<data> A data structure holding many values, possibly of
	different types, which is usually accessed sequentially,
	working from the head to the end of the tail - an "ordered
	list".  This contrasts with a (one-dimensional) {array}, any
	element of which can be accessed equally quickly.

	Lists are often stored using a cell and pointer arrangement
	where each value is stored in a cell along with an associated
	pointer to the next cell.  A special pointer, e.g. zero, marks
	the end of the list.  This is known as a (singly) "linked
	list".  A doubly linked list has pointers from each cell to
	both next and previous cells.

	An unordered list is a {set}.

	(1998-11-12)

<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)

<programming> The name given in {Smalltalk} and other
	{object-oriented languages} to a procedure or routine
	associated with one or more {classes}.  An {object} of a
	certain class knows how to perform actions, e.g. printing
	itself or creating a new instance of itself, rather than the
	function (e.g. printing) knowing how to handle different types
	of object.

	Different classes may define methods with the same name
	(i.e. methods may be {polymorphic}).  The term "method" is used
	both for a named operation, e.g. "PRINT" and also for the code
	which a specific class provides to perform tha
	t operation.

	Most methods operate on objects that are instances of a
	certain class.  Some object-oriented languages call these
	"object methods" to distinguish then from "{class methods}".

	In {Smalltalk}, a method is defined by giving its name,
	documentation, temporary local variables and a sequence of
	expressions separated by "."s.

	(2000-03-22)

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)

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)

<programming> An individual {object} of a certain {class}.
	While a class is just the type definition, an actual usage of
	a class is called "instance".  Each instance of a class can
	have different values for its {instance variables}, i.e. its
	{state}.

	(1998-03-06)

<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. Not simulated.  Often used as a specific antonym to
	{virtual} in any of its jargon senses.

	2. <mathematics> {real number}.

	[{Jargon File}]

	(1997-03-12)

<language>

	1. A {relational language} designed by Jones and M. Sheeran in
	1986 for describing and designing circuits (a {hardware
	description language}).  Ruby programs denote {binary
	relations} and programs are built-up inductively from
	primitive relations using a pre-defined set of {relational
	operators}.  Ruby programs also have a geometric
	interpretation as networks of primitive relations connected by
	wires, which is important when layout is considered in circuit
	design.

	Ruby has been continually developed since 1986, and has been
	used to design many different kinds of circuits, including
	{systolic arrays}, {butterfly networks} and arithmetic
	circuits.

	{(ftp://ftp.cs.chalmers.se/pub/misc/ruby/)}.

	E-mail: <graham@cs.chalmers.se>.

	["Ruby - A Language of Relations and Higher-Order Functions",
	M. Sheeran, Proc 3rd Banff Workshop on Hardware Verification,
	Springer 1990].

	(1994-10-27)

	2. One of five pedagogical languages based on {Markov
	algorithms}, used in Higman's report (below).  The other
	languages are {Brilliant}, {Diamond}, {Nonpareil}, and
	{Pearl}.

	["Nonpareil, a Machine Level Machine Independent Language for
	the Study of Semantics", B. Higman, ULICS Intl Report No ICSI
	170, U London (1968)].

	(1994-10-27)

	3. A fully {object oriented} {interpreted} {scripting
	language} by Yukihiro Matsumoto <matz@netlab.co.jp>.

	Similar in scope to {Perl} and {Python}, Ruby has high-level
	{data types}, automatic {memory management}, {dynamic typing},
	a {module} system, {exceptions}, and a rich standard library.
	Other features are {CLU}-style {iterators} for {loop
	abstraction}, {singleton classes}/{methods} and {lexical
	closures}.

	In Ruby, everything is an {object}, including the basic data
	types.  For example, the number 1 is an instance of {class}
	Fixnum.

	Current version (stable): 1.6.7, as of 2002-03-01.

	{Ruby Home (http://www.ruby-lang.org/)}.

	{Ruby Central (http://www.rubycentral.com/)}.

	["Programming Ruby - The Pragmatic Programmer's Guide", David
	Thomas, Andrew Hunt, Yukihiro Matsumoto pub. Addison Wesley
	2000].

	(2002-06-19)

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. <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)

<data> A named value or relationship that exists for some or
	all {instances} of some {entity} and is directly associated
	with that instance.

	Examples include the {href} attribute of an {HTML} {anchor}
	element, the columns of a database table considered as
	attributes of each row, and the {members} ({properties} and
	{methods} of an {object} in {OOP}.  This contrasts with the
	contents of some kind of container (e.g. an array), which are
	typically not named.  The contents of an {associative array},
	though they might be considered to be named by their key
	values, are not normally thought of as attributes.

	(2001-02-04)