Agent
On the Internet, an agent (also called an intelligent agent) is a program that gathers information or performs some other service without your immediate presence and on some regular schedule. Typically, an agent program, using parameters you have provided, searches all or some part of the Internet, gathers information you’re interested in, and presents it to you on a daily or other periodic basis.
An example of an agent is Infogate, which alerts you about news on specified topics of interest. A number of similar agents compare shopping prices and bring the news back to the user. Other types of agents include specific site watchers that tell you when the site has been updated or look for other events and analyst agents that not only gather but organize and interpret information for you.
An agent is sometimes called a bot (short for robot). The practice or technology of having information brought to you by an agent is sometimes referred to as push technology.
aggregate
In general, to aggregate (verb, from Latin aggregate meaning to add to) is to collect things together. An aggregate (adjective) thing is a collection of other things. An aggregation is a collection.
In information technology, individual items of data are sometimes aggregated into a database. Unlike marshalling, aggregation doesn’t require giving one thing precedence over another thing.
aggregator
Like its synonym concentrator, an aggregator is any device that serves multiple other devices or users either with its own capabilities or by forwarding transmissions in a more concentrated and economical way. A remote access hub is sometimes referred to as an aggregator. A typical aggregator or remote access hub is a device that handles incoming dial-up calls for an Internet (or other network) POP and performs other services. An aggregator may be able to handle up to 100 dial-up modem calls, support a certain number of Integrated Services Digital Network connections, and support leased line and frame relay traffic while also functioning as a router.
aglet
1) In computer technology, an aglet (or ”agile applet”) is a small application program or applet with the capability to serve as a mobile agent of services in a computer network. An aglet has these characteristics:
• Object-passing capability. It is a complete program object with its own methods, data states, and travel itinerary that can send other aglets or pass itself along in a network as an entity.
• Autonomous. An aglet has the ability to decide on its own what actions to take and where and when to go elsewhere.
• Interaction with other program objects. It can interact locally with other aglets or stationary objects. When necessary, it can dispatch itself or other aglets to remote locations to interact with other objects there.
• Disconnected operation. If a computer is currently disconnected from the network, the aglet can schedule itself to move when the computer is reconnected.
• Parallel execution. Multiple aglets can be dispatched to run concurrently in different computers.
An aglet is a class or template in the Java object-oriented programming language and the mobile agent instances of its use are also called aglets.
Relatively simple examples of aglets are applications in which one aglet can dispatch another to a remote computer to display a note or to search for information and send it back or to notify a user on another computer that a page had changed. Much more complicated applications are envisioned (or are waiting to be envisioned).
The term apparently originated at IBM’s research laboratory in Japan. IBM offers a free Aglets Workbench, which is a visual programming environment for creating aglets. IBM has also created an application program interface, the Agent Transfer Protocol (ATP), for transferring agents between networked computers. Both the Agent Transfer Protocol and the Workbench framework protocol have been offered to the Object Management Group (OMG), an industry standards body, as a proposal for a standard Mobile Agent Facility. IBM is offering the Workbench free to developers.
2) An aglet is also the small plastic or fiber tube that binds the end of a shoelace (or similar cord) to prevent fraying and to allow the lace to be passed through an eyelet or other opening.
Al
AI (pronounced AYE-EYE) or artificial intelligence is the simulation of human intelligence processes by machines, especially computer systems. These processes include learning (the acquisition of information and rules for using the information), reasoning (using the rules to reach approximate or definite conclusions), and self-correction. Particular applications of AI include expert systems, speech recognition, and machine vision.
AlBO
AIBO (pronounced eye-bow) is an entertainment robot designed by Sony. AIBO means "companion" in Japanese. It is also an abbreviation for ”artificial intelligence bot” (”bot” is short for ”robot”) in English. Sony created AIBO to be a robotic pet and promotes AIBO as having the capability to interact with its human owner in many of the same ways a living pet would—without the high maintenance.
