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)

<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)

<programming> A special value used in several languages to
	represent the thing referred to by an uninitialised pointer.

	<database> A special value that may be stored in some database
	columns to represent an unknown, missing, not applicable, or
	undefined value.  Nulls are treated completely differently
	from ordinary values when evaluating SQL expressions and there
	are several SQL constructs for dealing with nulls.

	(2003-06-17)

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)

<storage, architecture, jargon, theory> How something is; its
	configuration, attributes, condition, or information content.
	The state of a system is usually temporary (i.e. it changes
	with time) and volatile (i.e. it will be lost or reset to some
	initial state if the system is switched off).

	A state may be considered to be a point in some {space} of all
	possible states.  A simple example is a light, which is either
	on or off.  A complex example is the electrical activation in
	a human brain while solving a problem.

	In computing and related fields, states, as in the light
	example, are often modelled as being {discrete} (rather than
	continuous) and the transition from one state to another is
	considered to be instantaneous.  Another (related) property of
	a system is the number of possible states it may exhibit.
	This may be finite or infinite.  A common model for a system
	with a finite number of discrete state is a {finite state
	machine}.

	[{Jargon File}]

	(1996-10-13)

<language, tool> A {Unix} tool written in {Tcl} and a {script
	language} for automating the operation of {interactive}
	applications such as {telnet}, {FTP}, {passwd}, {fsck},
	{rlogin}, {tip}, etc..  Expect can feed input to other
	programs and perform {pattern matching} on their output.  It
	is also useful for testing these applications.  By adding
	{Tk}, you can also wrap interactive applications in {X11}
	{GUIs}.

	{Home (http://expect.nist.gov/)}.

	["expect: Scripts for Controlling Interactive Tasks", Don
	Libes, Comp Sys 4(2), U Cal Press Journals, Nov 1991].

	(1997-06-09)

(Or "primitive") A built-in function or operator is one
	provided by the lowest level of a language implementation.
	This usually means it is not possible (or efficient) to
	express it in the language itself.  Typical examples are the
	basic arithmetic and {Boolean} operators (in {C} syntax: +, -,
	*, /, %, !, &&, ||), bit manipulation operators (~, &, |, ^)
	and I/O primitives.  Other common functions may be provided in
	libraries but are not built-in if they are written in the
	language being implemented.

	(1995-02-14)

An error condition that changes the normal {flow of control}
	in a program.  An exception may be generated ("raised") by
	{hardware} or {software}.  Hardware exceptions include
	{reset}, {interrupt} or a signal from a {memory management
	unit}.  Exceptions may be generated by the {arithmetic logic
	unit} or {floating-point unit} for numerical errors such as
	divide by zero, {overflow} or {underflow} or {instruction
	decoding} errors such as privileged, reserved, {trap} or
	undefined instructions.  Software exceptions are even more
	varied and the term could be applied to any kind of error
	checking which alters the normal behaviour of the program.

	(1994-10-31)

<programming> A symbol used as a {function}, with {infix
	syntax} if it has two arguments (e.g. "+") or {prefix syntax} if
	it has only one (e.g. {Boolean} NOT).  Many languages use
	operators for built-in functions such as arithmetic and logic.

	(1995-04-30)

1. <unit, text> (Sometimes abbreviated "pt") The unit of
	length used in {typography} to specify text character height,
	{rule} width, and other small measurements.

	There are six slightly different definitions: {Truchet point},
	{Didot point}, {ATA point}, {TeX point}, {Postscript point},
	and {IN point}.

	In Europe, the most commonly used is Didot and in the US, the
	formerly standard ATA point has essentially been replaced by
	the PostScript point due to the demise of traditional
	typesetting systems and rise of desktop computer based systems
	running software such as {QuarkXPress}, {Adobe InDesign} and
	{Adobe Pagemaker}.

	There are 20 {twips} in a point and 12 points in a {pica}
	(known as a "Cicero" in the Didot system).

	{Different point systems
	(http://www.vakcer.com/oberon/dtp/fonts/point.htm)}.

	(2004-12-23)

	2. <hardware> To move a {pointing device} so that the
	on-screen pointer is positioned over a certain object on the
	screen such as a {button} in a {graphical user interface}.  In
	most {window systems} it is then necessary to {click} a
	(physical) button on the pointing device to activate or select
	the object.  In some systems, just pointing to an object is
	known as "mouse-over" {event} which may cause some help text
	(called a "tool tip" in {Windows}) to be displayed.

