A
disc jockey (also known as
DJ
or
deejay) is a person who selects and plays
recorded music for an audience.
Originally, dis
k referred to
phonograph records, while dis
c referred to
the
Compact Disc, and has become the
more common spelling. Today, the term includes all forms of music
playback, no matter the source.
There are several types of disc jockeys. Radio DJs introduce and
play music that is broadcast on
AM,
FM,
shortwave,
digital,
or
internet radio stations. Club DJs
select and play music in
bars,
nightclubs,
discothèques, at
raves,
or even in a
stadium.
Hip
hop disc jockeys select and play music using multiple
turntable, often to back up one or more
MC, and they may also do turntable
scratching to create percussive sounds. In
reggae, the disc jockey (
deejay) is a vocalist who
raps, "
toasts", or chats
over pre-recorded rhythm tracks while the individual choosing and
playing them is referred to as a
selector. Mobile disc jockeys travel
with portable sound systems and play recorded music at a variety of
events.
Equipment and techniques
djDJ equipment may consist of:
- Sound recordings in a DJ's preferred medium (e.g., vinyl records, Compact Discs, computer media
files, etc.);
- A combination of two devices (or only one, if playback is
digital) to play sound recordings, for alternating back and forth
to create a continuous playback of music (e.g., record players,
Compact Disc players, computer media players such as an MP3 player, etc.);
- A sound system for amplification or
broadcasting of the recordings (e.g., portable audio system,
PA system) or a radio broadcasting
system;
- A DJ mixer, which is an electronic
(usually 2- or 4-channel) audio mixer
usually equipped with a crossfader used to smoothly go from
one song to another, using two or more playback devices;
- Headphones, used to listen to one
recording while the other recording is being played to the
audience; and
- Optionally, a microphone, so that the
DJ can introduce songs and speak to the audience.
Other equipment could or can be added to the basic DJ setup
(above), providing unique sound manipulations. Such devices
include, but are not limited to:
- Electronic effects units (delay, reverb,
octave, equalizer, chorus,
etc.). Some club DJs use a sub-harmonic synthesizer effect which
either doubles low frequencies with energy added an octave lower or
synthesizes harmonics such that the impression of a very low bass
sound is added to the mix.
- A computerised performance system, which can be used with
vinyl emulation software to
manipulate digital files on the computer in real time.
- Multi-stylus headshells, which allow a DJ to play different
grooves of the same record at the same time.
- Special DJ digital
controller hardware can manipulate digital files on a PC or
laptop;
- Sampler,
sequencers, electronic musical keyboards (synthesizers), or
drum machines.
Several techniques are used by DJs as a means to better mix and
blend recorded music. These techniques primarily include the
cuing,
equalization, and
audio mixing of two or more
sound sources. The complexity and frequency of special techniques
depends largely on the setting in which a DJ is working. Radio DJs
are less likely to focus on music-mixing procedures than club DJs,
who rely on a smooth transition between songs using a range of
techniques.
Club DJ turntable techniques include
beatmatching,
phrasing, and
slip-cueing to preserve energy on a dancefloor.
Turntablism embodies the art of
cutting,
beat
juggling,
scratching,
needle drop,
phase shifting,
back
spinning, and more to perform the transitions and overdubs of
samples in a more creative manner
(although turntablism is often considered a use of the turntable as
a
musical instrument rather than
a tool for blending recorded music). Professional DJs may use
harmonic mixing to choose songs that
are in compatible musical keys.
Types
The role of selecting and playing
recorded music for an intended audience is
the same for every disc jockey. The selected music, the audience,
the setting, the preferred medium, and the level of sophistication
of sound manipulation are factors that differentiate the various DJ
types.
Radio
A radio disc jockey plays music that is broadcast across radio
waves—AM and FM bands, or worldwide on shortwave radio stations.
Radio DJs are often known for their personalities.
Famous American radio disc jockeys such as
Alan Freed,
Scott Muni,
Casey Kasem,
Dick
Biondi,
Wolfman Jack, and
Dr. Demento built their audiences using a
combination of the nature of the songs they selected and strong
on-air personalities. A modern-day
commercial radio disc jockey will
typically rely on his or her on-air character alone, as the
station's playlist has been predetermined by a program director or
music director.
