<programming, library> A collection of {subroutines} and
	{functions} stored in one or more files, usually in compiled
	form, for linking with other programs.  Libraries are one of
	the earliest forms of organised {code reuse}.  They are often
	supplied by the {operating system} or {software development
	environment} developer to be used in many different programs.
	The routines in a library may be general purpose or designed
	for some specific function such as three dimensional animated
	graphics.

	Libraries are linked with the user's program to form a
	complete {executable}.  The linking may be {static linking}
	or, in some systems, {dynamic linking}.

	(1998-11-21)

The consensus, idea, plan, story, or set of rules that is
	currently being used to inform a behaviour.  This usage is a
	generalisation and (deliberate) abuse of the technical
	meaning.  "What's the theory on fixing this TECO loss?"
	"What's the theory on dinner tonight?"  ("Chinatown, I
	guess.")  "What's the current theory on letting lusers on
	during the day?"  "The theory behind this change is to fix the
	following well-known screw...."

	(1994-12-14)

<theory, programming> (Or "data type") A set of values from
	which a {variable}, {constant}, {function}, or other
	{expression} may take its value.  A type is a classification
	of data that tells the {compiler} or {interpreter} how the
	programmer intends to use it.  For example, the process and
	result of adding two variables differs greatly according to
	whether they are integers, floating point numbers, or strings.

	Types supported by most programming languages include
	{integers} (usually limited to some range so they will fit in
	one {word} of storage), {Booleans}, {floating point numbers},
	and characters.  {Strings} are also common, and are
	represented as {lists} of characters in some languages.

	If s and t are types, then so is s -> t, the type of
	{functions} from s to t; that is, give them a term of type s,
	functions of type s -> t will return a term of type t.

	Some types are {primitive} - built-in to the language, with no
	visible internal structure - e.g. Boolean; others are
	composite - constructed from one or more other types (of
	either kind) - e.g. {lists}, {arrays}, {structures}, {unions}.
	{Object-oriented programming} extends this with {classes}
	which encapsulate both the structure of a type and the
	operations that can be performed on it.

	Some languages provide {strong typing}, others allow {implicit
	type conversion} and/or {explicit type conversion}.

	(2003-12-22)

1. <programming> The prototype for an {object} in an
	{object-oriented language}; analogous to a {derived type} in a
	{procedural language}.  A class may also be considered to be a
	set of objects which share a common structure and behaviour.
	The structure of a class is determined by the {class
	variables} which represent the {state} of an object of that
	class and the behaviour is given by a set of {methods}
	associated with the class.

	Classes are related in a {class hierarchy}.  One class may be
	a specialisation (a "{subclass}") of another (one of its
	"{superclasses}") or it may be composed of other classes or it
	may use other classes in a {client-server} relationship.  A
	class may be an {abstract class} or a {concrete class}.

	See also {signature}.

	2. <programming> See {type class}.

	3. <networking> One of three types of {Internet addresses}
	distinguished by their most significant bits.

	3. <language> A language developed by the {Andrew Project}.
	It was one of the first attempts to add {object-oriented}
	features to {C}.

	(1995-05-01)

1. <mathematics> In the theory of functions, the set of
	argument values for which a {function} is defined.

	See {domain theory}.

	2. <networking> A group of computers whose {hostnames} share a
	common suffix, the "domain name".  The last component of this
	is the {top-level domain}.

	See {administrative domain}, {Domain Name System}, {fully
	qualified domain name}.

	3. {Distributed Operating Multi Access Interactive Network}.

	4. <programming> A specific phase of the {software life cycle}
	in which a developer works.  Domains define developers' and
	users' areas of responsibility and the scope of possible
	relationships between products.

	5. The subject or market in which a piece of software is
	designed to work.

	(1997-12-26)

1. <mathematics> A subset of the {product} of two sets, R : A
	x B.  If (a, b) is an element of R then we write a R b,
	meaning a is related to b by R.  A relation may be:
	{reflexive} (a R a), {symmetric} (a R b => b R a),
	{transitive} (a R b & b R c => a R c), {antisymmetric} (a R b
	& b R a => a = b) or {total} (a R b or b R a).

