Metadata (meta data, or sometimes metainformation) is "data about data", of any sort in any media. An item of metadata may describe an individual datum, or content item, or a collection of data including multiple content items and hierarchical levels, for example a database schema.

Purpose

Metadata provides context for data.

Metadata is used to facilitate the understanding, characteristics, and management usage of data. The metadata required for effective data management varies with the type of data and context of use. In a library, where the data is the content of the titles stocked, metadata about a title would typically include a description of the content, the author, the publication date and the physical location.

Camera

In the context of a camera, where the data is the photographic image, metadata would typically include the date the photograph was taken and details of the camera settings (lens, focal length, aperture, shutter timing, white balance, etc.).

Digital Music Player

On a digital portable music player, the album names, song titles and album art embedded in the music files are used to generate the artist and song listings, and are considered the metadata.

Information system

In the context of an information system, where the data is the content of the computer files, metadata about an individual data item would typically include the name of the field and its length. Metadata about a collection of data items, a computer file, might typically include the name of the file, the type of file and the name of the data administrator.

Real world location

If we consider a particular place in the real world, this may be described by data, for example:

• 1 "E83BJ" .
• 2 "17"
• 3 "Sunny"
• 4 "27 June 2006, 10:00"

To make sense of and use this data, context is important, and can be provided by metadata. The metadata for the above four items of data might include:

• 1 "Post Code" – This is a brief description (or name) of the data item "E83BJ." In this example, the physical place wherer the other data were observed.
• 2 "Average temperature in degrees Celsius" – This is a possible description of "17" at the identified place at the specified date and time.
• 3 "Yesterday's weather" – This is a description of "Sunny" at the identified place at the specified date and time.
• 4 "Date and time of observation: - This a description of "27 June 2006, 10:00" specifying when data points 2 and 3 were collected at the specified location.

An item of metadata is itself data and therefore may have its own metadata. For example, "Post Code" might have the following metadata:

• 1.1.1 "postal code data"
• 1.1.2 "5 alpha-numeric characters"
• 1.1.3 "AnnAA, where A = alphabetical and n = numerical"