Sony classifies AIBO as an autonomous robot, meaning that it has the ability to learn, mature, and act on its own in response to external stimuli. AIBO has a brain (CPU), the ability to move (20 points of articulation), and sensory organs (sensors). AIBO’s developmental stages are controlled by a ”memory stick" application software. Human interaction with AIBO determines its ability to express its needs and emotions, as well as its ability to learn and mature. AIBO is capable of expressing happiness, sadness, anger, surprise, fear and dislike. Just like a pet that’s alive, the more interaction AIBO has with humans, the faster it learns.
AIBO’s head has a touch sensor for non-verbal communication, stereo microphones for hearing, a color video camera for vision, and a distance detector to allow AIBO to avoid obstacles. AIBO has voice recognition components that allow AIBO to be programmed to recognize its own name and understand over 50 verbal commands (depending on where AIBO is in its growth cycle). At present, AIBO is bi-lingual and understands Japanese and English; Sony plans to add German and French to increase the robot’s worldwide appeal. AIBO is able to communicate with humans by emitting musical tones and changing the color and shape of its eyes. AIBO can be ”taught” to play games, but unlike a game, AIBO cannot be reset. AIBO uses Sony’s OPEN-R platform to operate. OPEN-R is modular, so the robot’s hardware and software components can be easily changed. Sony plans to initiate a licensing program that will allow developers to use OPEN-R technology to create new applications for AIBO. They hope that opening up development will encourage the public’s acceptance of personal robots and help create a broad base of consumers interested in purchasing entertainment or household-helper robots. SONY has released two models of AIBO. The first version of AIBO resembled a dog. The second version of AIBO is said to be modeled after a lion cub. The basic AIBO model sells in the United States for $1,500. The deluxe version, which comes with a charging station, carrying bag, extra battery and additional software package sells for $2,800.
AlFF
AIFF (Audio Interchange File Format) is one of the two most-used audio file formats used in the Apple Macintosh operating system. The other is Sound Designer II (SDII). Most CD writers can accept AIFF or SDII files interchangeably when writing a Red Book audio CD. AIFF is sometimes referred to as ”Apple Interchange File Format.”
The extension for this file type is ”.aif” when it is used on a PC. On a Mac, the file extension is not needed. A Mac file uses a Type and Creator resource to identify itself to the operating system and the applications that can open it.
An AIFF file contains the raw audio data, channel information (monophonic or stereophonic), bit depth, sample rate, and application-specific data areas. The application-specific data areas let different applications add information to the file header that remains there even if the file is opened and processed by another application. For example, a file could retain information about selected regions of the audio data used for recalling zoom levels not used by other applications.
air interface
In cellular telephone communications, the air interface is the radio-frequency portion of the circuit between the cellular phone set or wireless modem (usually portable or mobile) and the active base station. As a subscriber moves from one cell to another in the system, the active base station changes periodically. Each changeover is known as a handoff.
A cellular connection is only as good as its weakest link, which is almost always the air interface. Radio-frequency (RF) circuits are subject to many variables that affect signal quality. Factors that can cause problems include:
• Use of the handheld phone set or portable wireless modem inside buildings, cars, buses, trucks, or trains
• Proximity to human-made, steel-frame obstructions, especially large buildings and freeway overpasses
• Abundance of utility wires that can reflect radio signals and/or generate noise that interferes with reception
• Irregular terrain, particularly canyons and ravines
• Inadequate transmitter power in phone set or wireless modem
• Poorly designed antenna in phone set or wireless modem
In addition to these variables, some cellular networks have inadequate coverage in certain geographic areas. Usually this is because there are not enough base stations to ensure continuous communications for subscribers using portable (handheld) phone sets. As a network evolves, more base stations may be installed in a given region, and in that case, this problem will diminish with time. Conversion of a network from analog to digital can result in dramatic improvement.