Radio disc jockeys appear in a wide array of
broadcast formats, from
top
40 or
contemporary hit
radio (CHR) to
oldies and other formats
that are defined by the type of songs played. Formats are defined
by the type of originating station, with
public radio,
college
radio, and
pirate radio as
examples. Some national governments operate official radio stations
for a global audience, such as
Voice of
America (hosted by the United States) and
Voice of Russia (organized by the Russian
government). These stations may include programs by disc jockeys;
The Clash frontman
Joe Strummer played selections from his musical
library for the UK's
BBC World
Service in the 1990s. Large military units sometimes broadcast
their own radio programs to their troops, inserting news, weather
reports, and advice between popular songs. The film
Good Morning, Vietnam portrays an
American military disc jockey.
Reggae
In Jamaican
reggae music, the Disc Jockey,
called the "Selector", controls the tone, vibe, and energy of a
dance or gathering. As Norman Stolzoff notes in "Wake the Town And
Tell the People", The crowd's reception of the selector ultimately
"determined the success or failure of a sound system's
performance". A careful combination of songs in a playlist were
often used to tell stories, set moods for the party goers, or to
convey a particular theme. A selector had to know how to adapt the
tempo, musical key, and tone of the songs he or she selected.
Selectors would often tease the crowd with small snippets from
individual songs throughout an entire dance only to play the full
song near the end of the dance. Another technique known as the
"haul and pull up" called for the selector to interrupt a classic
by restarting the song in the middle of playing by literally
lifting up the needle and returning the beginning of the record.
These skills are in addition to the precise timing required of a
selector in switching records between songs or when the crowd
disapproved of a particular song by verbally expressing their
frustration.
The selector also interacted with and pleased the crowd throughout
the entire dance by any means necessary. Over time, specific styles
emerged amongst selectors that used witty voice overs and "toasts"
to complement their performance. Count Matchukie( Winston Cooper),
one of Jamaica's most famed selectors, would do dancing and talking
over records with humor and wit. "Cliff" of Duke Reid's sound
system focused so intensely on his task that he would turn his back
to the crowd and would never speak at all as he played. Adding an
even greater degree of complexity to the job of a selector,
"toasting" required wit, humor, and a specific usage of rhyme,
timing, and rhythm. Nonetheless, in both the eras of sound system
dances and in dancehall, the selector was often the greatest
selling point of a specific dance, party or system.
Clubs
A club disc jockey selects and plays music using several
turntables, CD players, or a hard-drive source, mixing the songs
with a mixer and modifying the tone or sound of the recordings with
equalizers and other effects. The setting can range anywhere from a
neighborhood party at a private home or a small nightclub to a
discothèque, a rave, or even a stadium. The size of the sound
system varies according to the venue, and can range from a 500 watt
PA system with two small speakers at a
house party to a 50,000 watt
sound reinforcement system with a
number of speakers and multiple 15"
subwoofers at a major dance club. The main focus
of club DJs is on the music they play and how they mix tracks in
and out, sometimes just to add a bit of energy to a track. They
build their
set by choosing "tracks" (songs)
to control the energy level of the crowd and use
beatmixing and beatmatching techniques to make
seamless transitions between tracks. Some DJs may interweave a
number of different songs or samples into each track that they
play. For more information on notable club DJs, see
List of club DJs.
A DJ cues up a track with his headphones.
Hip-hop
A
hip-hop disc jockey is a DJ that selects
and plays music as a hip-hop artist and/or performer, often backing
up one or more
MC.
Mobile disc jockeys

A mobile DJ.
Mobile disc jockeys are an
extension of the original
radio disc jockeys.
They travel with or go on tour with mobile sound systems and play
from an extensive collection of recorded content for a specific
audience. Today, mobile DJs need a large selection of music,
professional-grade equipment, good organizational skills, vocal
talent as an
MC, mixing skills, quality lighting,
insurance for liability, and on-site backup equipment. In the
2000s, the role of the mobile DJ has expanded. Many mobile DJs have
assumed additional responsibilities to ensure an event's success.
These responsibilities include the roles of MC, event organizer and
coordinator, lighting director, and/or sound engineer.
In the past, Mobile DJs utilized vinyl records or cassettes. During
the
disco era of the 1970s, demand for mobile
DJs (called "mobile discos" in the UK) soared, and top disc jockeys
travelled with hundreds of vinyl records and
cassette tapes. In the 1990s, Compact Discs
became the standard.