	See {equivalence relation}, {partial ordering}, {pre-order},
	{total ordering}.

	2. <database> A {table} in a {relational database}.

	(1995-02-28)

In hacker parlance, this word has strong connotations of
	"annoying", or "difficult", or both.  Hackers relish a
	challenge, and enjoy wringing all the irony possible out of
	the ancient Chinese curse "May you live in interesting times".

	[{Jargon File}]

In {object-oriented programming} sending a message to an
	{object} (to invoke a {method}) is equivalent to calling a
	{procedure} in traditional programming languages, except that
	the actual code executed may only be selected at run time
	depending on the {class} of the object.  Thus, in response to
	the message "drawSelf", the method code invoked would be
	different if the target object were a circle or a square.

	(1995-02-16)

A message sent to a {newsgroup} or {mailing list} (may also be
	called "a post") or the act of sending it.  Distinguished from
	a "letter" or ordinary {electronic mail} message by the fact
	that it is broadcast rather than point-to-point.  It is not
	clear whether messages sent to a small mailing list are
	postings or e-mail; perhaps the best dividing line is that if
	you don't know the names of all the potential recipients, it
	is a posting.

	[{Jargon File}]

<programming> (Or "remark") Explanatory text embedded in
	program {source} (or less often data) intended to help human
	readers understand it.

	Code completely without comments is often hard to read, but
	too heavily commented code isn't much better, especially if
	the comments are not kept up-to-date with changes to the code.
	Too much commenting may mean that the code is
	over-complicated.  A good rule is to comment everything that
	needs it but write code that doesn't need much of it.

	A particularly irksome form of over-commenting explains
	exactly what each statement does, even when it is obvious to
	any reasonably competant programmer, e.g.

		/* Open the input file */
		infd = open(input_file, O_RDONLY);

	(1998-04-28)

1. <programming> An {address}, from the point of view of a
	programming language.  A pointer may be typed, with its {type}
	indicating the type of data to which it points.

	The terms "pointer" and "reference" are generally
	interchangable although particular programming languages often
	differentiate these two in subtle ways.  For example, {Perl}
	always calls them references, never pointers.  Conversely, in
	C, "pointer" is used, although "a reference" is often used to
	denote the concept that a pointer implements.

	{Anthony Hoare} once said:

	Pointers are like jumps, leading wildly from one part of the
	data structure to another.  Their introduction into high-level
	languages has been a step backward from which we may never
	recover.

	[C.A.R.Hoare "Hints on Programming Language Design", 1973,
	Prentice-Hall collection of essays and papers by Tony Hoare].

	2. <operating system> (Or "mouse pointer") An {icon}, usually
	a small arrow, that moves on the screen in response to
	movement of a {pointing device}, typically a {mouse}.  The
	pointer shows the user which object on the screen will be
	selected etc. when a mouse button is clicked.

	(1999-07-07)

<jargon> (Said of people, computers, {algorithms}, programs)
	(To be) a success at a given task.

	E.g. "{WYSIWYG} is a clear win for small documents".

	"winnitude" is the quality that something which wins has.
	"winning" is often (ab)used as an adjective.

	Synonyms: {cuspy}, {elegant}.  Antonym: {lose}.  Compare
	{lossy}, {lossless}.

	[{Jargon File}]

	(1996-09-08)

<job> (Or "computer programmer", "developer") Someone who
	writes or debugs {computer programs}, for a living or for fun.
	"Analyst/developer" is a common equivalent job title, implying
	the added role of {system analysis}.  The term may be
	qualified according to the type of software - "{application}
	programmer", "{system programmer}", etc.

	(2000-01-24)

<character> (Or "ctrl", "^") One (or a pair) of {modifier
	keys} found on all modern {keyboards}.  If the control key is
	held down while pressing and releasing certain other keys then
	a "{control character}" is generated, e.g. holding control and
	hitting "A" generates control-A ({ASCII} code 1).  The ASCII
	code for the control character is generally 64 less than that
	for the unmodified character.

	The control key does not generate any character on its own but
	most modern keyboards and {operating systems} allow a program
	to tell whether each of the individual keys on the keyboard
	(including modifier keys) is pressed at any time.

