<World-Wide Web> (By analogy with "{applet}") A {Java} program
	that runs as part of a {network} service, typically an {HTTP
	server} and responds to requests from {clients}.

	The most common use for a servlet is to extend a {web server}
	by generating {web content} dynamically.  For example, a
	{client} may need {information} from a {database}; a servlet
	can be written that receives the request, gets and processes
	the data as needed by the {client} and then returns the result
	to the {client}.

	{Applets} are also written in {Java} but run inside the {JVM}
	of a {HTML} {browser} on the {client}.  Servlets and applets
	allow the server and client to be extended in a modular way by
	dynamically loading code which communicates with the main
	program via a standard programming interface.

	Servlets are more flexible than {CGI scripts} and, being
	written in {Java}, more portable.

	The spelling "servelet" is occasionally seen but {JavaSoft}
	spell it "servlet".  There is no such thing as a "serverlet".

	{(http://java.sun.com/products/servlet/)}.

	(2002-10-06)

<operating system, programming> The process of carrying out
	the {instructions} in a computer program by a computer.

	See also {dry run}.

	(1996-05-13)

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	write has been largely superseded by {talk} and then {irc}.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)

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)

<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)

<library, networking> {Unix} socket library routine to connect
	a socket that has been created on the local hosts to one at a
	specified socket address on the remote host.

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

	(1995-03-21)

<object-oriented> In {object-oriented programming}, an
	instance of the data structure and behaviour defined by the
	object's {class}.  Each object has its own values for the
	{instance variables} of its class and can respond to the
	{methods} defined by its class.

	For example, an object of the "Point" class might have
	instance variables "x" and "y" and might respond to the "plot"
	method by drawing a dot on the screen at those coordinates.

	(2004-01-26)

<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)

<World-Wide Web> (URL, previously "Universal") A {standard}
	way of specifying the location of an object, typically a {web
	page}, on the {Internet}.  Other types of object are described
	below.  URLs are the form of address used on the {World-Wide
	Web}.  They are used in {HTML} documents to specify the target
	of a {hyperlink} which is often another HTML document
	(possibly stored on another computer).

	Here are some example URLs:

	 http://www.w3.org/default.html
	 http://www.acme.co.uk:8080/images/map.gif
	 http://www.foldoc.org/?Uniform+Resource+Locator
	 http://www.w3.org/default.html#Introduction
	 ftp://wuarchive.wustl.edu/mirrors/msdos/graphics/gifkit.zip
	 ftp://spy:secret@ftp.acme.com/pub/topsecret/weapon.tgz
	 mailto:fred@doc.ic.ac.uk
	 news:alt.hypertext
	 telnet://dra.com

	The part before the first colon specifies the access scheme or
	{protocol}.  Commonly implemented schemes include: {ftp},
	{http} (World-Wide Web), {gopher} or {WAIS}.  The "file"
	scheme should only be used to refer to a file on the same
	host.  Other less commonly used schemes include {news},
	{telnet} or mailto ({e-mail}).

	The part after the colon is interpreted according to the
	access scheme.  In general, two slashes after the colon
	introduce a {hostname} (host:port is also valid, or for {FTP}
	user:passwd@host or user@host).  The {port} number is usually
	omitted and defaults to the standard port for the scheme,
	e.g. port 80 for HTTP.

	For an HTTP or FTP URL the next part is a {pathname} which is
	usually related to the pathname of a file on the server.  The
	file can contain any type of data but only certain types are
	interpreted directly by most {browsers}.  These include {HTML}
	and images in {gif} or {jpeg} format.  The file's type is
	given by a {MIME} type in the HTTP headers returned by the
	server, e.g. "text/html", "image/gif", and is usually also
	indicated by its {filename extension}.  A file whose type is
	not recognised directly by the browser may be passed to an
	external "viewer" {application}, e.g. a sound player.

	The last (optional) part of the URL may be a query string
	preceded by "?" or a "fragment identifier" preceded by "#".
	The later indicates a particular position within the specified
	document.

	Only alphanumerics, reserved characters (:/?#"<>%+) used for
	their reserved purposes and "$", "-", "_", ".", "&", "+" are
	safe and may be transmitted unencoded.  Other characters are
	encoded as a "%" followed by two {hexadecimal} digits.  Space
	may also be encoded as "+".  Standard {SGML} "&<name>;"
	character entity encodings (e.g. "&eacute;") are also accepted
	when URLs are embedded in HTML.  The terminating semicolon may
	be omitted if &<name> is followed by a non-letter character.

	{The authoritative W3C URL specification
	(http://www.w3.org/hypertext/WWW/Addressing/Addressing.html)}.

	(2000-02-17)

1. <operating system, software> The sequence of states of an
	executing {program}.  A process consists of the program {code}
	(which may be shared with other processes which are executing
	the same program), private data, and the state of the
	{processor}, particularly the values in its {registers}.  It
	may have other associated resources such as a {process
	identifier}, open files, {CPU time} limits, {shared memory},
	{child processes}, and {signal handlers}.