Mobile disc
jockey trade publications such as
DJ
Times magazine and
Mobile
Beat were founded in this era. Mobile DJs have formed
professional associations such as the Canadian Disc Jockey
Association (CDJA), the Canadian Online Disc Jockey Association
(CODJA), the American Disc Jockey Association (ADJA), and the
National Association of Mobile Entertainers. In the UK,
associations include the National Association of Disc Jockeys
(NADJ), the South Eastern Discothèque Association (SEDA), the
Mobile DJ Network In the 2000s, many mobile DJs rely heavily on
laptop computers and MP3s for sequencing and mixing. This
technology allows DJs to do mixing prior to an event and also
lightens the load by reducing the number of CDs that a DJ must
carry to an event.
History
19th century to 1920s
In 1857,
Leon Scott invented the phonoautograph in France
, the first
device to record sound. In 1877, Charles
Cros invented the phonograph in France (it was patented before
Edison's invention but never built) and Thomas Alva Edison invented the phonograph cylinder, the first device to
play back recorded sound, in the United States
. In 1892,
Emile
Berliner began commercial production of his gramophone records,
the first disc records to be offered to the public. In 1906,
Reginald Fessenden transmitted
the first audio radio
broadcast in
history also playing the first record, that of a
contralto singing
Handel's Largo from
Xerxes.
The world's first radio disc jockey was Ray Newby, of Stockton,
California. In 1909, at 16 years of age, Newby began regularly
playing records on a small
spark
transmitter while a student at Herrold College of Engineering
and Wireless, located in San Jose, California, under the authority
of radio pioneer
Charles "Doc"
Herrold.
By 1910, regular radio broadcasting had started to use "live" as
well as prerecorded sound. In the early radio age, content
typically included comedy, drama, news, music, and sports
reporting. The on-air announcers and programmers would later be
known as disc jockeys. In the 1920s,
juke
joints became popular as places for dancing and drinking to
recorded jukebox music.
In 1927, Christopher Stone became the
first radio announcer and programmer in the United Kingdom
, on the BBC radio
station. In 1929, Thomas Edison ceased phonograph cylinder
manufacture, ending the disc and cylinder rivalry.
1930s–1950s
In 1935, American commentator
Walter
Winchell coined the term "disc jockey" (the combination of
"disc" (referring to the disc records) and "jockey" (which is an
operator of a machine) as a description of radio announcer
Martin Block, the first announcer to become a
star.
While his audience was awaiting developments
in the Lindbergh
kidnapping
, Block played records and created the illusion that
he was broadcasting from a ballroom, with the nation’s top dance
bands performing live. The show, which he called
Make
Believe Ballroom, was an instant hit. The term "disc jockey"
appeared in print in
Variety in 1941.
In 1943,
Jimmy Savile launched the world's first
DJ dance party by playing jazz records in the
upstairs function room of the Loyal Order of Ancient Shepherds in
Otley
, England
. In
1947, he became the first DJ to use twin turntables for continuous
play.
Also
in 1947, the Whiskey à Go-Go nightclub opened in Paris, France
, considered to be the world's first discothèque, or
disco (deriving its name from the French word meaning a nightclub
where the featured entertainment is recorded music rather than an
on-stage band). Discos began appearing across Europe and the
United States. From the late 1940s to early 1950s, the introduction
of television eroded the popularity of radio's early format,
causing it to take on the general form it has today, with a strong
focus on music, news, and sports.
In the 1950s, American radio DJs would appear live at "sock hops"
and "platter parties" and assume the role of a human jukebox. They
would usually play 45-rpm records, featuring hit singles on one
turntable while talking between songs. In some cases, a live
drummer was hired to play beats between songs to maintain the dance
floor. In 1955,
Bob Casey, a
well-known "sock hop" DJ, brought the two-turntable system to the
U.S. Throughout the 1950s,
payola payments by
record companies to DJs in return for airplay were an ongoing
problem. Part of the fallout from the payola scandal was tighter
control of the music by station management. The
Top 40 format emerged, where popular songs are played
repeatedly.
