D, E & F

DASD : Direct Access Storage Device. IBM nomenclature for a storage peripheral that can respond directly to random requests for information; usually denotes a disk drive.

Data Base (Base de Donn‰es) : Refer to DBMS.

Data Dictionary : A repository of information about data, such as its meaning, relationships to other data, origin, usage and format. The dictionary assists company management, database administrators, systems analysts and lication programmers in effectively planning, controlling and evaluating the collections, storage and use of data. A data dictionary manages data categories such as alias, data elements, data records, data structure, data store, data models, data flows, data relationships, processes, functions, dynamics, size, frequency, resource consumption and other user-defined attributes.

Data Model : The logical data structure developed during the logical database design process is a data model or entity model . It is also a description of the structural properties that define all entities represented in a database and all the relationships that exist among them.

Data Set Ready (DSR) : Signal emitted by a modem indicating that it is ready to exchange signals with the computer.

Data Terminal Ready (DTR) : Signal emitted by a computer indicating that it is ready to exchange signals with the modem.

DBA : Database Administrator. The person responsible for managing data at a logical level, namely data definitions, data policies and data security.

DB/DC : Database/Data Communication.This acronym refers to IBM's collection of transaction managers and database managers, e.g., Customer Information Control System, Information Management System, Database-2 and SQL/DS.

DBMS : Database Management System. A complete software facility for building, maintaining and generating reports from a database. It has evolved along three generic forms :

hierarchical DBMS (1960s) - records were organised in a pyramid-like structure, with each record linked to a parent
network DBMS(1970s) - records could have many parents, with embedded pointers indicating the physical location of all related records in a file
relational DBMS (1980s) - records were conceptually held in tables, similar in concept to a spreadsheet. Relationships between the data entities were kept separate from itself. Data manipulation created new tables, called views.

DCE : Distributed Computing Environment. DCE is the Open Software Foundation's solution to the problems of interconnectivity in a heterogeneous computing environment, standards and security. The DCE is composed of two sets of services : fundamental services from Digital Equipment Corp., Hewlett-Packard, the Massachusetts Institute of Technology, and Siemens, and data-sharing services from Microsoft, Sun Microsystems and Transarc. DCE integrates remote procedure calls, presentation services, a naming directory, security, threads (sequential flow of control similar to task) , time services (to synchronise clocks in a DCE) and a distributed file system.

Default value (Valeur par Defaut) : Implicitly used value, when no explicit value has been used by the user.

Dell Computer : US PC manufacturer, among the 5 largest in this businessDensityMeasure of the quantity of data that can be registered by longitudinal inch on a mass storage unit such as a disk drive.

Dial UP : The process of, or the equipment or facilities involved in, establishing a temporary connection via the switched network.

Dialog box (Boite de dialogue) : Rectangle displayed on the screen after selecting certain menu options. Dialog boxes propose complementary options in relation with the requested operation.

Digital (DEC) : Digital Equipment Corporation, Maynard, California. Third worldwide computer manufacturer, recentered on processors business, and more especially the 64-bit Alpha chip

Digitizers : A purely graphical input device - i.e., a computer-aided design/computer-aided manufacturing system device used in computer-aided engineering for converting locations into storable electronic impulses - with a surface on which a location or point is selected and then automatically converted into a digital X-Y co-ordinate suitable for transmission to a computer.

DIP : Dual In-Line Package. Standard format for integrated circuits manufacturing, in which silicon-engraved microcircuits are embedded in a rectangular plastic or ceramic container, and connected on each long side of the circuit through pins directed towards the bottom.

Disk Mirroring : The duplication of disks and controllers so that two access paths exist in case a failure occurs on one of them.

Diskette Medium used to store data. The magnetic support is protected by a plastic cartridge. The capacity of 3.5 inch diskettes is 1.4 MB (in High Density mode).

Display : Unit such as CRT or LCD allowing the user to read information produced by the computer.

Distributed Database : A database whose objects (tables, views, columns and files) reside on more than one system in a network, and can be accessed or updated from any system in the network.

DMA : Direct Memory Access. Process allowing to exchange data between the central storage and an I/O device without passing through the CPU.

DME : Distributed Management Environment. From the Open Software Foundation, DME will result in architectures and services that will simplify systems management applications across multiple platforms. DME includes such tasks as backup/restore, printing services, software installations, software distribution and user management. A more global initiative allows organisations to have a consistent approach to managing their systems.

DOS : Disk Operating System (or Dirty Operating System ?). Developed by Microsoft, it became a standard when bought by IBM, in 1981.

Double click : Operation consisting in pressing quickly twice the mouse button without moving the mouse

Downsizing : The process of moving computing work to a smaller computer. More generally, it is often applied to applications that might otherwise have been implemented on a big computer, being brought up on a small computer.

DPI : Dots Per Inch. A measurement of resolution ; e.g., the number of pixels per inch on a cathode-ray tube display.

DRAM : Dynamic Random Access Memory. Type of main storage that require a permanent rewrite (each some milli-seconds), as opposed to Static RAM. In 1995, access time is in the range 50-80 nano-seconds.

E

EBCDIC : Extended Binary Coded Decimal Interchange Code. IBM specific code mapping characters on an 8 bit format.

