<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)

<database, programming> (JDBC) Part of the {Java Development
	Kit} which defines an {application programming interface} for
	{Java} for standard {SQL} access to {databases} from Java
	{programs}.

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

	{FAQ (http://www.yoyoweb.com/Javanese/JDBC/FAQ.html)}.

	See also {Open Database Connectivity}.

	(1997-09-04)

A {relational DBMS} vendor.

1. <database> One or more large structured sets of persistent
	data, usually associated with software to update and {query}
	the data.  A simple database might be a single file containing
	many {records}, each of which contains the same set of
	{fields} where each field is a certain fixed width.

	A database is one component of a {database management system}.

	See also {ANSI/SPARC Architecture}, {atomic}, {blob}, {data
	definition language}, {deductive database}, {distributed
	database}, {fourth generation language}, {functional
	database}, {object-oriented database}, {relational database}.

	{Carol E. Brown's tutorial
	(http://accounting.rutgers.edu/raw/aies/www.bus.orst.edu/faculty/brownc/lectures/db_tutor/db_tutor.htm)}.

	2. <hypertext> A collection of {nodes} managed and stored in
	one place and all accessible via the same {server}.  {Links}
	outside this are "external", and those inside are "internal".

	On the {World-Wide Web} this is called a {website}.

	3. All the facts and rules comprising a {logic programming}
	program.

	(2005-11-17)

1. The {supervisor} program or {operating system} on a
	computer.

	2. The entire computer system, including input/output devices,
	the {supervisor} program or {operating system} and possibly
	other {software}.

	3. Any large program.

	4. Any method or {algorithm}.

	[{Jargon File}]

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)

<standard, database> (ODBC) A {standard} for accessing
	different {database} systems.  There are interfaces for
	{Visual Basic}, {Visual C++}, {SQL} and the ODBC driver pack
	contains drivers for the {Access}, {Paradox}, {dBase}, Text,
	{Excel} and {Btrieve} databases.

	An application can submit statements to ODBC using the ODBC
	flavor of SQL.  ODBC then translates these to whatever flavor
	the database understands.

	ODBC 1.0 was released in September 1992.

	ODBC is based on {Call-Level Interface} and was defined by the
	{SQL Access Group}.  {Microsoft} was one member of the group
	and was the first company to release a commercial product
	based on its work (under {Microsoft Windows}) but ODBC is not
	a Microsoft standard (as many people believe).

	ODBC drivers and development tools are available now for
	{Microsoft Windows}, {Unix}, {OS/2}, and {Macintosh}.

	[On-line document?]

	["Unix Review", Aug 1995].

	(1996-05-27)

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)

1. <networking> A computer connected to a {network}.

	The term {node} includes devices such as routers and printers
	which would not normally be called "hosts".

	2. <communications> A computer to which one connects using a
	{terminal emulator}.

	(1995-02-16)

<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)

A language proposed by Cii {Honeywell-Bull} to meet the DoD
	{Ironman} requirements which led to {Ada}.  This language won
	in 1979.

	["On the GREEN Language Submitted to the DoD", E.W. Dijkstra,
	SIGPLAN Notices 13(10):16-21 (Oct 1978)].

	(1994-12-02)

<database> (DBMS) A suite of programs which typically manage
	large structured sets of persistent data, offering ad hoc
	query facilities to many users.  They are widely used in
	business applications.

	A database management system (DBMS) can be an extremely
	complex set of software programs that controls the
	organisation, storage and retrieval of data (fields, records
	and files) in a database.  It also controls the security and
	integrity of the database.  The DBMS accepts requests for data
	from the application program and instructs the operating
	system to transfer the appropriate data.

	When a DBMS is used, information systems can be changed much
	more easily as the organisation's information requirements
	change.  New categories of data can be added to the database
	without disruption to the existing system.

	Data security prevents unauthorised users from viewing or
	updating the database.  Using passwords, users are allowed
	access to the entire database or subsets of the database,
	called subschemas (pronounced "sub-skeema").  For example, an
	employee database can contain all the data about an individual
	employee, but one group of users may be authorised to view
	only payroll data, while others are allowed access to only
	work history and medical data.

	The DBMS can maintain the integrity of the database by not
	allowing more than one user to update the same record at the
	same time.  The DBMS can keep duplicate records out of the
	database; for example, no two customers with the same customer
	numbers (key fields) can be entered into the database.

	{Query languages} and {report writers} allow users to
	interactively interrogate the database and analyse its data.

	If the DBMS provides a way to interactively enter and update
	the database, as well as interrogate it, this capability
	allows for managing personal databases.  However, it may not
	leave an audit trail of actions or provide the kinds of
	controls necessary in a multi-user organisation.  These
	controls are only available when a set of application programs
	are customised for each data entry and updating function.

	A business information system is made up of subjects
	(customers, employees, vendors, etc.) and activities (orders,
	payments, purchases, etc.).  Database design is the process of
	deciding how to organize this data into record types and how
	the record types will relate to each other.  The DBMS should
	mirror the organisation's data structure and process
	transactions efficiently.

	Organisations may use one kind of DBMS for daily transaction
	processing and then move the detail onto another computer that
	uses another DBMS better suited for random inquiries and
	analysis.  Overall systems design decisions are performed by
	data administrators and systems analysts.  Detailed database
	design is performed by database administrators.