	(2001-05-21)

<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)

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)

A group G is a non-empty {set} upon which a {binary} operator
	* is defined with the following properties for all a,b,c in G:

	  Closure:     G is closed under *,  a*b in G
	  Associative: * is associative on G, (a*b)*c = a*(b*c)
	  Identity:    There is an identity element  e  such that
		       a*e = e*a = a.
	  Inverse:     Every element has a unique inverse a' such that
		       a * a' = a' * a = e.  The inverse is usually
		       written with a superscript -1.

	(1998-10-03)

<mathematics, data> The {ancestor} {node} in a {tree} that
	points to the current node (one of its child nodes).

	(2005-09-15)

<file system> An element of data storage in a {file system}.

	The history of computing is rich in varied kinds of files and
	{file systems}, whether ornate (e.g., {Macintosh file system}
	for a well-known case) or deficient (e.g., many simple
	pre-1980s file systems don't allow {directories}).

	However, the prototypical file has these characteristics:

	* It is a single sequence of bytes (but consider {Macintosh}
	{resource forks}).

	* It has a finite length, unlike, e.g. a {Unix} {device}.

	* It is stored in a {non-volatile storage} medium (but see
	{ramdrive}).

	* It exists (nominally) in a {directory}.

	* It has a name that it can be referred to by in file
	operations, possibly in combination with its {path}.

	Additionally, a file system may associate other information
	with a file, such as {permission} bits or other {file
	attributes}; timestamps for file creation, last revision, and
	last access; revision numbers (a` la VMS), and other kinds of
	{magic}.

	Compare: {document}.

	(1997-04-08)

1. <networking> A {bang path} or explicitly routed {Internet
	address}; a node-by-node specification of a link between two
	machines.

	2. <file system> {pathname}.

	3. <operating system>  The list of directories the kernel
	(under {Unix}) or the command interpreter (under {MS-DOS})
	searches for {executables}.  It is stored as part of the
	{environment} in both operating systems.

	Other, similar constructs abound under Unix; the {C}
	{preprocessor}, for example, uses such a search path to locate
	"#include" files.

	[{Jargon File}]

	(1996-11-21)

<operating system> A list from which the user may select an
	operation to be performed.  This is often done with a {mouse}
	or other pointing device under a {graphical user interface}
	but may also be controlled from the keyboard.

	Menus are very convenient for beginners because they show what
	commands are available and make experimentating with a new
	program easy, often reducing the need for user documentation.
	Experienced users however, often prefer keyboard commands,
	especially for frequently user operations, because they are
	faster to use.  In situations such as text entry where the
	keyboard must be used anyway, having to move your hand to the
	mouse to invoke a menu operation is slow.

	There are many different ways of presenting menus but the most
	common are the {menu bar} (with {pull-down menus}) and the
	{context-sensitive menu}.

	The term "menu" tends to be reserved for a list of actions or
	global options, whereas a "{list box}" or other graphical
	{widget} might present any kind of choice.

	See also {menuitis}.

	(1994-12-02)

<software> (Or "option", "flag", "switch", "option switch") An
	argument to a command that modifies its function rather than
	providing data.  Options generally start with "-" in {Unix} or
	"/" in {MS-DOS}.  This is usually followed by a single letter
	or occasionally a digit.

	Some commands require each option to be a separate argument,
	introduced by a new "-" or "/", others allow multiple option
	letters to be concatenated into a single argument with a
	single "-" or "/", e.g. "ls -al".  A few Unix commands
	(e.g. {ar}, {tar}) allow the "-" to be omitted.  Some options
	may or must be followed by a value, e.g. "cc prog.c -o prog",
	sometimes with and sometimes without an intervening space.

	{getopt} and {getopts} are commands for parsing command line
	options.  There is also a {C} library routine called getopt
	for the same purpose.

	(1996-12-11)

<hypertext> A program which allows a person to read
	{hypertext}.  The browser gives some means of viewing the
	contents of {nodes} (or "pages") and of {navigating} from one
	node to another.

	{Netscape Navigator}, {NCSA} {Mosaic}, {Lynx}, and {W3} are
	examples for browsers for the {World-Wide Web}.  They act as
	{clients} to remote {web servers}.

	(1996-05-31)

1. A new or better version of some {hardware} or {software}.

	Often used in {marketroid}-speak to mean "{bug fix}".

	2. The act of developing or installing a new version.

	(1995-03-14)

<World-Wide Web> A user's reference to a document on the
	{World-Wide Web} or other hypermedia system, usually in the
	form of a {URL} and a title or comment string.