	Control characters mostly have some kind of "non-printing"
	effect on the output such as ringing the bell (Control-G) or
	advancing to the next line (Control-J).  Most have alternative
	names suggesting these functions (Bell, Line Feed, etc.).

	See {ASCII character table}.

	(1997-07-10)

<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. <unit> The standard metric prefixes used in the {Systme
	International d'Units} (SI) conventions for scientific
	measurement.

	Here are the SI magnifying prefixes, along with the
	corresponding binary interpretations in common use:

	 prefix abr decimal  binary

	 yocto-     1000^-8
	 zepto-     1000^-7
	 atto-      1000^-6
	 femto-  f  1000^-5
	 pico-   p  1000^-4
	 nano-   n  1000^-3
	 micro-  *  1000^-2          * Abbreviation: Greek mu
	 milli-  m  1000^-1

	 kilo- 	 k  1000^1  1024^1 = 2^10 = 1,024
	 mega- 	 M  1000^2  1024^2 = 2^20 = 1,048,576
	 giga- 	 G  1000^3  1024^3 = 2^30 = 1,073,741,824
	 tera- 	 T  1000^4  1024^4 = 2^40 = 1,099,511,627,776
	 peta- 	    1000^5  1024^5 = 2^50 = 1,125,899,906,842,624
	 exa-  	    1000^6  1024^6 = 2^60 = 1,152,921,504,606,846,976
	 zetta-     1000^7  1024^7 = 2^70 = 1,180,591,620,717,411,303,424
	 yotta-     1000^8  1024^8 = 2^80 = 1,208,925,819,614,629,174,706,176

	"Femto" and "atto" derive not from Greek but from Danish.

	The abbreviated forms of these prefixes are common in
	electronics and physics.

	When used with bytes of storage, these prefixes usually denote
	multiplication by powers of 1024 = 2^10 (K, M, and G are
	common in computing).  Thus "MB" stands for megabytes (2^20
	bytes).  This common practice goes against the edicts of the
	{BIPM} who deprecate the use of these prefixes for powers of
	two.  The formal SI prefix for 1000 is lower case "k"; some,
	including this dictionary, use this strictly, reserving upper
	case "K" for multiplication by 1024 (KB is thus "kilobytes").

	Also, in data transfer rates the prefixes stand for powers of
	ten so, for example, 28.8 kb/s means 28,800 bits per second.

	The unit is often dropped so one may talk of "a 40K salary"
	(40000 dollars) or "2 meg of disk space" (2*2^20 bytes).

	The accepted pronunciation of the initial G of "giga-" is
	hard, /gi'ga/.

	Confusing 1000 and 1024 (or other powers of 2 and 10 close in
	magnitude) - for example, describing a memory in units of 500K
	or 524K instead of 512K - is a sure sign of the {marketroid}.
	For example, 3.5" {microfloppies} are often described as
	storing "1.44 MB".  In fact, this is completely specious.  The
	correct size is 1440 KB = 1440 * 1024 = 1474560 bytes.  Alas,
	this point is probably lost on the world forever.

	In 1993, hacker Morgan Burke proposed, to general approval on
	{Usenet}, the following additional prefixes: groucho (10^-30),
	harpo (10^-27), harpi (10^27), grouchi (10^30).  This would
	leave the prefixes zeppo-, gummo-, and chico- available for
	future expansion.  Sadly, there is little immediate prospect
	that Mr. Burke's eminently sensible proposal will be ratified.

	2. <language> Related to the {prefix notation}.

	(2003-05-06)

<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)

<programming> (CVS) A {cross-platform} {code management
	system} originally based on {RCS}.

	CVS tracks all revisions to a file in an associated file with
	the same name as the original file but with the string ",v"
	(for version) appended to the filename.  These files are
	stored in a (possibly centralised) repository.

	Changes are checked in or "committed" along with a comment
	(which appears in the the "commit log").  CVS has the notions
	of projects, branches, file locking and many others needed to
	provide a full-functioned repository.

	It is commonly accessed over over its own "anonCVS" {protocol}
	for read-only access (many {open source} projects are
	available by anonymous CVS) and over the {SSH} protocol by
	those with commit privileges ("committers").