	The three most common organisations are the {hierarchical
	database}, {network database} and {relational database}.  A
	database management system may provide one, two or all three
	methods.  Inverted lists and other methods are also used.  The
	most suitable structure depends on the application and on the
	transaction rate and the number of inquiries that will be
	made.

	Database machines are specially designed computers that hold
	the actual databases and run only the DBMS and related
	software.  Connected to one or more mainframes via a
	high-speed channel, database machines are used in large volume
	transaction processing environments.  Database machines have a
	large number of DBMS functions built into the hardware and
	also provide special techniques for accessing the disks
	containing the databases, such as using multiple processors
	concurrently for high-speed searches.

	The world of information is made up of data, text, pictures
	and voice.  Many DBMSs manage text as well as data, but very
	few manage both with equal proficiency.  Throughout the 1990s,
	as storage capacities continue to increase, DBMSs will begin
	to integrate all forms of information.  Eventually, it will be
	common for a database to handle data, text, graphics, voice
	and video with the same ease as today's systems handle data.

	See also: {intelligent database}.

	(1998-10-07)

<programming> An {object} adhering to a {component
	architecture}.

	(1997-11-20)

1. To prepare to read or write a file.  This usually involves
	checking whether the file already exists and that the user has
	the necessary authorisation to read or write it.  The result
	of a successful open is usually some kind of {capability}
	(e.g. a {Unix} {file descriptor}) - a token that the user
	passes back to the system in order to access the file without
	further checks and finally to close the file.

	2. Abbreviation for "open (or left) parenthesis" - used when
	necessary to eliminate oral ambiguity.  To read aloud the LISP
	form (DEFUN FOO (X) (PLUS X 1)) one might say: "Open defun
	foo, open eks close, open, plus eks one, close close."

	3. Non-proprietary.  An open {standard} is one which can be
	used without payment.

	[{Jargon File}]

	(1995-01-31)

<language, programming> (Or "source", or rarely "source
	language") The form in which a computer program is written by
	the programmer.  Source code is written in some formal
	programming language which can be compiled automatically into
	{object code} or {machine code} or executed by an
	{interpreter}.

	(1995-01-05)

<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)

(From the technical term "logical device", wherein a physical
	device is referred to by an arbitrary "logical" name) Having
	the role of.  If a person (say, Les Earnest at SAIL) who had
	long held a certain post left and were replaced, the
	replacement would for a while be known as the "logical" Les
	Earnest.  (This does not imply any judgment on the
	replacement).

	Compare {virtual}.

	At Stanford, "logical" compass directions denote a coordinate
	system in which "logical north" is toward San Francisco,
	"logical west" is toward the ocean, etc., even though logical
	north varies between physical (true) north near San Francisco
	and physical west near San Jose.  (The best rule of thumb here
	is that, by definition, El Camino Real always runs logical
	north-and-south.)  In giving directions, one might say: "To
	get to Rincon Tarasco restaurant, get onto {El Camino Bignum}
	going logical north."  Using the word "logical" helps to
	prevent the recipient from worrying about that the fact that
	the sun is setting almost directly in front of him.  The
	concept is reinforced by North American highways which are
	almost, but not quite, consistently labelled with logical
	rather than physical directions.

	A similar situation exists at MIT: Route 128 (famous for the
	electronics industry that has grown up along it) is a
	3-quarters circle surrounding Boston at a radius of 10 miles,
	terminating near the coastline at each end.  It would be most
	precise to describe the two directions along this highway as
	"clockwise" and "counterclockwise", but the road signs all say
	"north" and "south", respectively.  A hacker might describe
	these directions as "logical north" and "logical south", to
	indicate that they are conventional directions not
	corresponding to the usual denotation for those words.  (If
	you went logical south along the entire length of route 128,
	you would start out going northwest, curve around to the
	south, and finish headed due east, passing along one infamous
	stretch of pavement that is simultaneously route 128 south and
	Interstate 93 north, and is signed as such!)

	[{Jargon File}]

	(1995-01-24)

<digital signal processing> The result of measuring the
	amplitude of an analog signal at a specified time.  In
	{digital signal processing} a sample is a signed or unsigned
	number and the number of samples per second is called the
	{sample rate}.

	(2001-06-06)

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)

1. <unit> A unit of data or memory, often, but not
	exclusively, on a {magnetic disk} or {magnetic tape}.

	Compare {record}, {sector}.

	(2000-07-17)

	2. <operating system> To delay or sit idle while waiting for
	something.

	Compare {busy-wait}.

	(2000-07-17)

	3. <programming> A delimited section of {source code} in a
	{block-structured} language.

	(2004-09-29)

1. <mathematics> A {function}, f : A -> B, is injective or
	one-one, or is an injection, if and only if

		for all a,b in A, f(a) = f(b) => a = b.

	I.e. no two different inputs give the same output (contrast
	many-to-one).  This is sometimes called an embedding.  Only
	injective functions have left inverses f' where f'(f(x)) = x,
	since if f were not an injection, there would be elements of B
	for which the value of f' was not unique.  If an injective
	function is also a {surjection} then is it a {bijection}.

	2. <reduction> An injection function is one which takes
	objects of type T and returns objects of type C(T) where C is
	some {type constructor}.  An example is

		f x = (x, 0).

	The opposite of an injection function is a {projection}
	function which extracts a component of a constructed object,
	e.g.

		fst (x,y) = x.

	We say that f injects its argument into the data type and fst
	projects it out.

	(1995-03-14)