After-sale handholding; something many software vendors
	promise but few deliver.  To hackers, most support people are
	useless - because by the time a hacker calls support he or she
	will usually know the software and the relevant manuals better
	than the support people (sadly, this is *not* a joke or
	exaggeration).  A hacker's idea of "support" is a tte--tte
	or exchange of {electronic mail} with the software's designer.

	[{Jargon File}]

	(1995-02-15)

1. {application program}.

	2. {function application}.

<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)

<language, database, standard> /S Q L/ An industry-standard
	language for creating, updating and, querying {relational
	database management systems}.

	SQL was developed by {IBM} in the 1970s for use in {System R}.
	It is the {de facto standard} as well as being an {ISO} and
	{ANSI} {standard}.  It is often embedded in general purpose
	programming languages.

	The first SQL standard, in 1986, provided basic language
	constructs for defining and manipulating {tables} of data; a
	revision in 1989 added language extensions for {referential
	integrity} and generalised {integrity} {constraints}.  Another
	revision in 1992 provided facilities for {schema} manipulation
	and {data administration}, as well as substantial enhancements
	for data definition and data manipulation.

	Development is currently underway to enhance SQL into a
	computationally complete language for the definition and
	management of {persistent}, complex objects.  This includes:
	generalisation and specialisation hierarchies, {multiple
	inheritance}, user defined {data types}, {triggers} and
	{assertions}, support for {knowledge based systems},
	{recursive query expressions}, and additional data
	administration tools.  It also includes the specification of
	{abstract data types} (ADTs), object identifiers, {methods},
	{inheritance}, {polymorphism}, {encapsulation}, and all of the
	other facilities normally associated with object data
	management.

	The emerging {SQL3} standard is expected to be complete in
	1998.

	According to Allen G. Taylor, SQL does _not_ stand for
	"Structured Query Language".  That, like "SEQUEL" (and its
	pronunciation /see'kw*l/), was just another unofficial name
	for a precursor of SQL.  However, the IBM SQL Reference manual
	for DB2 and Craig Mullins's "DB2 Developer's Guide" say SQL
	_does_ stand for "Structured Query Language".

	{SQL Standards (http://www.jcc.com/sql_stnd.html)}.

	{An SQL parser
	(ftp://ftp.ora.com/published/oreilly/nutshell/lexyacc/)} is
	described in "Lex & Yacc", by Levine, Mason & Brown published
	by O'Reilly.

	{The 1995 SQL Reunion: People, Projects, and Politics
	(http://www.mcjones.org/System_R/SQL_Reunion_95/)}.

	["A Guide to the SQL Standard", C.J. Date, A-W 1987].

	["SQL for Dummies", Allen G. Taylor, IDG Books Worldwide].

	(2005-11-17)

<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. <database, information science> A user's (or {agent}'s)
	request for information, generally as a formal request to a
	{database} or {search engine}.

	{SQL} is the most common {database query language}.

	2. <character> {question mark}.

	(1997-04-09)

<database> A collection of {records} in a {relational database}.

	(1997-06-04)

<memory management> /kash/ A small fast memory holding
	recently accessed data, designed to speed up subsequent access
	to the same data.  Most often applied to processor-memory
	access but also used for a local copy of data accessible over
	a network etc.

	When data is read from, or written to, {main memory} a copy is
	also saved in the cache, along with the associated main memory
	address.  The cache monitors addresses of subsequent reads to
	see if the required data is already in the cache.  If it is (a
	{cache hit}) then it is returned immediately and the main
	memory read is aborted (or not started).  If the data is not
	cached (a {cache miss}) then it is fetched from main memory
	and also saved in the cache.

	The cache is built from faster memory chips than main memory
	so a cache hit takes much less time to complete than a normal
	memory access.  The cache may be located on the same
	{integrated circuit} as the {CPU}, in order to further reduce
	the access time.  In this case it is often known as {primary
	cache} since there may be a larger, slower {secondary cache}
	outside the CPU chip.

