Metadata

(meta data, or sometimes metainformation) is "data about data", of any sort in any media. Metadata is text, voice, or image that describes what the audience wants or needs to see or experience. The audience could be a person, group, or software program. Metadata is important because it aids in clarifying and finding the actual data.An item of metadata may describe an individual datum, or content item, or a collection of data including multiple content items and hierarchical levels, such as a database schema. In data processing, metadata provides information about, or documentation of, other data managed within an application or environment. This commonly defines the structure or schema of the primary data.

For example, metadata would document data about data elements or attributes, (name, size, data type, etc) and data about records or data structures (length, fields, columns, etc) and data about data (where it is located, how it is associated, ownership, etc.). Metadata may include descriptive information about the context, quality and condition, or characteristics of the data. It may be recorded with high or low granularity.

An example of metadata occurs within file systems. Associated with every file on the storage medium is metadata that records the date the file was created, the date it was last modified and the date the file (or indeed the metadata itself) was last accessed.

Purpose

Metadata provides context for data.

Metadata is used to facilitate the understanding, usage, and management of data, both by human and computers. Thus metadata can describe the data conceptually so that others can understand them; it can describe the data syntactically so others can use them; and the two types of descriptions together can facilitate decisions about how to manage the data.

The metadata required to effectively work with data varies with the type of data, their context of use, and their purpose. Often data providers will provide users access to a variety of metadata fields, which can be used individually or in combinations, and applied by different users to achieve different goals. These users can be human 'end users', or other computing systems. See also the Use section below for more details about the use of metadata.

Meta elements

Meta elements are HTML or XHTML elements used to provide structured metadata about a Web page. Such elements must be placed as tags in the head section of an HTML or XHTML document. Meta elements can be used to specify page description, keywords and any other metadata not provided through the other head elements and attributes. The meta element has four valid attributes: content, http-equiv, name and scheme. Of these, only content is a required attribute.

An example of the use of the meta element

In one form, meta elements can specify HTTP headers which should be sent before the actual content when the HTML page is served from Web server to client. For example:

" <meta http-equiv="Content-Type" content="text/html" /> "

This specifies that the page should be served with an HTTP header called 'Content-Type' that has a value 'text/html'. This is a typical use of the meta element, which specifies the document type so a client (browser or otherwise) knows what content type to render. In the general form, a meta element specifies name and associated content attributes describing aspects of the HTML page. For example:

" <meta name="keywords" content="wikipedia,encyclopedia" /> "

In this example, the meta element identifies itself as containing the 'keywords' relevant to the document, Wikipedia and encyclopedia. Meta tags can be used to indicate the location a business serves:

" <meta name="zipcode" content="45212,45208,45218" /> "

In this example, geographical information is given according to zip codes.