Collections and Directories

Look up Collection in Wiktionary, the free dictionary

In common usage, a collection is any group of items that has one or more properties in common, usually brought together for some specific purpose. See Collecting and Collectibles.

The term can also be used more specifically:

• In mathematics, collection is not precisely defined, but can refer to various objects. Most often it refers to a set, class, family, or multiset.
• In museums and art galleries, the collection of objects in a particular field forms the core basis for the museum.
• In music, specifically diatonic set theory, a collection is similar to a tone row; see generated collection.
• In a church the collection is the money collected from the congregation during a service. The congregation normally place their donation into a collection plate or bag which is passed around and returned to the priest.
• Collection (Oxford Colleges) – college examinations in the University of Oxford.

This article is about the computing term. The Directory was also a government in revolutionary France from 1795 to 1799.

In computing, a directory, catalog, or folder, is an entity in a file system which contains a group of files and other directories. A typical file system contains thousands of files, and directories help organize them by keeping related files together. A directory contained inside another directory is called a subdirectory of that directory. Together, the directories form a hierarchy, or tree structure.

If you imagine the computer's file system as a file cabinet, high–level directories may be represented by the drawers, while lower–level subdirectories may be represented as file folders within the drawers.

Historically, and even on some modern embedded devices, the filesystems either have no support for directories at all or only have a flat directory structure, meaning subdirectories are not allowed; there is only a group of top–level directories each containing files. The first popular fully general hierarchical filesystem was that of UNIX. This type of filesystem was an early research interest of Dennis Ritchie.

In modern times in Linux and other Unix-like systems, directory structure is defined by either the Filesystem Hierarchy Standard or by [Modified Directory Structure].

The folder metaphor

The name folder, presenting an analogy to the file folder used in offices, is common on some operating systems such as Mac OS and, increasingly, Microsoft Windows.

Strictly speaking, there is a difference between a directory which is a filing system concept, and the WIMP metaphor that is used to represent it (a folder).

Note that the folder metaphor may be misleading with regard to things like file permissions on UNIX: To rename or delete a file you need write permission to the directory that contains the file. This is perfectly understandable if the directory is seen as a list of filenames but not if it is seen as a container (as folder implies).

In graphical user interface (GUI) or WIMP environments, folders are often depicted with icons which resemble physical file folders such as those of a file cabinet in an office.

See also

• Folder
• cd command
• Working directory
• Web directory

The word directory is also used in computing and telephony with a different meaning: a central repository of information related to management of a computer or a network of computers. This includes data on users, applications, hosts, network devices, security credentials and more. The directory, as opposed to a conventional database, is heavily optimized for reading, with the assumption that data updates are very rare compared to data reads.

As of 2003, the prominent directory technology is the Internet standards-track protocol LDAP, which is descended from the X.500 standard. Microsoft's implementation of LDAP is Active Directory. Most LDAP directories maintain information in a white pages schema which represents attributes of individual persons, groups and organizations.

The Distributed Management Task Force (DMTF) is also creating standards related to the representation of information stored in directories for system and network management, and the protocols and APIs used to access it. The main product of these efforts is a Common Information Model (or CIM) for management.

See also: directory service, web directory.