	CVS has been rewritten several times and does not depend on
	RCS.  However, files are still largely compatible; one can
	easily migrate a project from RCS to CVS by copying the
	history files into a CVS repository.  A sub-project of the
	{OpenBSD} project is building a complete new implementation of
	CVS, to be called OpenCVS.

	{CVS Home (http://www.cvshome.org/)}.  {OpenCVS
	(http://www.opencvs.org/)}.

	(2005-01-17)

1. <database> See {data dictionary}.

	2. <programming> The core of a {CASE} tool, typically a {DBMS}
	where all development documents are stored.

	(1999-04-27)

<programming> (API, or "application programming interface")
	The interface (calling conventions) by which an {application
	program} accesses {operating system} and other services.  An
	API is defined at {source code} level and provides a level of
	{abstraction} between the application and the {kernel} (or
	other privileged utilities) to ensure the {portability} of the
	code.

	An API can also provide an interface between a {high level
	language} and lower level utilities and services which were
	written without consideration for the {calling conventions}
	supported by compiled languages.  In this case, the API's main
	task may be the translation of parameter lists from one format
	to another and the interpretation of {call-by-value} and
	{call-by-reference} arguments in one or both directions.

	(1995-02-15)

1. The art of debugging a blank sheet of paper (or, in these
	days of on-line editing, the art of debugging an empty file).

	2. A pastime similar to banging one's head against a wall, but
	with fewer opportunities for reward.

	3. The most fun you can have with your clothes on (although
	clothes are not mandatory).

	[{Jargon File}]

	(2003-02-12)

<programming> One of a sequence of copies of a program, each
	incorporating new modifications.  Each version is usually
	identified by a number, commonly of the form X.Y where X is
	the major version number and Y is the release number.
	Typically an increment in X (with Y reset to zero) signifies a
	substantial increase in the function of the program or a
	partial or total re-implementation, whereas Y increases each
	time the progam is changed in any way and re-released.

	Version numbers are useful so that the user can know if the
	program has changed ({bugs} have been fixed or new functions
	added) since he obtained his copy and the programmer can tell
	if a bug report relates to the current version.  It is thus
	always important to state the version when reporting bugs.
	Statements about compatibility between different software
	components should always say which versions they apply to.

	See {change management}.

	(1997-12-07)

<programming> (Or "released version", "baseline") A version of
	a piece of software which has been made public (as opposed to
	a version that is in development, or otherwise unreleased).

	A release is either a {major release}, a {revision}, or a
	{bugfix}.

	Pre-release versions may be called {alpha test}, or {beta
	test} versions.

	See {change management}.

	(1996-08-04)

<unit> (b) {binary} digit.

	The unit of information; the amount of information obtained by
	asking a yes-or-no question; a computational quantity that can
	take on one of two values, such as false and true or 0 and 1;
	the smallest unit of storage - sufficient to hold one bit.

	A bit is said to be "set" if its value is true or 1, and
	"reset" or "clear" if its value is false or 0.  One speaks of
	setting and clearing bits.  To {toggle} or "invert" a bit is
	to change it, either from 0 to 1 or from 1 to 0.

	The term "bit" first appeared in print in the computer-science
	sense in 1949, and seems to have been coined by the eminent
	statistician, {John Tukey}.  Tukey records that it evolved
	over a lunch table as a handier alternative to "bigit" or
	"binit".

	See also {flag}, {trit}, {mode bit}, {byte}, {word}.

	[{Jargon File}]

	(2002-01-22)

<jargon> /do'koh/ 1. (In-house jargon at Symbolics) A
	documentation writer.

	See also {devo} and {mango}.

	2. (UK) A short technical document.  A "doco" is often not the
	documentation passed to management.

	Compare {doc}.

	[{Jargon File}]

	(1999-10-08)

1. <chat> {Unix}'s simple {talk} command and {protocol}.
	write has been largely superseded by {talk} and then {irc}.

	An enhancement, {RWP}, has been proposed.

	2. <tool> A simple {text editor} for {Windows}.

	(1998-04-28)