In the
late 1950s, sound system, a new
form of public entertainment, were developed in the ghettos of Kingston, Jamaica
. Promoters, who called themselves DJs, would
throw large parties in the streets that centered on the disc
jockey, called the "selector," who played dance music from large,
loud
PA systems and bantered over the
music with a boastful, rhythmic chanting style called "
toasting." These parties quickly became profitable
for the promoters, who would sell admission, food, and alcohol,
leading to fierce competition between DJs for the biggest sound
systems and newest records.
1960s and 1970s

200 px
In the mid-1960s, nightclubs and discothèques continued to grow in
Europe and the United States. Specialized DJ equipment, such as
Rudy Bozak's classic CMA-10-2DL mixer,
began to appear on the market.
In 1969, American club DJ Francis Grasso popularized beatmatching at
New
York
's Sanctuary nightclub. Beatmatching is the
technique of creating seamless transitions between records with
matching beats, or tempos. Grasso also developed
slip-cuing, the technique of holding a
record still while the turntable is revolving underneath, releasing
it at the desired moment to create a sudden transition from the
previous record.
By 1968, the number of dance clubs started to decline; most
American clubs either closed or were transformed into clubs
featuring live bands.
Neighborhood block parties that were modelled
after Jamaican sound systems gained popularity in Europe and in the
boroughs of New York City
.
In 1973,
Jamaican-born
DJ Kool Herc, widely
regarded as the "godfather of hip-hop culture," performed at block
parties in his Bronx
neighborhood
and developed a technique of mixing back and forth between two
identical records to extend the rhythmic instrumental segment, or
break. Turntablism,
the art of using turntables not only to play music but to
manipulate sound and create original music, began to develop.
In 1974,
Technics released the
first
SL-1200 turntable, which
evolved into the SL-1200 MK2 in 1979—which, as of the mid-2000s,
remains the industry standard for deejaying. In 1974, German
electronic music band
Kraftwerk released the 22-minute song "Autobahn,"
which takes up the entire first side of that LP. Years later,
Kraftwerk would become a significant influence on
hip-hop artists such as
Afrika Bambaataa and
house music pioneer
Frankie Knuckles. During the mid-1970s,
Hip-hop music and culture began to
emerge, originating among urban
African
Americans and
Latinos in New York City.
The four main elements of
hip-hop culture
were
MCing , DJing,
graffiti, and
breakdancing.
In the
mid-1970s, the soul-funk blend of dance pop known as disco took off
in the mainstream pop charts in the United States
and Europe, causing discothèques to experience a
rebirth. Unlike many late-1960s clubs, which featured live
bands, discothèques used the DJ's selection and mixing of records
as the entertainment. In 1975,
record
pools began, providing disc jockeys access to newer music from
the industry in an efficient method.
In 1975, hip-hop DJ
Grand Wizard
Theodore invented the scratching technique by accident. In
1976, American DJ, editor, and producer
Walter Gibbons remixed "Ten Percent" by
Double Exposure, one of the
earliest commercially released 12″ singles (aka "maxi-single"). In
1979, the
Sugar Hill Gang released
"
Rapper's Delight," the first
hip-hop record to become a hit. It was also the first real
breakthrough for
sampling, as the
bassline of
Chic's "
Good Times" laid the foundation for
the song.
In 1977,
Saratoga
Springs, NY
disc jockey Tom L. Lewis introduced the
Disco Bible (later renamed Disco Beats), which published hit disco
songs listed by beats per minute (tempo), as well as by either
artist or song title. Billboard ran an article on the new
publication, and it went national relatively quickly. The list made
it easier for beginning DJs to learn how to create seamless
transitions between songs without dancers having to change their
rhythm on the dance floor. Today, DJs can find the beats per minute
of songs in the BPM List.
1980s
In 1981, the cable television network
MTV was
launched, originally devoted to music videos, especially popular
rock music. The term "
video jockey," or
VJ, was used to describe the fresh-faced youth who introduced the
music videos. In 1982, the demise of disco in the mainstream by the
summer of 1982 forced many nightclubs to either close or change
entertainment styles, such as by providing MTV-style video dancing
or live bands. Released in 1982, the song "Planet Rock" by DJ
Afrika Bambaataa was the first
hip-hop song to feature
synthesizers.
The song melded electronic hip-hop beats with the melody from
Kraftwerk's "Trans-Europe Express." In 1982, the Compact Disc
reached the public market in Asia, and early the following year in
other markets. This event is often seen as the "Big Bang" of the
digital audio revolution.
