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vacuum column:
In a magnetic tape drive, a cavity in which a lower air pressure is maintained so as to attract a tape loop between the spool and the driving mechanism.

validation test:
A test to determine whether an implemented system fulfills its specified requirements.

Synonym for valuator device.

valuator device:
An input unit that provides a scalar value; for example: a thumbwheel, a potentiometer, a control dial, a scroll bar. Synonymous with valuator.

A selected element from a specified domain of definition.

value-added network (VAN):
A network that provides additional services such as alternate routing and uninterruptable power supply.

value-added network.

(1) A named instance of a data type. (2) A quadruple, established by a declaration or an implicit declaration, that consists of an identifier, a set of data attributes, one or more addresses, and data values, where the relationship between the addresses and the data values may vary. In some programming languages, the addresses may vary, hence the associated data values may vary. In other programming languages, the addresses remain fixed, but the associated data values may change during execution.

variable function generator:
A function generator in which the function it generates may be set by the user before or during computation.

variable-point representation system:
A radix notation in which the radix point is explicitly indicated by a special character at that position.

variable time scale:
In simulation, the time scale used in data processing when the time scale factor is not constant during a run.

variable trace:
A record of the names and values of variables accessed or changed during the execution of a program. Synonymous with data-flow trace, data trace.

variant part:
A part of a record, composed of data objects, whose corresponding data structures or declared data types may vary. Both the number of data objects and their composition may vary.

variant record:
A record that contains a variant part. The record may contain discriminants to indicate the data types in the variant part.

variant record type:
A record type that has a variant part specifying alternative lists of components.

variation name:
(1) In an information resource dictionary, a character string used to identify each of several logically related entities with the same assigned access name or descriptive name. (2) A component of the version identifier of an entity in an information resource dictionary.

video display terminal.

video display unit.

(1) A quantity usually characterized by an ordered set of scalars. (2) A directed line segment. Contrast with scalar.

vector display device:
A display device that generates a display image as a series of vectors drawn from point to point in a systematic sequence. The display image is regenerated or refreshed to avoid fading. Synonymous with vector-refresh display.

vector generator:
A functional unit that generates directed line segments.

Translation of a bit-mapped image into an image defined by vectors.

vector processor:
Synonym for array processor.

vector-refresh display:
Synonym for vector display device.

Veitch diagram:
With respect to a specific logic expression containing n variables, an n-dimensional matrix with individual cells marked to indicate whether or not the logic expression is satisfied for various combinations of values for the n variables. Contrast with Karnaugh map. (Figure 61 - Veitch diagram).

Venn diagram:
A diagram in which sets are represented by regions and relationships between sets are represented by region overlaps. (Figure 62 - Venn diagram).

Comparing an activity, a process, or a product with the corresponding requirements or specifications; for example, comparing the performance of a module with its specifications.

verification test:
A test of a system to prove that it meets all its specified requirements at a particular stage of its development.

To determine whether a transcription of data or other operation has been accomplished accurately.

A service that provides an index to Gopher sites to build a customized menu of items on the Internet.

version space:
The subset of the concept descriptions such that the descriptions are either consistent with the available data, knowledge, or assumptions, or that they satisfy some associated criteria such as closeness of match.

vertical format:
Synonym for portrait.

vertical formatting:
Synonym for vertical tabulation.

vertical resolution:
The reciprocal of the number of pixels per linear measure along the vertical direction of the image.

vertical scrolling:
Synonym for rolling.

vertical synch:
The portion of a composite video signal that controls the timing for vertical sweep.

vertical tabulation:
The capability of a text editor to position text vertically within limits defined by the user. Synonymous with vertical formatting.

vertical tabulation character (VT):
The format effector that causes the printing position or display position to move to the corresponding position on a line, a predetermined distance away.

very-long instruction word processor:
Synonym for VLIW processor.

vibrotactile actuator:
A set of tiny crystals that vibrate, embedded in a glove output device or a body suit.

Data in a format suitable for a display as one or more images; for example: the content of a video cassette of a movie; the signal from a weather radar. Video is usually presented as a series of images in a manner to give the impression of action or changing conditions.

video conferencing:
Teleconferencing that provides transmission of still or moving images of participants, in addition to sound, text, and graphics. (Figure 60 - Teleconferencing).

video display terminal (VDT):
A user terminal with a display screen, and usually equipped with an input unit such as a keyboard.

video display unit (VDU):
Synonym for video display terminal.

video RAM (VRAM):
(1) A type of RAM used for high speed image processing. (2) Synonym for frame buffer.

video server:
A server distributing video services on demand.

video signal:
A signal in a format for display as one or more images.

video signal frame:
All of the signal needed to produce a single image; for example, the 525 lines of standard NTSC Television.

