<architecture> {Data} transferred from a computer system to
	the outside world via some kind of {output device}.

	Opposite: {input}.

	(1997-04-28)

The structure of strings in some language.  A language's
	syntax is described by a {grammar}.  For example, the syntax
	of a binary number could be expressed as

		binary_number = bit [ binary_number ]

		bit = "0" | "1"

	meaning that a binary number is a bit optionally followed by a
	binary number and a bit is a literal zero or one digit.

	The meaning of the language is given by its {semantics}.

	See also {abstract syntax}, {concrete syntax}.

	(1994-10-31)

<data processing, signal processing> Performing some
	predefined sequence of operations on an input to produce an
	output or change of internal state; activity specifically
	involving the computer's {CPU}.

	The term is often qualified: "{data processing}" treats
	{digital} data, "{signal processing}" treats {analog} data
	(possibly in digital form), "{word processing}" takes in typed
	human language input and produces digital documents, {image
	processing} transforms digital {images}.

	(2003-10-23)

1. <mathematics> (Or "map", "mapping") If D and C are sets
	(the domain and codomain) then a function f from D to C,
	normally written "f : D -> C" is a subset of D x C such that:

	1. For each d in D there exists some c in C such that (d,c) is
	an element of f.  I.e. the function is defined for every
	element of D.

	2. For each d in D, c1 and c2 in C, if both (d,c1) and (d,c2)
	are elements of f then c1 = c2.  I.e. the function is uniquely
	defined for every element of D.

	See also {image}, {inverse}, {partial function}.

	2. <programming> Computing usage derives from the mathematical
	term but is much less strict.  In programming (except in
	{functional programming}), a function may return different
	values each time it is called with the same argument values
	and may have {side effects}.

	A {procedure} is a function which returns no value but has
	only {side-effects}.  The {C} language, for example, has no
	procedures, only functions.  {ANSI C} even defines a {type},
	{void}, for the result of a function that has no result.

	(1996-09-01)

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)

<World-Wide Web, database, tool> {Allaire Corporation}'s
	commercial {database} application development tool that allows
	{databases} to have a {World-Wide Web} {interface}, so a
	database can be queried and updated using a {web browser}.

	The ColdFusion Server application runs on the {web server} and
	has access to a {database}.  ColdFusion files on the web
	server are {HTML} pages with additional ColdFusion commands to
	{query} or {update} the database, written in {CFML}.  When the
	page is requested by the user, the {web server} passes the
	page to the Cold Fusion application, which executes the {CFML}
	commands, places the results of the {CFML} commands in the
	{HTML} file, and returns the page to the {web server}.  The
	page returned to the {web server} is now an ordinary {HTML}
	file, and it is sent to the user.

	Examples of ColdFusion applications include order entry, event
	registration, catalogue search, directories, calendars, and
	interactive training.  ColdFusion applications are robust
	because all database interactions are encapsulated in a single
	industrial-strength {CGI} script.  The formatting and
	presentation can be modified and revised at any time (as
	opposed to having to edit and recompile {source code}).

	ColdFusion Server can connect with any database that supports
	{ODBC} or {OLE DB} or one that has a native database driver.
	Native database drivers are available for {Oracle} and
	{Sybase} databases.

	ColdFusion is available for {Windows}, {Solaris}, and {HP-UX}.
	A {development environment} for creating ColdFusion files,
	called ColdFusion Studio, is also available for {Windows}.

	Current version: MX(6), as of 2003-07-11.

	The {filename extension} for ColdFusion files is .cfm

	{Home (http://www.coldfusion.com/)}.

	(2003-07-27)

1. A discrepancy between a computed, observed, or measured
	value or condition and the true, specified, or theoretically
	correct value or condition.

	2. <programming> A mental mistake made by a programmer that
	may result in a program {fault}.

	3. (verb) What a program does when it stops as result of a
	programming error.

	(2000-03-28)

<language, text> (XML) An initiative from the {W3C} defining
	an "extremely simple" dialect of {SGML} suitable for use on
	the {World-Wide Web}.

	{(http://www.w3.org/XML/)}.

	[Relationship to the {XSL} forthcoming subset of {DSSSL}?]

	(1997-11-20)

<architecture, processor> (CPU, processor) The part of a
	computer which controls all the other parts.  Designs vary
	widely but, in general, the CPU consists of the {control
	unit}, the {arithmetic and logic unit} (ALU) and memory
	({registers}, {cache}, {RAM} and {ROM}) as well as various
	temporary buffers and other logic.

	The control unit fetches instructions from memory and decodes
	them to produce signals which control the other part of the
	computer.  This may cause it to transfer data between memory
	and ALU or to activate {peripherals} to perform input or
	output.

	A {parallel computer} has several CPUs which may share other
	resources such as memory and peripherals.

	The term "processor" has to some extent replaced "CPU", though
	RAM and ROM are not normally considered as part of a
	processor.  This is particularly true of common modern
	{microprocessors} though there have been microprocessors which
	include RAM and/or ROM on the same {integrated circuit}.

	The {CPU Info Center} lists many kinds of CPU.

	(1998-10-21)

1. <file system> {hard link} or {symbolic link}.

	2. <hypertext> {hyperlink}.

	(1997-10-22)

1. Not operating.  "The up escalator is down" is considered a
	humorous thing to say, and "The elevator is down" always
	means "The elevator isn't working" and never refers to what
	floor the elevator is on.  With respect to computers, this
	term has passed into the mainstream; the extension to other
	kinds of machine is still hackish.

	2. "go down" To stop functioning; usually said of the
	{system}.  The message from the {console} that every hacker
	hates to hear from the operator is "System going down in 5
	minutes".

