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developmental baseline:
The specifications that are in effect at a given time for a system under development.

device control character:
A control character used to specify a control function for peripheral devices associated with a computer system. (Figure 12 - Character taxonomy).

device coordinate:
A coordinate specified by a device-dependent coordinate system.

device space:
The space defined by the complete set of addressable points of a display device.

device transformation:
A coordinate transformation from normalized device coordinate to device coordinate.

Pertaining to the detection, analysis, or description of faults, failures, or mistakes.

diagnostic function:
The capability of a functional unit to detect problems and to identify the type of error.

diagnostic program:
A program that is designed to detect, locate, and describe faults in equipment or errors in programs.

dial back:
Synonym for callback.

dialog box:
A pop-up window into which data may be entered.

dialog component:
In artificial intelligence, the component of an expert system or knowledge-based system that interfaces with the user in a conversational manner.

The service whereby a functional unit can use the telephone to initiate and effect communication with another functional unit.

A group of sounds usually recognized as being the same although pronounced with slight differences by various speakers.

A problem-oriented language used for developing business applications. The name is derived from Digital Business-Oriented Language.

dichotomizing search:
A search in which an ordered set of data elements is partitioned into two mutually exclusive parts, one of which is rejected; the process is repeated on the accepted part until the search is completed.

difference detection:
A process by which two images may be compared, pixel by pixel, in order to determine whether corresponding resolution cells have significantly different attribute values.

differential amplifier:
An amplifier that has two input circuits and that amplifies the difference between the two input signals.

differential encoding:
Encoding of a digital data stream in which each element except the first is represented as the difference in value between that element and the previous element.

differential Manchester encoding:
A binary phase encoding in which the time interval assigned to each bit is divided in half by a transition and the presence or absence of another transition at the beginning of this time imterval determines the value of the bit, i.e., a "0" or a "1", respectively. The transition may occur between two states of a physical variable such as voltage, magnetic polarity, or light intensity. If the physical variable is electrical, this type of encoding is polarity-independent and is free of a DC component. (Figure 20 - Manchester and differential Manchester encoding).

Diffie-Hellman cryptosystem:
One of several systems for public-key cryptography.

A character that represents a natural number. For example, one of the characters 0 through 9 in the decimal system; these digits plus the characters A through F used in the hexadecimal system. The mathematical term "natural number" denotes all nonnegative integers. Synonymous with numeric character. (Figure 12 - Character taxonomy).

Pertaining to the representation of data by distinct states or discrete values, and more specifically to data that consist of digits, to processes, or to functional units that use such data.

digital cash:
Synonym for electronic cash.

digital computer:
(1) A computer that operates on discrete data. (2) A computer that accepts, processes, or produces digital data. The term computer is often used to refer to a digital computer.

digital data:
Data represented by digits, possibly together with special characters and the space character.

digital image:
An image consisting of pixels using ranges of discrete values. Example: An image sampled and encoded using discrete values for brightness and hue. Contrast with analog image.

digital optical disk:
Synonym for optical disk.

digital representation:
A discrete representation of a quantized value of a variable, i.e., the representation of a number by digits, perhaps with special characters and the space character.

digital signal:
A signal that can be used to represent data in a form that is encoded as digits. One form of such a signal is one that may be characterized as consisting of a finite number of relatively stable states that occur for a significant duration and with relatively short transition times between these values. Another form, is through the generation of waveforms such that each may be easily characterized as belonging to one and only one of a limited class of waveforms. (Figure 21 - Components of an idealized discrete signal)

digital signal processor (DSP):

digital signature:
Data appended to a message, that allow the recipient of the message to verify the source of the message.

digital-to-analog converter (DAC):
A functional unit that converts data from a digital representation to an analog representation. Synonymous with D/A converter.

digital versatile disk:

digital video disk:

To express or represent data that are not discrete data in a digital form; for example, to obtain a digital representation of the magnitude of a physical quantity from an analog representation of that magnitude.

digitized data:
Values that have been quantized and represented in digital form.

digitized image:
A digital representation from which a display image can be generated.

An input unit for converting analog data into digital form.

digit place:
In positional notation, each position that may be occupied by a digit and that is identified by an ordinal number or by an equivalent. Synonymous with digit position.

digit position:
Synonym for digit place.

A geometrical operation that increases the size of a object. Synonymous with expansion.

diluted network:
Synonym for partially connected network.

diminished radix complement:
In fixed-radix notation, a complement that can be derived from a given number by subtracting it from one less than a specified power of the radix. For example: in the decimal system using three digits, 829 is the diminished radix complement of 170, one less than the power of the radix being 999 (=103-1). A diminished radix complement may be obtained by subtracting each digit of the given number from a digit that is one less than the radix. Synonymous with radix-minus-one complement.

A speech segment extending from the stable part of one phoneme to the stable part of the following phoneme and containing the transitional part.

direct access:
The capability to obtain data from a storage device, or to enter data into a storage device, in a sequence independent of their relative position, by means of addresses that indicate the physical location of the data.

direct access storage:
A storage device that provides direct access to data.

direct access storage device (DASD):
Peripheral equipment in which access is achieved without the necessity of sequencing through the data.

direct address:
An address that identifies a location without reference to a storage location containing another address. The location may be a storage location or a device.

direct call facility:
A facility through which the data network interprets the call request signal as an instruction to establish a connection to one or more data stations previously designated by the user, thereby relieving the user of the need to provide address selection signals during call set-up. This facility may permit a faster call set-up than usual. No special priority is implied over other users of the data station establishing a connection. The designated addresses are assigned for an agreed period of time.

directed-beam display device:
Synonym for calligraphic display device.

direct instruction:
An instruction that contains the value of an operand rather than its address. Synonymous with immediate instruction.