	The most important characteristic of a cache is its {hit rate}
	- the fraction of all memory accesses which are satisfied from
	the cache.  This in turn depends on the cache design but
	mostly on its size relative to the main memory.  The size is
	limited by the cost of fast memory chips.

	The hit rate also depends on the access pattern of the
	particular program being run (the sequence of addresses being
	read and written).  Caches rely on two properties of the
	access patterns of most programs: temporal locality - if
	something is accessed once, it is likely to be accessed again
	soon, and spatial locality - if one memory location is
	accessed then nearby memory locations are also likely to be
	accessed.  In order to exploit spatial locality, caches often
	operate on several words at a time, a "{cache line}" or "cache
	block".  Main memory reads and writes are whole {cache lines}.

	When the processor wants to write to main memory, the data is
	first written to the cache on the assumption that the
	processor will probably read it again soon.  Various different
	policies are used.  In a {write-through} cache, data is
	written to main memory at the same time as it is cached.  In a
	{write-back} cache it is only written to main memory when it
	is forced out of the cache.

	If all accesses were writes then, with a write-through policy,
	every write to the cache would necessitate a main memory
	write, thus slowing the system down to main memory speed.
	However, statistically, most accesses are reads and most of
	these will be satisfied from the cache.  Write-through is
	simpler than write-back because an entry that is to be
	replaced can just be overwritten in the cache as it will
	already have been copied to main memory whereas write-back
	requires the cache to initiate a main memory write of the
	flushed entry followed (for a processor read) by a main memory
	read.  However, write-back is more efficient because an entry
	may be written many times in the cache without a main memory
	access.

	When the cache is full and it is desired to cache another line
	of data then a cache entry is selected to be written back to
	main memory or "flushed".  The new line is then put in its
	place.  Which entry is chosen to be flushed is determined by a
	"{replacement algorithm}".

	Some processors have separate instruction and data caches.
	Both can be active at the same time, allowing an instruction
	fetch to overlap with a data read or write.  This separation
	also avoids the possibility of bad {cache conflict} between
	say the instructions in a loop and some data in an array which
	is accessed by that loop.

	See also {direct mapped cache}, {fully associative cache},
	{sector mapping}, {set associative cache}.

	(1997-06-25)

<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)

<World-Wide Web, project> A {open source} {HTTP} server for
	{Unix}, {Windows NT}, and other {platforms}.  Apache was
	developed in early 1995, based on code and ideas found in the
	most popular HTTP server of the time, {NCSA httpd} 1.3.  It
	has since evolved to rival (and probably surpass) almost any
	other {Unix} based HTTP server in terms of functionality, and
	speed.  Since April 1996 Apache has been the most popular HTTP
	server on the {Internet}, in May 1999 it was running on 57% of
	all web servers.

	It features highly configurable error messages, {DBM}-based
	{authentication} {databases}, and {content negotiation}.

	Latest version: 1.3.9, as of 1999-10-27.

	{Home (http://www.apache.org/httpd.html)}.

	{FAQ (http://www.apache.org/docs/misc/FAQ.html)}.

	(1999-10-27)

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. 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. <programming> An {address}, from the point of view of a
	programming language.  A pointer may be typed, with its {type}
	indicating the type of data to which it points.

	The terms "pointer" and "reference" are generally
	interchangable although particular programming languages often
	differentiate these two in subtle ways.  For example, {Perl}
	always calls them references, never pointers.  Conversely, in
	C, "pointer" is used, although "a reference" is often used to
	denote the concept that a pointer implements.

	{Anthony Hoare} once said:

	Pointers are like jumps, leading wildly from one part of the
	data structure to another.  Their introduction into high-level
	languages has been a step backward from which we may never
	recover.

	[C.A.R.Hoare "Hints on Programming Language Design", 1973,
	Prentice-Hall collection of essays and papers by Tony Hoare].