AIX
AIX is an open operating system from IBM that is based on a version of UNIX. AIX/ESA was designed for IBM’s System/ 390 or large server hardware platform. AIX/6000 is an operating system that runs on IBM’s workstation platform, the RISC System/6000.
algebraic number
An algebraic number is any real number that is a solution of some single-variable polynomial equation whose coefficients are all integers. While this is an abstract notion, theoretical mathematics has potentially far-reaching applications in communications and computer science, especially in data encryption and security. The general form of a single-variable polynomial equation is:
where a0, a1, a2, …, an are the coefficients, and x is the unknown for which the equation is to be solved. A number x is algebraic if and only if there exists some equation of the above form such that a0, aj, a2, …, an are all integers.
All rational numbers are algebraic. Examples include 25, 7/9, and -0.245245245. Some irrational numbers are also algebraic. Examples are 21/2 (the square root of 2) and 31/3 (the cube root of 3). There are irrational numbers x for which no single-variable, integer-coefficient polynomial equation exists with x as a solution. Examples are pi (the ratio of a circle’s circumference to its diameter in a plane) and e (the natural logarithm base). Numbers of this type are known as transcendental numbers.
algorithm
The term algorithm (pronounced AL-go-rith-um) is a procedure or formula for solving a problem. The word derives from the name of the mathematician, Mohammed ibn-Musa Al-Khowarizmi, who was part of the royal court in Baghdad and who lived from about 780 to 850. Al-Khowarizmi’s work is the likely source for the word algebra as well.
A computer program can be viewed as an elaborate algorithm. In mathematics and computer science, an algorithm usually means a small procedure that solves a recurrent problem.
alias
In general, as a noun, an alias (pronounced AY-lee-uhs) is an alternate name for someone or something. In literature, a ”pen name” is an alias for the author’s real name. The noun is derived from the Latin adverb alias, meaning ”otherwise” and by extension ”otherwise known as” and the latter meaning is still used in English, as in: Clark Kent, alias Superman. In information technology, the noun has at least two different usages.
1) In some computer operating systems and programming languages, an alias is an alternative and usually easier-to-understand or more significant name for a defined data object. The data object can be defined once and later a programmer can define one or more equivalent aliases that will also refer to the data object. In some languages, this is known as an ”equate” instruction.
2) In Macintosh operating systems, an alias is a desktop icon for a particular program or data object.
aliasing
In sound and image generation, aliasing is the generation of a false (alias) frequency along with the correct one when doing frequency sampling. For images, this produces a jagged edge, or stair-step effect. For sound, it produces a buzz.
Aloha
Aloha, also called the Aloha method, refers to a simple communications scheme in which each source (transmitter) in a network sends data whenever there is a frame to send. If the frame successfully reaches the destination (receiver), the next frame is sent. If the frame fails to be received at the destination, it is sent again. This protocol was originally developed at the University of Hawaii for use with satellite communication systems in the Pacific.
In a wireless broadcast system or a half-duplex two-way link, Aloha works perfectly. But as networks become more complex, for example in an Ethernet system involving multiple sources and destinations that share a common data path, trouble occurs because data frames collide (conflict). The heavier the communications volume, the worse the collision problems become. The result is degradation of system efficiency, because when two frames collide, the data contained in both frames is lost.
To minimize the number of collisions, thereby optimizing network efficiency and increasing the number of subscribers that can use a given network, a scheme called slotted Aloha was developed. This system employs signals called beacons that are sent at precise intervals and tell each source when the channel is clear to send a frame. Further improvement can be realized by a more sophisticated protocol called Carrier Sense Multiple Access with Collision Detection (CSMA/CD).
Alpha
Alpha is both a microprocessor and the name of a computer system from the Digital Equipment Corporation (DEC), which is now part of Compaq. The Alpha processor uses a newer and more advanced architecture than DEC’s flagship computer line, the VAX. The Alpha is based on reduced instruction set computer (reduced instruction set computing) architecture and handles 64 bits at a time. DEC has added its own refinements to the RISC architecture to further increase performance.