	Most World-Wide Web and {Gopher} {browsers} can save and load
	a file of bookmarks to allow you to quickly locate documents
	to which you want to refer again.

	(1997-06-09)

<networking> 1. A lasting connection between a user (or user
	agent) and a {peer}, typically a {server}, usually involving
	the exchange of many packets between the user's computer and
	the server.  A session is typically implemented as a layer in
	a network {protocol} (e.g. {telnet}, {FTP}).

	In the case of protocols where there is no concept of a
	session layer (e.g. {UDP}) or where sessions at the {session
	layer} are generally very short-lived (e.g. {HTTP}), {virtual}
	sessions are implemented by having each exchange between the
	user and the remote host include some form of {cookie} which
	stores state (e.g. a unique session ID, information about the
	user's preferences or authorisation level, etc.).

	See also {login}.

	2. A lasting connection using the {session layer} of a
	networking protocol.

	(1997-08-03)

<algorithm, programming> A detailed sequence of actions to
	perform to accomplish some task.  Named after an Iranian
	mathematician, Al-Khawarizmi.

	Technically, an algorithm must reach a result after a {finite}
	number of steps, thus ruling out {brute force} search methods
	for certain problems, though some might claim that brute force
	search was also a valid (generic) algorithm.  The term is also
	used loosely for any sequence of actions (which may or may not
	terminate).

	{Paul E. Black's Dictionary of Algorithms, Data Structures,
	and Problems (http://www.nist.gov/dads/)}.

	(2002-02-05)

<programming> A sequence of {data} values, usually {bytes},
	which usually stand for {characters} (a "character string").
	The {mapping} between values and characters is determined by
	the {character set} which is itself specified implcitly or
	explicitly by the environment in which the string is being
	interpreted.

	The most common character set is {ASCII} but, since the late
	1990s, there has been increased interest in larger character
	sets such as {Unicode} where each character is represented by
	more than eight {bits}.

	Most programming languages consider strings (e.g.
	"124:shabooya:\n", "hello world") basically distinct from
	numbers which are typically stored in fixed-length {binary} or
	{floating-point} representation.

	A {bit string} is a sequence of {bits}.

	(1999-12-21)

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

	2. <hypertext> {hyperlink}.

	(1997-10-22)

<programming> To process a {node} while {traversing} a
	{graph}.

	(2001-09-30)

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)

<programming> Any piece of program code in a {high-level
	language} which, when (if) its execution terminates, returns a
	value.  In most programming languages, expressions consist of
	constants, variables, operators, functions, and {parentheses}.
	The operators and functions may be built-in or user defined.
	Languages differ on how expressions of different {types} may
	be combined - with some combination of explicit {casts} and
	implicit {coercions}.

	The {syntax} of expressions generally follows conventional
	mathematical notation, though some languages such as {Lisp} or
	{Forth} have their own idiosyncratic syntax.

	(2001-05-14)

<operating system> All activities involved in completing any
	project on a computer from start to finish.  A job may involve
	several {processes} and several {programs}.

	This term originates from a time when a user would manually
	submit a job as a deck of {punched cards} which would
	typically include {source code} interspersed with {job control
	language} instructions to guide phases of the job such as
	{compilation}, {linking}, {execution} and printing.

	(2005-03-16)

1. <messaging> One point-to-point transmission in a series
	required to get a message from point A to point B on a {store
	and forward} network.  On such networks (including {UUCPNET}
	and {FidoNet}), an important inter-machine metric is the hop
	count of the shortest path between them.  This can be more
	significant than their geographical separation.

	Each {exclamation mark} in a {bang path} represents one hop.

	2. <networking> One direct host-to-host connection forming
	part of the route between two hosts in a {routed} {network}
	such as the {Internet}.  Some {protocols} place an upper limit
	on the hop count in order to detect routing loops.

	3. <jargon, networking> To {log in} to a {remote} computer,
	especially via {rlogin} or {telnet}.  "I'll hop over to foovax
	to FTP that."

	[{Jargon File}]

	(1997-06-25)

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)

<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. <World-Wide Web> {Active Server Pages}.

	2. <networking> {application service provider}.

	3. <language> A {query language}(?).

	[Sammet 1969, p.702].

	4. <processor> {Attached Support Processor}.

	(2000-07-08)

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)

<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)

<testing> The process of exercising a product to identify
	differences between expected and actual behaviour.  Typically
	testing is bottom-up: {unit testing} and {integration testing}
	by developers, {system testing} by testers, and {user
	acceptance testing} by users.

	{Test coverage} attempts to assess how complete a test has
	been.