	2. <operating system> (Or "mouse pointer") An {icon}, usually
	a small arrow, that moves on the screen in response to
	movement of a {pointing device}, typically a {mouse}.  The
	pointer shows the user which object on the screen will be
	selected etc. when a mouse button is clicked.

	(1999-07-07)

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)

<company> (IBM) The best known American computer manufacturer,
	founded by Thomas J. Watson (born 1874-02-17), known as "Big
	Blue" after the colour of its logo.  IBM makes everything from
	{mainframes} to {personal computers} (PCs) and has been
	immensely successful in selling them, chiefly to business.  It
	has often been said that "Nobody has ever been sacked for
	buying IBM".

	The {IBM PC} in its various versions has been so successful
	that unqualified reference to a "PC" almost certainly means a
	PC from IBM, or one of the many brands of {clone} produced by
	other manufacturers to cash in on IBM's original success.

	Alternative expansions of "IBM" such as Inferior But
	Marketable; It's Better Manually; Insidious Black Magic; It's
	Been Malfunctioning; Incontinent Bowel Movement, illustrate
	the considerable antipathy most hackers have long felt toward
	the "industry leader" (see {fear and loathing}).

	Quarterly sales $15351M, profits $689M (Aug 1994).

	{Home (http://www.ibm.com/)}.

	(1999-04-07)

A {relational DBMS} vendor.

<messaging> To request to receive messages posted to a
	{mailing list} or {newsgroup}.  In contrast to the mundane use
	of the word this is often free of charge.

	(1997-03-27)

[{Usenet}] 1. To duplicate a portion (or whole) of another's
	message (typically with attribution to the source) in a reply
	or followup, for clarifying the context of one's response.
	See the discussion of inclusion styles under "Hacker Writing
	Style".

	2. [{C}] "#include <disclaimer.h>" has appeared in {sig
	blocks} to refer to a notional "standard {disclaimer} file".

	[{Jargon File}]

1. To copy {data} (often {program} {code} to be {run}) into
	{memory}, possibly {parsing} it somehow in the process.
	E.g. "{WordPerfect} can't load this {RTF} file - are you sure
	it didn't get corrupted in the {download}?"  Opposite of
	{save}.

	2. The degree to which a computer, {network}, or other
	resource is used, sometimes expressed as a percentage of the
	maximum available.  E.g. "What kind of CPU load does that
	program give?", "The network's constantly running at 100%
	load".  Sometimes used, by extension, to mean "to increase the
	level of use of a resource".  E.g. "Loading a spreadsheet
	really loads the CPU".  See also: {load balancing}.

	3. To {install} a piece of {software} onto a system.
	E.g. "The computer guy is gonna come load Excel on my laptop
	for me".  This usage is widely considered to be incorrect.

	(2002-07-02)

<theory, programming> (Or "data type") A set of values from
	which a {variable}, {constant}, {function}, or other
	{expression} may take its value.  A type is a classification
	of data that tells the {compiler} or {interpreter} how the
	programmer intends to use it.  For example, the process and
	result of adding two variables differs greatly according to
	whether they are integers, floating point numbers, or strings.

	Types supported by most programming languages include
	{integers} (usually limited to some range so they will fit in
	one {word} of storage), {Booleans}, {floating point numbers},
	and characters.  {Strings} are also common, and are
	represented as {lists} of characters in some languages.

	If s and t are types, then so is s -> t, the type of
	{functions} from s to t; that is, give them a term of type s,
	functions of type s -> t will return a term of type t.

	Some types are {primitive} - built-in to the language, with no
	visible internal structure - e.g. Boolean; others are
	composite - constructed from one or more other types (of
	either kind) - e.g. {lists}, {arrays}, {structures}, {unions}.
	{Object-oriented programming} extends this with {classes}
	which encapsulate both the structure of a type and the
	operations that can be performed on it.

	Some languages provide {strong typing}, others allow {implicit
	type conversion} and/or {explicit type conversion}.

	(2003-12-22)