins's "DB2 Developer's Guide" say SQL
	_does_ stand for "Structured Query Language".

	{SQL Standards (http://www.jcc.com/sql_stnd.html)}.

	{An SQL parser
	(ftp://ftp.ora.com/published/oreilly/nutshell/lexyacc/)} is
	described in "Lex & Yacc", by Levine, Mason & Brown published
	by O'Reilly.

	{The 1995 SQL Reunion: People, Projects, and Politics
	(http://www.mcjones.org/System_R/SQL_Reunion_95/)}.

	["A Guide to the SQL Standard", C.J. Date, A-W 1987].

	["SQL for Dummies", Allen G. Taylor, IDG Books Worldwide].

	(2005-11-17)

<data, data processing, jargon> /day't*/ (Or "raw data")
	Numbers, {characters}, {images}, or other method of recording,
	in a form which can be assessed by a human or (especially)
	input into a {computer}, stored and {processed} there, or
	transmitted on some {digital channel}.  Computers nearly
	always represent data in {binary}.

	Data on its own has no meaning, only when interpreted by some
	kind of {data processing system} does it take on meaning and
	become {information}.

	People or computers can find patterns in data to perceive
	information, and information can be used to enhance
	{knowledge}.  Since knowledge is prerequisite to wisdom, we
	always want more data and information.  But, as modern
	societies verge on {information overload}, we especially need
	better ways to find patterns.

	1234567.89 is data.

	"Your bank balance has jumped 8087% to $1234567.89" is
	information.

	"Nobody owes me that much money" is knowledge.

	"I'd better talk to the bank before I spend it, because of
	what has happened to other people" is wisdom.

	(1999-04-30)

<software> Instructions for a computer in some programming
	language, often {machine language}.  The word "code" is often
	used to distinguish instructions from {data} (e.g. "The code
	is marked 'read-only'") whereas "{software}" is used in
	contrast with "{hardware}" and may consist of more than just
	code.

	(2000-04-08)

1. <networking> A computer connected to a {network}.

	The term {node} includes devices such as routers and printers
	which would not normally be called "hosts".

	2. <communications> A computer to which one connects using a
	{terminal emulator}.

	(1995-02-16)

<messaging> A model of media distribution were the bits of
	content have to be requested by the user, e.g. normal use of
	{HTTP} on the {World-Wide Web}.

	Opposite: "{push media}".

	(1997-04-10)

<jargon> A {marketroid} term for something he wants to sell
	you without bothering you with the often dizzying distinctions
	between {hardware}, {software}, {services}, {applications},
	{file formats}, companies, brand names and {operating
	systems}.

	"{Flash} is a perfect image-streaming solution."  "What is
	it?"  "Um...  about a thousand dollars."

	See also: {technology}.

	(1998-07-07)

1. <hardware> An electrical conductor.  For distances larger
	than a breadbox, a single line may consist of two electrical
	conductors in twisted, parallel, or concentric arrangement
	used to transport one logical signal.

	By extension, a (usually physical) medium such as an {optical
	fibre} which carries a signal.

	(1995-09-29)

1. <database> A value used to identify a {record} in a
	database, derived by applying some fixed function to the
	record.  The key is often simply one of the {fields} (a
	{column} if the database is considered as a table with records
	being rows, see "{key field}").  Alternatively the key may be
	obtained by applying some function, e.g. a {hash function}, to
	one or more of the fields.  The set of keys for all records
	forms an {index}.  Multiple indexes may be built for one
	database depending on how it is to be searched.

	2. <cryptography> A value which must be fed into the
	{algorithm} used to decode an encrypted message in order to
	reproduce the original {plain text}.  Some encryption schemes
	use the same (secret) key to encrypt and decrypt a message,
	but {public key encryption} uses a "private" (secret) key and
	a "public" key which is known by all parties.

	3. <hardware> An electromechanical {keyboard} button.

	(2003-07-04)

<language, World-Wide Web> (CFML) A {tag} based {markup}
	language used to create {ColdFusion} applications by embedding
	ColdFusion commands in {HTML} files.

	(1999-08-01)

1. <application, algorithm> To arrange a collection of items
	in some specified order.  The items - {records} in a file or
	data structures in memory - consist of one or more {fields} or
	members.  One of these fields is designated as the "sort key"
	which means the records will be ordered according to the value
	of that field.  Sometimes a sequence of key fields is
	specified such that if all earlier keys are equal then the
	later keys will be compared.  Within each field some ordering
	is imposed, e.g. ascending or descending numerical, {lexical
	ordering}, or date.

	Sorting is the subject of a great deal of study since it is a
	common operation which can consume a lot of computer time.
	There are many well-known sorting {algorithms} with different
	time and space behaviour and programming {complexity}.

	Examples are {quicksort}, {insertion sort}, {bubble sort},
	{heap sort}, and {tree sort}.  These employ many different
	data structures to store sorted data, such as {arrays},
	{linked lists}, and {binary trees}.

	2. <tool> The {Unix} utility program for sorting lines of
	files.

	{Unix manual page}: sort(1).

	(1997-02-12)

1. <file format> A single file containing one or (usually)
	more separate files plus information to allow them to be
	extracted (separated) by a suitable program.

	Archives are usually created for software distribution or
	{backup}.  {tar} is a common format for {Unix} archives, and
	{arc} or {PKZIP} for {MS-DOS} and {Microsoft Windows}.

	2. <operating system> To transfer files to slower, cheaper
	media (usually {magnetic tape}) to free the {hard disk} space
	they occupied.  This is now normally done for long-term
	storage but in the 1960s, when disk was much more expensive,
	files were often shuffled regularly between disk and tape.

	3. <networking> {archive site}.

	(1996-12-08)

1. <software> {Annual Change Traffic}.

	2. <company> {Ada Core Technologies}.

	(1999-06-24)

<operating system> A character string which tells a program to
	perform a specific action.  Most commands take {arguments}
	which either modify the action performed or supply it with
	input.  Commands may be typed by the user or read from a file
	by a {command interpreter}.  It is also common to refer to
	menu items as commands.

	(1997-06-21)