gloss_D

D

Data Access Language (DAL).

DAL is Apple's database query language that is based upon SQL, but it provides far greater functionality.

data dictionary.

In a distributed database, a data dictionary keeps track of where the data is located and stores the necessary information for determining the best way to retrieve the data.

Data Encryption Standard (DES).

DES is the United States government's standard for encryption, in which data is scrambled using security codes called keys, so data cannot be deciphered by unauthorized users.

database server.

A database server is a database application that follows the client-server model, dividing an application into a front end and a back end. The front end, running on the user 's computer, displays the data and interacts with the user. The back end, running on a server, preserves data integrity and handles most of the processor- intensive work, such as data storage and manipulation.

Data-link layer.

The Data-link layer is the second layer of the OSI model. It defines how data is framed and transmitted to and from each network device. It is divided into two sublayers : medium access control and logical link control.

DECnet.

Digital Equipment Corporation's network system for networking personal computers and host computers. DECnet can use TCP/IP and OSI, as well as its proprietary protocols.

departmental LAN.

A departmental LAN is a network that's used by a small group of people laboring toward a similar goal. Its primary goal is to share local resources, such as applications, data, and printers.

directory services.

Directory services provide a white pages-like directory of the users and resources that are located on an enterprise network. Instead of having to know a device or user's specific network address, a directory service provides an English-like listing for a user. The OSI's X.500, Novell's NetWare Directory Services (NDS), Microsoft's Active Directory, and Banyan's StreetTalk are examples of directory services.

distributed computing.

In a distributed computing architecture, portions of the applications and the data are broken up and distributed among server and client computers. In the older model, all applications and data resided on the same computer.

distributed database.

A database application where there are multiple clients as well as multiple servers. All databases at remote and local sites are treated as if they were one database. The data dictionary is crucial in mapping where the data resides.

Distributed Queue Dual Bus (DQDB).

The medium access method of the IEEE 802.6 standard for metropolitan area networks.

downsizing.

Downsizing or rightsizing is the process of porting mission-critical applications from a mainframe to a minicomputer or PC LAN or from a minicomputer to a PC LAN.

dual homing.

In FDDI, dual homing is a method of cabling concentrators and stations in a tree configuration that permits an alternate path to the FDDI network in case the primary connection fails.

Dual-Attached Station (DAS).

In FDDI, a DAS connects to both of the dual, counter-rotating rings. Concentrators, bridges, and routers often use DAS connections for fault tolerance. In contrast, a single-attached station is connected to only one ring.

Dynamic Data Exchange (DDE).

DDE is Microsoft's specification for Windows 3.1 and earlier versions that enables applications to communicate without human intervention.