A service that provides interactive exchange of alphanumeric and graphics information over a telecommunication network; this information is displayed on a screen.

video transmission:
Electronic transfer of images from one point to another over a network.

(1) In computer graphics, any one of the possible representations of a three-dimensional object. (2) Synonym for subschema.

Application software that enables a user to have read access to documents.

viewing transformation:
Synonym for window/viewport transformation.

A predetermined part of a display space.

voice interactive response system.

Pertaining to something that appears to have some characteristics of something else for which it serves as a surrogate.

virtual address:
In a virtual storage system, the address assigned to a storage location in external storage to allow that location to be accessed as though it were part of main storage.

virtual call facility:
A user facility in which a call set-up procedure and a call clearing procedure determine a period of communication between two data terminal equipment in which user data are transferred through the network in the packet transfer mode. Data are usually delivered from the network in the same order as they were received by the network.

virtual copresence:
Synonym for electronic copresence.

virtual disk:
A portion of a physical disk that certain virtual machine operating systems can access as if it were logically a seperate disk.

virtual environment:
Synonym for virtual world.

virtual exploration:
The cognitive exploration of data, represented in some form, by navigating through the virtualized data.

virtual file:
A selected set of data objects, such as in a database management system, that is accessed as if it were a separate file.

The creation of a virtual object from data representing visual, aural, or other kinds of perceptions.

virtual local area network (VLAN):
A computer network using internetworks as data links that are transparent to the users and which do not impose restrictions on protocols, such that this network behaves like a local area network. Data links over internetworks typically use tunneling.

virtual machine (VM):
A data processing system that appears to the user as having characteristics different from those of the underlying machine or its real-world operation.

virtual memory (VM):
A storage implementation that extends the apparent size of memory by using a large address space that is dynamically mapped into real memory addresses, and by swapping data from external storage into memory as required.

virtual model:
Synonym for virtual-reality model.

virtual navigation:
The virtual exploration of data represented in visual form.

virtual object:
A computer-generated object or other effect within a virtual world.

virtual office:
A working environment whose employees work together from different locations using a computer network. Synonymous with virtual workplace.

virtual page:
A fixed-length block that has a virtual address and that is transferred as a unit between real memory and external storage.

virtual private network (VPN):
A network that uses the Internet for securely interconnecting nodes to form a virtual network.

virtual pushbutton:
A pushbutton simulated on a screen, that can be activated by a pointing device. Synonymous with light button.

virtual reality (VR):
The perceptions by and experiences of a participant in a virtual world.

virtual-reality author:
A designer or programmer of virtual worlds. Synonymous with VR author.

virtual-reality model:
A graphics model that represents a virtual object. Synonymous with VR model, virtual model.

Virtual Reality Modeling Language:

virtual reality realization:
The process by which a person interprets a patterned sensory impression to be a three-dimensional object. Synonymous with VR realization, three-dimensional visualization, cyberspace representation.

virtual space:
In computer graphics, a space in which the coordinates of the display elements are expressed in a device-independent form. (Figure 63 - Window/viewport transformation).

virtual terminal (VT):
A generalized logical model of different terminals of a certain class, describing how terminals of that class will perform.

virtual universe:
Synonym for virtual world.

virtual workplace:
Synonym for virtual office.

virtual world:
An environment that appears to have some characteristics of something else, and in which the participants perceive themselves as interactive parts. Each participant must perceive at least a three-dimensional universe. In the case of a multi-participant virtual world, the participants must be able to perceive their respective symbols. In virtual worlds the participants can interact using specialized peripheral equipment such as data gloves and head-mounted displays. Synonymous with virtual universe, virtual environment.

virtual-world generator:
The part of an artificial-reality engine that receives and processes the data to maintain a virtual world and presents it to the participants.

virtual-world interior:
The part of a virtual world that resides in the brain and body of the participant rather than in physical equipment. Synonymous with cyberspace interior.

virtual-world room:
An infrastructure to create a virtual world. A virtual-world room may contain wall-sized screens, stand-alone color monitors, eye-tracking, voice-input, and gesture-recognition devices. Synonymous with cyberspace room.

A program that propagates itself by modifying other programs to include a possibly changed copy of itself and that is executed when the infected program is invoked. A virus often causes damage or annoyance and may be triggered by some event such as the occurrence of a predetermined date.

virus signature:
A unique bit string that is common to each copy of a particular virus and that may be used by a scanning program to detect the presence of the virus.