	2. The second stage in a {generate and test} search
	{algorithm}.

	[{Jargon File}]

	(2003-09-24)

1. <hardware> A generic term for a {display device} that shows
	text and/or images on a roughly flat rectangular surface.  The
	most common type is usually refered to as a "{monitor}" and is
	based on a {cathode-ray tube}, though {flat panel} displays
	have, since around 2000, become increasingly competitive in
	price and performance.

	(2005-07-28)

	2. A {screen multiplexer} utility which lets you run multiple
	{interactive} {terminal sessions} (and {curses} programs)
	through a single terminal connection (on one {virtual
	console}, one terminal, through one {modem} link, {telnet}
	session or {xterm}).

	Screen can detach processes from one terminal and attach them
	to another.  "Auto-detach" lets you continue working after
	being disconnected and reconnected.  It supports keyboard
	driven cut and paste from any text and/or curses application
	(like {Lynx}) to any other (like {xemacs}).

	Screen comes with many {Linux} distributions and is available
	(free) on many other {Unix} {platforms}.

	(2005-07-29)

<library, networking> {Berkeley} {Unix} networking {socket}
	library routine to satisfy a connection request from a remote
	{host}.  A specified socket on the local host (which must be
	capable of accepting the connection) is connected to the
	requesting socket on the remote host.  The remote socket's
	socket address is returned.

	{Unix manual pages}: accept(2), connect(2).

	(1994-11-08)

[WPI] 1. Badly written or functionally poor, e.g. a program
	that is very difficult to use because of gratuitously poor
	design decisions.  Opposite: {cuspy}.

	2. Anything that manipulates a shared resource without regard
	for its other users in such a way as to cause a (non-fatal)
	problem.  Examples: programs that change tty modes without
	resetting them on exit, or windowing programs that keep
	forcing themselves to the top of the window stack.  Compare
	{all-elbows}.

	[{Jargon File}]

	(1994-10-27)

<programming> The multiple kilograms of macerated, pounded,
	steamed, bleached, and pressed trees that accompany most
	modern software or hardware products (see also {tree-killer}).
	Hackers seldom read paper documentation and (too) often resist
	writing it; they prefer theirs to be terse and {on-line}.  A
	common comment on this predilection is "You can't {grep} dead
	trees".

	See {drool-proof paper}, {verbiage}, {treeware}.

	[{Jargon File}]

	(2003-10-25)

1. <electronics> {push-button}.

	2. <operating system> A graphical representation of an
	electrical {push-button} appearing as part of a {graphical
	user interface}.  Moving the {mouse pointer} over the
	graphical button and pressing one of the physical mouse
	buttons starts some software action such as closing a window
	or deleting a file.

	See also {radio button}.

	(1997-07-07)

(Plural "indices" or "indexes")

	1. <programming> A number used to select an element of a list,
	vector, {array} or other sequence.  Such indices are nearly
	always non-negative integers but see {associative array}.

	2. <database> See {inverted index}.  [Other kinds?]

	3. <World-Wide Web> A {search engine}.

	4. <World-Wide Web> A {subject index}.

	4. <jargon> See {coefficient of X}.

	[{Jargon File}]

	(1997-04-09)

<jargon> /foo/ A sample name for absolutely anything,
	especially programs and files (especially {scratch files}).
	First on the standard list of {metasyntactic variables} used
	in {syntax} examples.  See also {bar}, {baz}, {qux}, {quux},
	{corge}, {grault}, {garply}, {waldo}, {fred}, {plugh},
	{xyzzy}, {thud}.

	The etymology of "foo" is obscure.  When used in connection
	with "bar" it is generally traced to the WWII-era Army slang
	acronym {FUBAR}, later bowdlerised to {foobar}.

	However, the use of the word "foo" itself has more complicated
	antecedents, including a long history in comic strips and
	cartoons.

	"FOO" often appeared in the "Smokey Stover" comic strip by
	Bill Holman.  This surrealist strip about a fireman appeared
	in various American comics including "Everybody's" between
	about 1930 and 1952.  FOO was often included on licence plates
	of cars and in nonsense sayings in the background of some
	frames such as "He who foos last foos best" or "Many smoke but
	foo men chew".

	Allegedly, "FOO" and "BAR" also occurred in Walt Kelly's
	"Pogo" strips.  In the 1938 cartoon "The Daffy Doc", a very
	early version of Daffy Duck holds up a sign saying "SILENCE IS
	FOO!".  Oddly, this seems to refer to some approving or
	positive affirmative use of foo.  It has been suggested that
	this might be related to the Chinese word "fu" (sometimes
	transliterated "foo"), which can mean "happiness" when spoken
	with the proper tone (the lion-dog guardians flanking the
	steps of many Chinese restaurants are properly called "fu
	dogs").

