D

DAO

See also Data Access Objects (DAO).

Data Access Objects (DAO)

An older data access technology introduced by Microsoft that relies on the Microsoft Access JET engine for local data access. DAO does not provide remote access features; although, some programmers have been able to establish unreliable connections with it. ActiveX Data Objects (ADO) and Object Linking and Embedding - DataBase (OLE-DB) have largely replaced this technology.

Data Source Name (DSN)

A name assigned to an Open Database Connectivity (ODBC) connection. Applications use the DSN to make the connection to the database and gain access to specific database resources such as tables. The DSN always contains the name of the database server, the database, and ( optionally ) a resource like a query or table. Many database technologies such as Object Linking and Embedding-DataBase (OLE-DB) rely on the use of DSN connection information.

Database Management System (DBMS)

A method for storing and retrieving data based on tables, forms, queries, reports , fields, and other data elements. Each field represents a specific piece of data, such as an employee's last name. Records are made up of one or more fields. Each record is one complete entry in a table. A table contains one type of data, such as the names and addresses of all the employees in a company. It's composed of records (rows) and fields ( columns ), just like the tables you See in books. A database may contain one or more related tables. It may include a list of employees in one table, for example, and the pay records for each of those employees in a second table. Sometimes referred to as a Relational Database Management System (RDBMS) that includes products such as SQL Server and Oracle.

DBMS

See also Database Management System (DBMS).

DCOM

See also Distributed Component Object Model (DCOM).

DDE

See also Dynamic Data Exchange (DDE).

Delimiter

1. A special symbol or symbols used to separate text. For example, many programming languages use the single ( ˜) or double ( ) quote to separate text elements. 2. A boundary between two different objects. The boundary normally consists of a special symbol or group of symbols. A delimited file contains variable length records. Each field normally uses a comma as a delimiter. Each record normally uses a carriage return as a delimiter.

Developer License

A special identifier issued by an organization to allow access to a resource such as a Web service. For example, Google issues a developer license to Google Web Services developers. The developer supplies this license for identification purposes when creating a Google Web Services application.

Digital Subscriber Line (DSL)

A term used to refer to any of a number of technologies that allow higher communication rates over standard telephone lines than normally allowed using standard modems. DSL is normally used between a remote location such as a home or office and the switching station or ISP. It isn't used between switching stations . Types of DSL include asynchronous DSL (ADSL), symmetric DSL (SDSL), and high bit-rate DSL (HDSL). The technologies vary by their ability to pack data onto the copper line, distance from the switching station, and other characteristics. ADSL allows communication from 1.5 Mbps to 9 Mbps downstream (to the remote connection) and 16 Kbps to 640 Kbps upstream (from the remote connection). SDSL allows communication up to 3 Mbps in both directions. HDSL allows communication up to 1.544 Mbps in both directions.

Digital Video Disc (DVD)

A high capacity optical storage media with capacities of 4.7GB to 17GB and data transfer rates of 600KBps to 1.3GBps. A single DVD can hold the contents of an entire movie or approximately 7.4 CD-ROMs. DVDs come in several formats that allow read-only or read-write access. All DVD drives include a second laser assembly used to read existing CD-ROMs. Some magazines will also use the term digital versatile disc for this storage media.

Distributed Component Object Model (DCOM)

A transport protocol that works with the component object model (COM), and is used for distributed application development. This protocol enables data transfers across the Internet or other non-local sources, but is usually limited to a Local Area Network (LAN) or Wide Area Network (WAN) environment. DCOM adds the capability to perform asynchronous, as well as synchronous, data transfers between machines. The use of asynchronous transfers prevents the client application from becoming blocked as it waits for the server to respond.

DLL

See also Dynamic Link Library (DLL).

DSL

See also Digital Subscriber Line (DSL).

DSN

See also Data Source Name (DSN).

DVD

See also Digital Video Disc (DVD).

Dynamic Data

Information that changes regularly due to internal or external events, as a result of the nature of the data, or consistent with a systematic or mathematical progression. For example, an application can provide automatic updates as it detects changes in the underlying data used for presentation. Many research sources, such as the Internet, now rely on dynamic data to reduce the effects of data aging.

Dynamic Data Exchange (DDE)

1. The capability to place data from one application on the Windows clipboard and paste it from the clipboard into another application. A user can cut a graphics image created with a paint program, for example, and paste it into a word processing document. After it's pasted, the data doesn't reflect the changes made to it by the originating application. The source and target applications must provide DDE functionality for this technology to work. They must also support the data formats required for the information exchange. 2. A method of communicating with an application that supports DDE when the application allows requests for data or services. The communication parameters include the application, the topic of the conversation, and a DDE message. In most cases, the DDE message consists of a series of menu or macro sequences that perform the desired task.

Dynamic Link Library (DLL)

A specific form of application code loaded into memory by request. It's not executable by itself like an EXE is. A DLL does contain one or more discrete routines that an application may use to provide specific features. For example, a DLL could provide a common set of file dialogs used to access information on the hard drive. More than one application can use the functions provided by a DLL, reducing overall memory requirements when more than one application is running. DLLs have a number of purposes. For example, they can contain device-specific code in the form of a device driver. Some types of COM objects also rely on DLLs.