(1) The ability to make a reference to a particular language construct at a specific place in a module. (2) The portion of a program within which a reference can be made to a specific language construct.

visible layer:
In artificial neural networks, a layer whose nodes directly communicate with external systems.

visible neuron:
An artificial neuron that directly communicates with external systems. A visible neuron may be an input neuron, an output neuron, or both.

visible part:
That part of a package declaration that provides details required by users of objects or services of the package.

vision sensor:
A functional unit that receives light energy from an environment and produces an output for further processing.

vision system:
A system capable of acquiring one or more images using an optical non-contact sensing device capable of measuring, analyzing, and processing various characteristics so decisions can be made. Functions of vision systems may include location, inspection, identification, recognition, and motion tracking.

visual clue:
The visual information about objects sufficient to give orientation and position information.

Synonym for scientific visualization.

virtual local area network.

VLIW processor:
A processor whose architecture combines many simple instructions into a single long instruction word that uses different registers. Synonymous with very-long instruction word processor.

virtual machine, virtual memory.

vocabulary-dependent recognition system:
Synonym for vocabulary-dependent recognizer.

vocabulary-dependent recognizer:
A speech recognizer that can recognize only words and sentences that are included in a given list. Synonymous with vocabulary-dependent recognition system.

vocabulary-independent recognition system:
Synonym for vocabulary-independent recognizer.

vocabulary-independent recognizer:
A speech recognizer that is not limited to a list of words or sentences defined previously or given online. Synonymous with vocabulary-independent recognition system.

A speech coding device that extracts speech signal parameters that allow the intelligible reconstruction of the initial speech signal. Synonymous with voice coder.

A sound produced in the larynx and uttered in the mouth. The sound need not be speech. Synonymous with human voice. (Figure 60 - Teleconferencing).

voice coder:
Synonym for vocoder.

voice command:
Deprecated synonym for spoken command.

voice control:
Control of a machine by means of spoken commands; for example, controlling a text processor by the use of spoken commands. Synonymous with speech control.

voice controller:
Synonym for voice control system.

voice control system:
A system in which a speech recognizer issues commands to computer-controlled equipment in response to speech input; for example, a robot that responds to simple spoken commands for movement. Synonymous with voice controller.

A spoken message recorded and transmitted to one or more recipients.

voice input:
Voice signals received by a functional unit.

voice interactive response system (VIRS):
A functional unit for interactive voice response.

voice mail:
A digitized voice message that is stored and forwarded to one or more recipients.

voice menu:
Synonym for spoken menu.

voice modem:
A modem that can support voice applications and data-handling functions.

voice output:
Deprecated synonym for speech output.

Synonym for voice signature.

voice prompt:
A spoken message used to guide the user through a dialog with a voice response system.

voice recognition:
The identification of the acoustic features of a human voice through analysis of a representation of a voice signals. Voice recognition is used in speaker recognition.

voice-recognition unit:
A functional unit that recognizes a limited number of spoken words and converts them to equivalent digital signals which can serve as computer input or initiate other desired actions. Such primitive peripheral equipment may be used with or without a speech recognizer.

voice response (VR):
A synthesized speech signal provided in reply to a user request.

voice-response prompt:
Synonym for voice prompt.

voice server:
A server that provides voice response.

voice signal:
An acoustic signal consisting of voice. Voice signals are all humanly produced; speech may be simulated.

voice signature:
A voice sample of a particular speaker used for identification purposes. Synonymous with voiceprint.

voice transmission:
Electronic transfer of voice from one point to another over a network.

In character recognition, the inadvertent absence of ink within a character outline.

volatile storage:
A storage device whose contents are lost when power is cut off.

A data medium, in a container that can be handled conveniently as a unit, and any data it may hold; for example, a reel of magnetic tape, a disk pack.

volume element:
Synonym for voxel.

volume modeling:
Synonym for solid modeling.

In computer graphics, the smallest three-dimensional element in solid modeling that can be independently assigned attributes such as color and intensity. The voxel has no internal structure and is typically derived by equidistantly dividing the three-dimensional space. Synonymous with 3-D pixel, volume element.

voxel value:
A discrete value that represents color, intensity, and other attributes of a voxel.

virtual private network.

Synonym for voice response, virtual reality.

video RAM.

VR author:
Synonym for virtual-reality author.

A standardized modeling language for describing a three-dimensional virtual world that can be viewed and manipulated interactively. VRML is the abbreviation for Virtual Reality Modeling Language.

VR model:
Synonym for virtual-reality model.

VR realization:
Synonym for virtual reality realization.

The vertical tabulation character, virtual terminal.

A weakness or flaw in a data processing system. If there is a threat that corresponds to such a vulnerability, then a risk exists. (Figure 57 - Levels of security risks).

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