	Earlier versions of this entry suggested the possibility that
	hacker usage actually sprang from "FOO, Lampoons and Parody",
	the title of a comic book first issued in September 1958, a
	joint project of Charles and Robert Crumb.  Though Robert
	Crumb (then in his mid-teens) later became one of the most
	important and influential artists in underground comics, this
	venture was hardly a success; indeed, the brothers later
	burned most of the existing copies in disgust.  The title FOO
	was featured in large letters on the front cover.  However,
	very few copies of this comic actually circulated, and
	students of Crumb's "oeuvre" have established that this title
	was a reference to the earlier Smokey Stover comics.

	An old-time member reports that in the 1959 "Dictionary of the
	TMRC Language", compiled at {TMRC} there was an entry that
	went something like this:

	FOO: The first syllable of the sacred chant phrase "FOO MANE
	PADME HUM."  Our first obligation is to keep the foo counters
	turning.

	For more about the legendary foo counters, see {TMRC}.  Almost
	the entire staff of what became the {MIT} {AI LAB} was
	involved with TMRC, and probably picked the word up there.

	Another correspondant cites the nautical construction
	"foo-foo" (or "poo-poo"), used to refer to something
	effeminate or some technical thing whose name has been
	forgotten, e.g. "foo-foo box", "foo-foo valve".  This was
	common on ships by the early nineteenth century.

	Very probably, hackish "foo" had no single origin and derives
	through all these channels from Yiddish "feh" and/or English
	"fooey".

	[{Jargon File}]

	(1998-04-16)

1. (Obsolete) The source code for a program, which may be in
	any language, as opposed to the linkable or executable binary
	produced from it by a compiler.  The idea behind the term is
	that to a real hacker, a program written in his favourite
	programming language is at least as readable as English.
	Usage: mostly by old-time hackers, though recognisable in
	context.

	2. The official name of the {database} language used by the
	{Pick} {operating system}, actually a sort of {crufty},
	brain-damaged {SQL} with delusions of grandeur.  The name
	permits {marketroids} to say "Yes, and you can program our
	computers in English!" to ignorant {suits} without quite
	running afoul of the truth-in-advertising laws.

	["Exploring the Pick Operating System", J.E. Sisk et al,
	Hayden 1986].

	[{Jargon File}]

<artificial intelligence, information science> The objects,
	concepts and relationships that are assumed to exist in some
	area of interest.  A collection of {knowledge}, represented
	using some {knowledge representation} language is known as a
	{knowledge base} and a program for extending and/or querying a
	knowledge base is a {knowledge-based system}.

	Knowledge differs from {data} or {information} in that new
	knowledge may be created from existing knowledge using logical
	{inference}.  If information is data plus meaning then
	knowledge is information plus processing.

	A common form of knowledge, e.g. in a {Prolog} program, is a
	collection of {facts} and {rules} about some subject.

	For example, a {knowledge base} about a family might contain
	the facts that John is David's son and Tom is John's son and
	the rule that the son of someone's son is their grandson.
	From this knowledge it could infer the new fact that Tom is
	David's grandson.

	See also {Knowledge Level}.

	(1994-10-19)

1. <networking> {e-mail address}.

	2. <networking> {Internet address}.

	3. <networking> {MAC address}.

	4. <storage, programming> An unsigned integer used to select
	one fundamental element of storage, usually known as a {word}
	from a computer's {main memory} or other storage device.  The
	{CPU} outputs addresses on its {address bus} which may be
	connected to an {address decoder}, {cache controller}, {memory
	management unit}, and other devices.

	While from a hardware point of view an address is indeed an
	integer most {strongly typed} programming languages disallow
	mixing integers and addresses, and indeed addresses of
	different data types.  This is a fine example for {syntactic
	salt}: the compiler could work without it but makes writing
	bad programs more difficult.

	(1997-07-01)

<logic> (=> or a thin right arrow) A binary {Boolean} function
	and {logical connective}.  A => B is true unless A is true and
	B is false.  The {truth table} is

		A B | A => B
		----+-------
		F F |   T
		F T |   T
		T F |   F
		T T |   T

	It is surprising at first that A => B is always true if A is
	false, but if X => Y then we would expect that (X & Z) => Y
	for any Z.

	(1995-09-30)