	3. "take down", "bring down" To deactivate purposely, usually
	for repair work or {PM}.  "I'm taking the system down to work
	on that bug in the tape drive."  Occasionally one hears the
	word "down" by itself used as a verb in this sense.

	See {crash}; opposite: {up}.

	[{Jargon File}]

	(1994-12-07)

<character> (From the colour it produces on white paper) Any
	contiguous sequence of {spaces}, {tabs}, {carriage returns},
	and/or {line feeds}.  Whitespace might also possibly include
	{form feed} characters.  The term is common on {Unix}.

	See also {non-printing character}.

	(1996-09-04)

<language, text> An {SGML}, {HTML}, or {XML} {token}
	representing the beginning (start tag: "<p ...>") or end (end
	tag: "</p>") of an {element}.  In normal SGML {syntax} (and
	always in {XML}), a tag starts with a "<" and ends with an
	">".

	In {HTML} jargon, the term "tag" is often used for an
	"{element}".

	(2001-01-31)

<object-oriented, programming> Improving a computer {program}
	by reorganising its internal structure without altering its
	external behaviour.

	When software developers add new features to a program, the
	code degrades because the original program was not designed
	with the extra features in mind.

	This problem could be solved by either rewriting the existing
	code or working around the problems which arise when adding
	the new features.  Redesigning a program is extra work, but
	not doing so would create a program which is more complicated
	than it needs to be.  Refactoring is a collection of
	techniques which have been designed to provide an alternative
	to the two situations mentioned above.

	The techniques enable programmers to restructure code so
	that the design of a program is clearer.  It also allows
	programmers to extract {reusable components}, streamline a
	program, and make additions to the program easier to
	implement.

	Refactoring is usually done by renaming {methods}, moving
	{fields} from one {class} to another, and moving code into a
	separate method.

	Although it is done using small and simple steps,
	refactoring a program will vastly improve its design and
	structure, making it easier to maintain and leading to
	more robust code.

	{"Refactoring, Reuse & Reality" by Bill Opdyke
	(http://st-www.cs.uiuc.edu/users/opdyke/wfo.990201.refac.html)}.

	{"Refactoring, a first example" by Martin Fowler
	(http://www.aw.com/cseng/titles/0-201-89542-0/vidrefact/vidrefact.html)}.

	(2001-05-02)

<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)

<programming> (Sometimes "var" /veir/ or /var/) A named memory
	location in which a program can store intermediate results and
	from which it can read it them.  Each {programming language}
	has different rules about how variables can be named, typed,
	and used.  Typically, a value is "assigned" to a variable in
	an {assignment} statement.  The value is obtained by
	evaluating an expression and then stored in the variable.  For
	example, the assignment

		x = y + 1

	means "add one to y and store the result in x".  This may look
	like a mathematical equation but the mathematical equality is
	only true in the program until the value of x or y changes.
	Furthermore, statements like

		x = x + 1

	are common.  This means "add one to x", which only makes sense
	as a state changing operation, not as a mathematical equality.

	The simplest form of variable corresponds to a single-{word}
	of {memory} or a {CPU} {register} and an assignment to a
	{load} or {store} {machine code} operation.

	A variable is usually defined to have a {type}, which never
	changes, and which defines the set of values the variable can
	hold.  A type may specify a single ("atomic") value or a
	collection ("aggregate") of values of the same or different
	types.  A common aggregate type is the {array} - a set of
	values, one of which can be selected by supplying a numerical
	{index}.

	Languages may be {untyped}, {weakly typed}, {strongly typed},
	or some combination.  {Object-oriented programming} languages
	extend this to {object} types or {classes}.

	A variable's {scope} is the region of the program source
	within which it represents a certain thing.  Scoping rules are
	also highly language dependent but most serious languages
	support both {local variables} and {global variables}.
	{Subroutine} and {function} {formal arguments} are special
	variables which are set automatically by the language runtime
	on entry to the subroutine.

	In a {functional programming} language, a variable's value
	never changes and change of state is handled as recursion over
	lists of values.

	(2004-11-16)

1. <character> {hash character}.

	2. <programming> {hash coding}.

	3. The preferred term for a {Perl} {associative array}.

	(1995-03-06)

<programming, tool> A program that converts another program
	from some {source language} (or {programming language}) to
	{machine language} (object code).  Some compilers output
	{assembly language} which is then converted to {machine
	language} by a separate {assembler}.

	A compiler is distinguished from an assembler by the fact that
	each input statement does not, in general, correspond to a
	single machine instruction or fixed sequence of instructions.
	A compiler may support such features as automatic allocation
	of variables, arbitrary arithmetic expressions, control
	structures such as FOR and WHILE loops, variable {scope},
	input/ouput operations, {higher-order functions} and
	{portability} of source code.

	{AUTOCODER}, written in 1952, was possibly the first primitive
	compiler.  {Laning and Zierler}'s compiler, written in
	1953-1954, was possibly the first true working algebraic
	compiler.

	See also {byte-code compiler}, {native compiler}, {optimising
	compiler}.

	(1994-11-07)

<communications> Any part of a signal that is not the true or
	original signal but is introduced by the communication
	mechanism.

	A common example would be an electrical signal travelling down
	a wire to which noise is added by inductive and capacitive
	coupling with other nearby signals (this kind of noise is
	known as "{crosstalk}").

	A less obvious form of noise is {quantisation} noise, such as
	the error between the true colour of a point in a scene in the
	real world and its representation as a {pixel} in a digital
	image.

	(2003-07-05)