	One process may, on some {platforms}, consist of many
	{threads}.  A {multitasking} {operating system} can run
	multiple processes {concurrently} or in {parallel}, and allows
	a process to spawn "child" processes.

	(2001-06-16)

	2. <business> The sequence of activities, people, and systems
	involved in carrying out some business or achieving some
	desired result.  E.g. software development process, project
	management process, configuration management process.

	(2001-06-16)

<protocol> (HTTP) The {client-server} {TCP/IP} {protocol} used
	on the {World-Wide Web} for the exchange of {HTML} documents.
	It conventionally uses {port} 80.

	Current version: HTTP 1.1, defined in {RFC 2068}, as of May
	1997.

	See also {Uniform Resource Locator}.

	(1994-10-27)

<architecture> When one system performs in exactly the same
	way as another, though perhaps not at the same speed.  A
	typical example would be emulation of one computer by (a
	program running on) another.  You might use an emulation as a
	replacement for a system whereas you would use a simulation if
	you just wanted to analyse it and make predictions about it.

	(2003-05-22)

<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. A {cathode-ray tube} and associated electronics connected
	to a computer's video output.  A monitor may be either
	{monochrome} (black and white) or colour ({RGB}).  Colour
	monitors may show either digital colour (each of the red,
	green and blue signals may be either on or off, giving eight
	possible colours: black, white, red, green, blue, cyan,
	magenta and yellow) or analog colour (red, green and blue
	signals are continuously variable allowing any combination to
	be displayed).  Digital monitors are sometimes known as {TTL}
	because the voltages on the red, green and blue inputs are
	compatible with TTL logic chips.

	See also {gamut}, {multisync}, {visual display unit}.

	2. A programming language construct which encapsulates
	variables, access procedures and initialisation code within an
	abstract data type.  The monitor's variable may only be
	accessed via its access procedures and only one process may be
	actively accessing the monitor at any one time.  The access
	procedures are {critical sections}.  A monitor may have a
	queue of processes which are waiting to access it.

	3. A hardware device that measures electrical events such as
	pulses or voltage levels in a digital computer.

	4. To oversee a program during execution.  For example, the
	monitor function in the {Unix} {C} library enables profiling
	of a certain range of code addresses.  A histogram is produced
	showing how often the {program counter} was found to be at
	each position and how often each profiled function was called.

	{Unix} {man} page: monitor(3).

	5. A control program within the {operating system} that
	manages the allocation of system resources to active
	programs.

	6. A program that measures software performance.

<programming> (RMI) Part of the {Java} {programming language}
	{library} which enables a Java program running on one computer
	to access the {objects} and {methods} of another Java program
	running on a different computer.

	{Home
	(http://java.sun.com/products/jdk/1.1/docs/guide/rmi/index.html)}.

	(1997-09-04)

1. <networking> A deprecated term for a device that enables
	data to flow between different networks (forming an
	{internet}).

	Preferred terms are "{protocol converter}" (connects networks
	that use different {protocols}), "{router}" (connects two
	broadcast networks at layer 3 ({network layer}).  Another
	example is a {mail gateway}, which is a layer 7 ({application
	layer}) gateway.

	2. <hypertext> An {interface} between an information source
	and a {World-Wide Web} {server}.  {Common Gateway Interface}
	is a {standard} for such interfaces.  The information source
	can be any system that can be accessed by a program running on
	the web server.  A typical example is a {relational
	database}.

	(2000-05-24)

<programming> A computer system or process that requests a
	service of another computer system or process (a "{server}")
	using some kind of {protocol} and accepts the server's
	responses.  A client is part of a {client-server} software
	architecture.

	For example, a {workstation} requesting the contents of a file
	from a {file server} is a client of the file server.

	(1997-10-27)

<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)

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 program which provides some service to other ({client})
	programs.  The connection between client and server is
	normally by means of {message passing}, often over a
	{network}, and uses some {protocol} to encode the client's
	requests and the server's responses.  The server may run
	continuously (as a {daemon}), waiting for requests to arrive
	or it may be invoked by some higher level daemon which
	controls a number of specific servers ({inetd} on {Unix}).

	There are many servers associated with the {Internet}, such as
	those for {HTTP}, {Network File System}, {Network Information
	Service} (NIS), {Domain Name System} (DNS), {FTP}, {news},
	{finger}, {Network Time Protocol}.  On Unix, a long list can
	be found in /etc/services or in the {NIS} database "services".
	See {client-server}.

	2. A computer which provides some service for other computers
	connected to it via a network.  The most common example is a
	{file server} which has a local disk and services requests
	from remote clients to read and write files on that disk,
	often using {Sun}'s {Network File System} (NFS) {protocol} or
	{Novell Netware} on {PCs}.  Another common example is a {web
	server}.

	[{Jargon File}]

	(2003-12-29)