In the early 1980s, NYC disco DJ
Larry
Levan, known for his eclectic mixes, gained a cult following,
and the
Paradise Garage, the
nightclub at which he spun, became the prototype for the modern
dance club where the music and the DJ were showcased. Around the
same time, the disco-influenced electronic style of dance music
called
house music emerged in Chicago.
The name
was derived from the Warehouse Club
in Chicago
, where resident DJ Frankie Knuckles mixed old disco classics
and Eurosynth pop. House music is essentially disco music
with electronic drum machine beats. The common element of most
house music is a 4/4 beat generated by a
drum machine or other electronic means (such as
a sampler), together with a solid (usually also electronically
generated) synth
bassline. In 1983,
Jesse Saunders released what some
consider the first house music track, "On & On." The mid-1980s
also saw the emergence of
New York
Garage, a house music hybrid that was inspired by Levan's style
and sometimes eschewed the accentuated high-hats of the
Chicago house sound.
During
the mid-1980s, techno music emerged
from the Detroit
club scene. Being geographically located
between Chicago and New York, Detroit techno artists combined
elements of Chicago house and New York garage along with European
imports. Techno distanced itself from disco's roots by becoming
almost purely electronic with synthesized beats.
In 1985, the Winter
Music Conference started in Fort Lauderdale
Florida and became the premier electronic music
conference for dance music disc jockeys.
In 1985, TRAX Dance Music Guide was launched by
American Record Pool in Beverly Hills.
It was the first national DJ-published music magazine, created on
the
Macintosh computer using extensive
music market research and early desktop publishing tools. In 1986,
"
Walk This Way," a rap/rock
collaboration by
Run DMC and
Aerosmith, became the first hip-hop song to reach
the Top 10 on the
Billboard Hot
100. This song was the first exposure of hip-hop music, as well
as the concept of the disc jockey as band member and artist, to
many mainstream audiences. In 1988,
DJ Times magazine was
first published. It was the first US-based magazine specifically
geared toward the professional mobile and club DJ.
Starting in the mid-1980s, the wedding and banquet business changed
dramatically with the introduction of DJ music, replacing the bands
that had been the norm. Bandleaders, like Jerry Perell and others,
started DJ companies, such as NY Rhythm DJ Entertainers. Using
their knowledge of audience participation, MC charisma, and
"crowd-pleasing" repertory selection, the wedding music industry
became almost all DJ while combining the class and elegance of the
traditional band presentation. New DJs as well as bandleaders with
years of experience and professionalism transformed the entire
industry.
1990s
During the early 1990s, the rave scene built on the
acid house scene. The rave scene changed dance
music, the image of DJs, and the nature of promoting. The
innovative marketing surrounding the rave scene created the first
superstar DJs who established marketable
"brands" around their names and sound. Some of these celebrity DJs
toured around the world and were able to branch out into other
music-related activities. During the early 1990s, the Compact Disc
surpassed the gramophone record in popularity, but gramophone
records continued to be made (although in very limited quantities)
into the 21st century—particularly for club DJs and for local acts
recording on small regional labels. During the mid-1990s,
trance music, having run rampant in the German
underground for several years, emerged as a major force in dance
music throughout Europe and the UK. It became one of the world's
most dominant forms dance music by the end of the 1990s, thanks to
a trend away from its repetitive, hypnotic roots, and towards
commercialized song structure.
In 1991,
Mobile Beat magazine, geared specifically toward
mobile DJs, began publishing. In 1992,
MPEG
which stands for the
Moving
Picture Experts Group, released The MPEG-1 standard, designed
to produce reasonable sound at low bit rates. The lossy compression
scheme MPEG-1 Layer-3, popularly known as
MP3,
later revolutionized the digital music domain. In 1993, the first
internet "radio station", Internet Talk
Radio, was developed by
Carl Malamud.
Because the audio was relayed over the internet, it was possible to
access internet radio stations from anywhere in the world. This
made it a popular service for both amateur and professional disc
jockeys operating from a personal computer.
In 1995, the first full-time, internet-only radio station, Radio
HK, began broadcasting the music of
independent bands. In 1996, Mobile Beat
had its first national mobile DJ convention in Las Vegas. During
the late 1990s,
nu metal bands, such as
Korn,
Limp Bizkit,
and
Linkin Park, reached the height of
their popularity. This new subgenre of
alternative rock bore some influence from
hip-hop because rhythmic innovation and syncopation are primary,
often featuring DJs as band members. As well, during the late
1990s, various DJ and VJ software programs were developed, allowing
personal computer users to deejay or veejay using his or her
personal music or video files.