In Pascal, the term for compiler directive.

directly recursive:
Pertaining to a subprogram that contains a call on itself.

direct memory access (DMA):
A technique for moving data directly between main storage and peripheral equipment without requiring processing of the data by the processing unit.

direct numerical control (DNC):
Numerical control in which one or more machine tools are connected directly or via a data line to a source of numerically coded commands.

(1) In electronic mail, an organized list of the users or services that can be addressed on a network. (2) An organized list of file names and associated data such as location on a data medium. (3) In OSI, a logical database about objects in the real world as maintained by cooperating open systems.

directory facility:
In OSI, an application service that translates the symbolic names used by application processes into the complete network addresses.

directory information base:
The set of information managed by the directory system.

directory information tree:
The tree structure used in the directory system to identify objects unambiguously by means of directory names. This tree structure is mapped onto the directory names by composing a name from the nodes leading to the specific entry.

directory management domain (DMD):
A collection of one or more directory system agents, and possibly several directory user agents, that is managed by a single authority.

directory name:
An identifier of a particular object, organized according to the rules in the directory system. A directory name must be unambiguous (that is, denote just one object), however it need not be unique (that is, be the only name which unambiguously denotes the object).

directory system:
A collection of open systems cooperating to provide directory services.

directory system agent (DSA):
A functional unit of the directory system that provides access to the information contained in the directory information base.

directory user:
A person or a functional unit that accesses the directory system.

directory user agent (DUA):
A functional unit by means of which a directory user interacts with a directory system.

direct overwrite:
A thermo-magnetic recording method using a specially designed medium that does not require a separate erase pass.

direct overwrite disk:
A disk in which the new data can be written directly over old data by modulating the laser intensity without reversing the magnetic field direction. Synonymous with DOW disk.

direct overwrite magneto-optical disk:
A magneto-optical disk that requires no separate erase procedure of previously written data prior to writing new data. Synonymous with DOW MO disk.

direct percentage function:
The function that directly calculates a percentage markup or discount value.

direct submission:
A submission in which a user agent or a message store conveys a message or probe directly to a message transfer agent without going through any intermediate functional units.

direct user:
A user that engages in message handling by direct use of the message handling system.

direct waveform synthesis:
A simple method for speech synthesis that consists in recording speech signals (either in digital or analog form) and then playing them back on demand according to the needs of the application. Direct waveform synthesis method may introduce access time delays and will be limited in capacity by the recording medium available, but the artificial speech will generally be of high quality.

The action of determining which language construct, of several with the same sequence of lexical tokens, is referred to by a particular occurrence within a program.

To translate object code to an assembly language representation.

disaster dump:
A dump made when a nonrecoverable error occurs in a program.

disaster plan:
Synonym for contingency plan.

disaster recovery plan:
Synonym for contingency plan.

Alternate spelling for disk, especially as in compact disc.

In computer security, a violation whereby data have been made available to unauthorized entities.

disclosure of other recipients service:
A service that enables the originator's user agent to instruct the message transfer system when submitting a multirecipient message, to disclose the O/R names of all other recipients to each recipient's user agent, upon delivery of the message.

Pertaining to data that consist of distinct elements, such as characters, or to physical quantities having a finite number of distinctly recognizable values, as well as to processes and functional units that use those data.

discrete data:
Data that consist of distinct elements, such as characters, or that can be represented by one or more distinctly recognizable values, such as integers. Discrete data may be characterized by their ability to be mapped to the set of integers. Contrast with analog data.

discrete representation:
A representation of data by characters, where each possible value is expressed by a distinct character or group of characters. Contrast with analog representation.

discrete-speech recognition:
Synonym for isolated-words recognition.

discretionary access control:
A means of optionally restricting access to objects, based on the identity of subjects, the groups to which they belong, or both of these criteria. Access controls are discretionary in the sense that a subject with a particular access right can pass that access to any other subject. Contrast with mandatory access control, need-to-know.

discretionary hyphen:
Synonym for soft hyphen.

A parameter-like language construct that indicates the data structure to be used within a given variant record.

discriminant description:
A concept description that states properties distinguishing a given concept from other concepts under consideration.

discrimination network:
An artificial neural network in which the set of tests used to classify a collection of objects, situations, or events is implemented according to predetermined features.

discussion group:
Synonym for forum.

discussion thread:
On a bulletin board or in a forum, a sequence of postings in response to a single posting.

The logic operation whose result is True if any of its operands are True. Truth values are frequently represented by 1 and 0 as in Boolean operations. Synonymous with INCLUSIVE-OR, logical add, OR. (Figure 4 - Table of Boolean operations).

A data medium consisting of a flat, circular plate that is rotated in order to read or write data on one or both sides. Also spelled disc, especially as in compact disc.

disk buffer:
A buffer in which data are held before being written to or after being read from a disk.

disk cache:
A area of the main storage holding data that has recently been requested from disk or written to disk, and that are likely to be needed again.

disk cartridge:
An assembly of one or more disks that can be removed as a whole from a disk drive, together with the associated rigid container from which it cannot be separated.

disk drive:
A functional unit that can store on and retrieve data from rotating disks; for example, a floppy disk drive, a fixed disk drive, a CD-ROM drive. Techniques employed include magnetic storage and optical storage. It may be removable or fixed permanently attached within the device. Synonymous with disk unit.

Synonym for floppy disk.

disk pack:
An assembly of magnetic disks that can be removed as a whole from a disk drive, together with a container from which it must be separated when operating.

disk unit:
Synonym for disk drive.

To allocate time on a processor to jobs or tasks that are ready for execution.

That program in an operating system or another functional unit, the purpose of which is to dispatch.

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