Metadata
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- Metadata is also a U.S. trademark of The Metadata Company
Metadata (Greek: meta-+data "information") means data about data. While this definition is commonly offered, it is also commonly not helpful. An 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.
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Uses
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 how they are known in some countries.
For examples of metadata for an audio CD, look at the MusicBrainz project, or AMG's All Music Guide. Similarly, MP3 files have metadata tags in a format called ID3.
Metadata is more properly called ontology or schema when it is structured into a hierarchical arrangements. Both terms describe “what exists” for some purpose or to enable some action. For instance, the arrangement of subject headings in a library catalog serves as not only a guide to finding books on a particular subject in the stacks, but also as a guide to what subjects “exist” in the library’s own ontology and how the more specialized topics are related to or derived from the more general subject headings.
Types
Data warehouse metadata
Kimball[[#References|]] lists the following types of metadata in a data warehouse (See also [1] (http://www.fortunecity.com/skyscraper/oracle/699/orahtml/dbmsmag/9803d05.html)):
- source system metadata
- source specifications — such as repositories, source schemas &c.
- source descriptive information — such as ownership descriptions, update frequencies, legal limitations, access methods &c.
- process information — such as job schedules, extraction code &c.
- data staging metadata
- data acquisition information — such as data transmission scheduling and results, file usage;
- dimension table management — such as definitions of dimensions, surrogate key assignments &c.
- transformation and aggregation — such as data enhancement and mapping, DBMS load scripts, aggregate definitions &c.
- audit, job logs and documentation — such as data lineage records, data transform logs &c.
- DBMS metadata — such as
- DMBS system table contents,
- processing hints &c
- front room metadata — such as
- descriptions for columns
- network security data
- favorite web sites &c.
File system metadata
Nearly all file systems keep metadata about files out-of-band. Some systems keep metadata in directory entries; others in specialized structure like inodes or even in the name of a file. Metadata can range from simple timestamps, mode bits, and other special-purpose information used by the implementation itself, to icons and free-text comments, to arbitrary attribute-value pairs.
With more complex and open-ended metadata, it becomes useful to search for files based on the metadata contents. The Unix find utility was an early example, although inefficient when scanning hundreds of thousands of files on a modern computer system. Apple Computer's current version of its Mac OS X operating system (Tiger) supports cataloging and searching for file metadata through a feature known as Spotlight. Microsoft Windows (Longhorn) is expected to include a similar functionality via the WinFS file system.
Program metadata
Most executable file formats include metadata describing issues that need to be considered by the runtime or operating system when executing the program.
In DOS, the COM file format does not, but the EXE file format does, and the latter is expanded for Windows to the PE format.
In the Microsoft .NET executable format, extra metadata is included to allow reflection at runtime.
For a list of executable formats, see object file.
See also
- Dublin Core
- ID3
- APEv2 tag
- Exif
- IPTC (image meta-data)
- Kendra initiative
- m:Edit metadata
- meta tags
- MOF
- RDF
- The Semantic Web
- Topic maps
- XML
- Magic number (programming)
- metatable
- GNUBrain
External links
- Metadata in the World Wide Web (http://www.cs.njit.edu/~galnares/Metadata.html)
- "Enterprise Elements Metadata Repository" (http://www.enterprise-elements.com) - A COTS tool that stores and displays data and metadata
- "Metacrap" (http://www.well.com/~doctorow/metacrap.htm) - An opinion on the limitations of metadata on the internet
- Research Paper on Metadata Communications (http://www.rtodd.com/speaking/2004/IPCC/Metadata%20Communications%20v4.pdf)
- A review of Mac OS X v. 10.4's new metadata implementations (http://arstechnica.com/reviews/os/macosx-10.4.ars/6)
- Meta Meta Data Data (http://www.fortunecity.com/skyscraper/oracle/699/orahtml/dbmsmag/9803d05.html) - Article by Ralph Kimball
- Metadatarisk.org (http://www.metadatarisk.org)- Information on the Risks of Document Metadata
References
Template:Footnote Ralph Kimball, The Data Warehouse Lifecycle Toolkit, Wiley, 1998
Blog link
- Enterprise Metadata (http://www.rtodd.com/blog/)cs:Metadata