In 1998, the first MP3 digital audio player was released, the Eiger
Labs MPMan F10.
Final Scratch debuted
at the BE Developer Conference, marking the first digital DJ system
to allow DJs control of MP3 files through special
time coded vinyl records or CDs.
While it would take sometime for this novel concept to catch on
with the "die hard Vinyl DJs", This would soon become the first
step in the new Digital DJ revolution. Manufacturers joined with
computer DJing pioneers to offer
professional endorsements, the first being Professor Jam, who went
on to develop the industry's first dedicated computer DJ convention
and learning program, the "CPS (Computerized Performance System) DJ
Summit", to help spread the word about the advantages of this
emerging technology.
In 1999,
Shawn Fanning released
Napster, the first of the massively popular
peer-to-peer file sharing systems. During this period, the
AVLA (Audio Video Licensing Agency) of Canada announced an MP3
DJing license, administered by the Canadian Recording Industry
Association. This meant that DJs could apply for a license giving
them the right to perform publicly using music stored on a hard
drive, instead of having to cart their whole CD collections around
to their gigs.
2000s
By the 2000s, new technologies such as
voice tracking, allowed single DJs to send
announcements across many stations. Commercial radio DJs were
increasingly limited in their freedom to select which songs to
play. Some music aficionados sought
freeform stations that put the DJs
back in control, or chose instead to listen to
satellite radio services or portable music
players.
College radio stations and
other
public radio outlets continued to
be the most common places for freeform play lists in the U.S.
In the late 1990s and early 2000s, the convenience and popularity
of the MP3 and the increasing power of laptops spawned a new type
of DJ, the "MP3J". In 2004 Serato introduced its own version of the
digital vinyl DJ system
Serato
Scratch Live making improvements in overall system stability
and more closely emulating the feel of true vinyl.
Rane has since licensed the software as well as
collaborated with Serato to bring out a hardware mixer version in
2006. Soon afterward, many nightclub deejays that had remained true
vinyl record aficionados began the transition to becoming digital
vinyl users. Serato Scratch Live has since become the most popular
MP3 manipulation software/hardware, and can be found pre-installed
in famous clubs around the world. In 2006, the concept of DJ had
its 100-year anniversary. In January 2008, Serato introduced
Video-SL, which is a plug-in for the popular Serato Scratch Live
software. This plug-in gives DJs the ability to manipulate music
videos in the same way they have been manipulating music, spawning
a new generation of "VJs" (Video Jockeys).
In the late 2000s,
topless female DJs have appeared in special nightclubs, primarily
in Finland
and Russia
.
See also
Notes
References
- Assef, Claudia (2000). Todo DJ Já Sambou: A História do
Disc-Jóquei no Brasil. São Paulo: Conrad Editora do Brasil.
ISBN 85-87193-94-5.
- Brewster, Bill, and Frank Broughton (2000). Last Night a DJ
Saved My Life: The History of the Disc Jockey. New York: Grove
Press. ISBN 0-8021-3688-5 (North American edition). London:
Headline. ISBN 0-7472-6230-6 (UK edition).
- Broughton, Frank, and Bill Brewster. How to DJ Right: The
Art and Science of Playing Records. New York: Grove Press,
2003.
- Graudins, Charles A. How to Be a DJ. Boston: Course
Technology PTR, 2004.
- Lawrence, Tim (2004). Love Saves the Day: A History of
American Dance Music Culture, 1970–1979 . Duke University
Press. ISBN 0-8223-3198-5.
- Miller, Paul D. aka DJ Spooky, Sound Unbound: Writings on
DJ Culture and Electronic Music, MIT Press 2008. ISBN
0-2626-3363-9 ISBN 978-0-2626-3363-5.
- Poschardt, Ulf (1998). DJ Culture. London: Quartet
Books. ISBN 0-7043-8098-6.
- Zemon, Stacy. The Mobile DJ Handbook: How to Start &
Run a Profitable Mobile Disc Jockey Service, Second Edition.
St. Louis: Focal Press, 2002.
External links