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Metadata is data about data. A good example is a library catalog card, which contains data about the nature and location of a book: it is data about the data in the book referred to by the card.

The content combined with its metadata is often called a content package.

Table of contents
1 Uses
2 Filesystem metadata
3 See also


Metadata has become important on the World Wide Web because of the need to find useful information from the mass of information available. Manually-created metadata adds value because it ensures consistency. If one webpage about a topic contains a word or phrase, then all webpages about that topic should contain that same word. It also ensures variety, so that if one topic has two names, each of these names will be used. For example, an article about sports utility vehicles would also be given the metadata keywords '4 wheel drives', '4WDs' and 'four wheel drives', as this is what they are known as in Australia.

For an example of Metadata for an Audio CD look at the MusicBrainz project, or the Musicbrainz Metadata Initiative. Similarly, MP3 files have metadata tags in a format called ID3.

Metadata is more properly called Ontology (computer science) or schema when it is of broad or narrow utility. Both terms describe "what exists" for some purpose or to enable some action. For instance, the library card's minimal schema enables a user to determine quickly whether they wish to look at the book, and if so, how to find it quickly.

Filesystem metadata

Some file systems keep metadata about files out-of-band while others keep it in the filename or inside the file. Examples of metadata are the filetype, abstracts, iconss. Examples of filesystems that keep metadata separate but related to the actual data are the BeFS of BeOS, HPFS of OS/2, HFS/HFS+ of Mac OS, ReiserFS of Linux, and NTFS of Windows.

The next major upgrades to Microsoft Windows and Mac OS X, "Longhorn" and "Tiger" respectively, are expected to integrate an SQL server engine into their filesystems, allowing greater flexibility in the maintenance and searching of metadata.

See also

Metadata® is the name of a US corporation and a registered trademark in the United States.

In the early summer of 1969, Jack E. Myers coined the term "metadata" and first used it in print in a 1973 product brochure. He intentionally designed it to be a term with no particular meaning. A data and publication search at that time did not discover any prior use either of the word "metadata" or "meta data." The word Metadata® was registered in 1986 as a trademark (U.S. Trademark Registration No. 1,409,206) belonging to The Metadata Company. The trademark was granted "incontestable" status in 1991. Metadata is a proprietary mark which stands for The Metadata Company.

The Metadata Company has attempted to threaten people legally into not using the word "metadata" in the generic sense. Many people believe that due to the widespread use of the word "metadata" in the generic sense as "data about data", it is likely that the "Metadata" trademark has entered the public domain by becoming a general term. This was the legal opinion expressed by the Office of the Solicitor of the United States Department of the Interior to the Federal Geographic Data Committee when the latter was threatened by Metadata's lawyers for its use of the word "metadata" in a generic sense. However, no judge has as yet ruled the trademark invalid.