Generally, a directory, as used in computing

Computing

Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...

 and telephony

Telephony

In telecommunications, telephony encompasses the general use of equipment to provide communication over distances, specifically by connecting telephones to each other....

, refers to a repository

Digital library

A digital library is a library in which collections are stored in digital formats and accessible by computers. The digital content may be stored locally, or accessed remotely via computer networks...

 or database

Database

A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...

 of information which is heavily optimized for reading, under the assumption that data updates are very rare compared to data reads. Commonly, a directory supports search and browsing in addition to simple lookups.

A website which offer access to a categorized listing of other websites optimized for lookup, search, or browsing is a directory, a web directory

Web directory

A web directory or link directory is a directory on the World Wide Web. It specializes in linking to other web sites and categorizing those links....

. The Open Directory Project

Open Directory Project

The Open Directory Project , also known as Dmoz , is a multilingual open content directory of World Wide Web links. It is owned by Netscape but it is constructed and maintained by a community of volunteer editors.ODP uses a hierarchical ontology scheme for organizing site listings...

 is an example of a web directory.

Directory technology is often used in white page applications and network information services.

WHOIS

WHOIS

WHOIS is a query and response protocol that is widely used for querying databases that store the registered users or assignees of an Internet resource, such as a domain name, an IP address block, or an autonomous system, but is also used for a wider range of other information. The protocol stores...

 is a prominent example of directory service providing white pages.

The Domain Name System

Domain name system

The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...

 (DNS) is a prominent example of directory service providing a network information service. DNS is also an example of a distributed

Distributed computing

Distributed computing is a field of computer science that studies distributed systems. A distributed system consists of multiple autonomous computers that communicate through a computer network. The computers interact with each other in order to achieve a common goal...

 hierarchical directory service

Directory service

A directory service is the software system that stores, organizes and provides access to information in a directory. In software engineering, a directory is a map between names and values. It allows the lookup of values given a name, similar to a dictionary...

 that only has simple lookup capabilities.

The X.500

X.500

X.500 is a series of computer networking standards covering electronic directory services. The X.500 series was developed by ITU-T, formerly known as CCITT, and first approved in 1988. The directory services were developed in order to support the requirements of X.400 electronic mail exchange and...

 and LDAP

Lightweight Directory Access Protocol

The Lightweight Directory Access Protocol is an application protocol for accessing and maintaining distributed directory information services over an Internet Protocol network...

 directory services are examples of general-purpose distributed hierarchical object-oriented directory technologies. Both offer complex searching and browsing capabilities and are used for white pages, network information services, public key infrastructure

Public key infrastructure

Public Key Infrastructure is a set of hardware, software, people, policies, and procedures needed to create, manage, distribute, use, store, and revoke digital certificates. In cryptography, a PKI is an arrangement that binds public keys with respective user identities by means of a certificate...

, and a wide range of other applications.

See also

• Database
  Database
  A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
  
  
• Directory service
  Directory service
  A directory service is the software system that stores, organizes and provides access to information in a directory. In software engineering, a directory is a map between names and values. It allows the lookup of values given a name, similar to a dictionary...
  
  
• Reference works
• Web directory
  Web directory
  A web directory or link directory is a directory on the World Wide Web. It specializes in linking to other web sites and categorizing those links....
  
  
• RSS directory