ECC : Error Correcting Code. The diagnostic code used to correct data storage errors and to isolate hardware failures. Based on a concept of simultaneous polynomial equations, the read-back process generates a "correction" profile that is exclusive-OR'ed over the incorrect data. All ECCs have a very small, but finite failure rate; that is, some uncorrectable errors will either appear as correctable or appear as having no error at all. In either situation, bad data is passed as verified and valid.

ECMA : European Computer Manufacturers Association. Develops standards for submission to International Standards Organisation and the Comit‰ Europ‰en de Normalisation.

EDI : Electronic Data Interchange. The electronic transfer of preformatted business documents, such as purchase orders and bills of lading, between trading partners.

EDIFACT : Electronic Data Interchange for Administration, Commerce and Transportation. An EDI standards development group.

EGA : Enhanced Graphic Adapter. Ancient video standard allowing graphical color display ( resolution 640x340 in monochrome).

EIA : Electronic Industries Association, in charge of defining norms in the USA.

EISA : Extended Industry Standard Architecture. This is an extension of the standard ISA bus interface, which specifies on personal computers (PC compatible) the physical and logical characteristics of the interface. EISA has a 32 bit-wide interface. An EISA slot can also be used for an 8 or 16 bit ISA PCB.

E-Mail (Electronic Mail) : Software allowing to compose, transmit and receive messages and attached/enclosed files.

Emulation : Mode in which a system imitates another one in order to exploit the same programs or to provide the same results. Emulation facilitates conversion.

Energy Star : Norm defined by the EPA (US Environment Protection Agency) for computer manufacturers aiming at reducing electrical consumption.

Error control : Strategy implemented in software, hardware or procedures for detecting and possibly correcting the errors happening in a communication system.

ESDI : Enhanced Small Device Interface. Disk connection interface. The SDSI standard is replacing ESDI.

Ethernet : A baseband local-area network developed by Xerox Corp. It has a bus topology with Carrier Sense Multiple Access/Collision Detection access control. An Ethernet network provides a raw 10 Mbps, with an effective throughput around 2-3 Mbps. Ethernet networks characteristics are defined in norm IEEE 802.3.

Excel : Microsoft spreadsheet.

Expert System (Systˆme expert) : A software system with two basic components: a knowledge base and an inference engine. The system mimics an expert's reasoning process.

F

Facsimile : A system for the transmission (usually over a voice-grade channel) of a picture, drawing or document, with reproduction at the receiving end.

FAT : Slim-Fast is useless to eliminate it ! File Allocation Table. In a DOS system, this table contains for each file its address on the disk.

Fault Tolerance : The ability to produce correct results, even in the presence of faults or errors, by the use of redundancying hardware or checking techniques.

Fax : Abbreviation for facsimile.

FCC : Federal Communications Commission. The U.S. federal agency responsible for regulating interstate telecommunications, as well as international telecommunications aspects of cellular communications and broadcasting. The FCC was established by the Communications Act of 1934.

FDDI : Fiber Distributed Data Interface. An American National Standards Institute standard for 100 Mbps fiber-optic local area networks. Incorporates token processing and supports circuit-switched voice and packetized data. Components include: PMD (Physical Layer Medium Dependent), which deals with physical connections including fiber links, cables and connectors.; PHY (Physical Layer Protocol) which includes the encoding/decoding of packets and data clocking; MAC (Media Access Control) which includes parameters for token passing, addressing, packed sizes and framing; and SMT (Station Management) which governs management of the physical network.

Fiber Optics (Fibres optiques) : A high-bandwidth transmission technology that uses light to carry digital information. One fiber telephone cable carries hundreds of thousands of voice circuits. These cables, or light guides, replace conventional coaxial cables and wire pairs. Fiber transmission facilities occupy far less physical volume for an equivalent transmission capacity, which is a major advantage in crowded ducts. Optical fiber is also immune to electrical interference.

File (Fichier) : Set of apparented records considered as a unit for storage.

File Server (Serveur de fichiers) : A computer containing files available to all users connected to a local-area network (LAN). In some LANs, a microcomputer is designated as the file server, while in others it is a computer with a large disk drive and specialised software. Some file servers also offer other resources such as gateways and protocol conversion.

Filter (Filtre) : Process limiting the computation, display and printing to specified information.

Flash ROM : ROM storage able to be updated, deleted or reprogrammed.

Font : Character style used by a program in order to display or print a text.

Formal Standards : Specifications or styles that are approved by vendor-independent standards bodies, such as the American National Standards Institute, the International Standards Organisation, the Institute of Electrical and Electronics Engineers, and the National Institute for Standards and Technology.

Fragmentation : File division in physically separated segments in a disk. Fragmentation is due to file increase in a highly used disk, thus leading to a lack of sufficient contiguous free space.

Frame Relay : An International Telegraph and Telephone Consultative Committee (CCITT) recommendation (I.122) and American National Standards Institute standard (T1S1). Frame relay is an ISDN (Integrated Services Digital Network) packet-mode bearer service that defines a user-to-network interface. The two main benefits are bandwidth on demand and integrated access. The standard currently addresses data communications speeds up to 2 Mbps over permanent virtual circuits. By reducing the network functions performed, frame relay takes advantage of more robust physical facilities to improve throughput.

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