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)

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. A set of function symbols with {arities}.

	2. <messaging> (Or sig) A few lines of information about the
	sender of an {electronic mail} message or {news} {posting}.
	Most {Unix} mail and news software will {automagically} append
	a signature from a file called .signature in the user's {home
	directory} to outgoing mail and news.

	A signature should give your real name and your {e-mail
	address} since, though these appear in the {headers} of your
	messages, they may be {munged} by intervening software.  It is
	currently (1994) hip to include the {URL} of your {home page}
	on the {World-Wide Web} in your sig.

	The composition of one's sig can be quite an art form,
	including an {ASCII} logo or one's choice of witty sayings
	(see {sig quote}, {fool file}).  However, large sigs are a
	waste of {bandwidth}, and it has been observed that the size
	of one's sig block is usually inversely proportional to one's
	prestige on the net.

	See also {doubled sig}, {sig virus}.

	2. <programming> A concept very similar to {abstract base
	classes} except that they have their own {hierarchy} and can
	be applied to compiled {classes}.  Signatures provide a means
	of separating {subtyping} and {inheritance}.  They are
	implemented in {C++} as patches to {GCC} 2.5.2 by Gerald
	Baumgartner <gb@cs.purdue.edu>.

	{(ftp://ftp.cs.purdue.edu/pub/gb/)}.

	(2001-01-05)

<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)

1. <character> {hash character}.

	2. <programming> {hash coding}.

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

	(1995-03-06)

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)