The latest models of DEC’s Alpha computer systems are offered with either DEC’s UNIX operating system or with Windows NT. (DECUS states that DEC’s OpenVMS also runs on Alpha computers.) DEC offers its AlphaServer together with a packaged solution with Digital’s AltaVista search engine for indexing and searching data within an enterprise’s intranet. Its AlphaStation line offers personal workstations in the $4-8,000 range.
AltaVista
AltaVista is a popular search engine on the Web. In addition to full-text searches, AltaVista can also search graphic images and tell you who is linked to your own Web pages. AltaVista’s search robot, known as Scooter, can look at and collect data from three million Web pages per day. Its indexer, Ni2, indexes one gigabyte of data per hour.
alternate newsgroup
”alt.” is the prefix for any of the hundreds of ”alternate” user-originated newsgroups that are part of Usenet. Like other newsgroups, each ”alt.” newsgroup is arranged in a hierarchy of topical discussion boards that you may read or post to. ”alt” is one of many major newsgroups; others include: news, rec (recreation), comp (computers), and soc (social). The ”alt” newsgroups are known (and used most frequently) for their alt.sex and related categories, but are also known for including a wide and inventive range of discussion topics.
The easiest way to get access to newsgroups is through the Google Web site.
alternating current
Also see current, voltage, and direct current.
In electricity, alternating current (AC) occurs when charge carriers in a conductor or semiconductor periodically reverse their direction of movement. Household utility current in most countries is AC with a frequency of 60 hertz (60 complete cycles per second), although in some countries it is 50 Hz. The radio-frequency (RF) current in antennas and transmission lines is another example of AC.
An AC waveform can be sinusoidal, square, or sawtooth-shaped. Some AC waveforms are irregular or complicated. An example of sine-wave AC is common household utility current (in the ideal case). Square or sawtooth waves are produced by certain types of electronic oscillators, and by a low-end uninterruptible power supply (UPS) when it is operating from its battery. Irregular AC waves are produced by audio amplifiers that deal with analog voice signals and/ or music.
The voltage of an AC power source can be easily changed by means of a power transformer. This allows the voltage to be stepped up (increased) for transmission and distribution.
High-voltage transmission is more efficient than low-voltage transmission over long distances, because the loss caused by conductor resistance decreases as the voltage increases. The voltage of an AC power source changes from instant to instant in time. The effective voltage of an AC utility power source is usually considered to be the DC voltage that would produce the same power dissipation as heat assuming a pure resistance. The effective voltage for a sine wave is not the same as the peak voltage. To obtain effective voltage from peak voltage, multiply by 0.707. To obtain peak voltage from effective voltage, multiply by 1.414. For example, if an AC power source has an effective voltage of 117 V, typical of a household in the United States, the peak voltage is 165 V.
Amateur radio
Amateur radio, also known as ham radio, is a hobby enjoyed by several hundred thousand people in the United States and by over a million people worldwide. Amateur radio operators call themselves ”radio hams” or simply ”hams.”
To become a radio ham, you must pass an examination. Wireless amateur communication is done on numerous bands (relatively narrow frequency segments) extending from 1.8 MHz (a wavelength of about 160 meters) upwards through several hundred gigahertz (wavelengths in the millimeter range). There are several license classes. The more privileges a class of license conveys, the more difficult is the examination that one must pass to obtain it.
Amateur radio operation is fun, and that is one of the main reasons hams do it. But ham radio can provide communication during states of emergency. Ham radio works when all other services fail. After Hurricane Andrew struck South Florida in 1992, the utility grid was destroyed over hundreds of square miles. All cellular towers and antennas were blown down. Only amateur radio, the Citizens Radio Service (”Citizens Band”), and a few isolated pay phones with underground lines provided communication between the outside world and the public in the affected area.
Amateur radio operators are known as technical innovators, and have been responsible for important discoveries. For example, in the early part of the 20th century, government officials believed that all the frequencies having wavelengths shorter than 200 meters (1.5 MHz) were useless for radio communications, so they restricted radio amateurs to these frequencies. It was not long before ham radio operators discovered the truth, and were communicating on a worldwide scale using low-power transmitters. Thus the shortwave radio era began.
