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Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.
Meta means "about," so metadata is "about data," or, more specifically, "information about data." There is metadata that describes the fields and formats of databases and data warehouses. There is metadata that describes documents and document elements, such as Web pages, research papers, and so on. And there are metadirectories that describe how information is organized in directories (see "Metadirectories" and "Directory Services".
An important feature of metadata is that it provides concise information about documents and data that improves searching. For example, compare searching entire sets of documents for keywords as opposed to searching descriptive indexes of those documents. A number of services have been defined for this. See "Search and Discovery Services."
Microsoft categorizes metadata as either technical or business oriented. Technical metadata supports developers and works like "glue" to link tools, applications, and systems into a solution. For example, it covers database structure, installed applications, and server systems. Business metadata makes the services of the enterprise environment more understandable to end users by describing business objects and processes to ease browsing, navigation, and querying of data.
Metadata for Database Management
Most people who are vaguely familiar with metadata think of database management systems. A database contains fields such as Name, Address, City, and so on. Metadata names these fields, describes the size of the fields, and may put restrictions on what can go in the field (for example, numbers only).
If you were to transfer a database file to someone without also giving them the metadata information, the file would appear to the recipient as a long string of characters. The metadata delineates in terms of the alignment of character blocks how the data should be extracted into fields and records. Therefore, metadata is information about how data is extracted, and how it may be transformed. It is also about indexing and creating pointers into data. Database design is all about defining metadata schemas.
The MDC (Meta Data Coalition) is a coalition of vendors and users with a common interest in defining, implementing, and evolving metadata interchange format standards. MDC manages the OIM (Open Information Model), a set of metadata specifications to facilitate sharing and reuse in the application development and data warehousing domains. The data model is based on industry standards such as UML, XML, and SQL.
Anyone who uses an advanced word processing program such as Microsoft Word can view and edit document metadata. For example, on the File menu, choose Properties. A dialog box appears that has general information about the document such as creation date, size, and so on. A Summary tab has metadata fields such as Title, Subject, Author, Manager, Company, Category, Keywords, and Comments. This information follows the definition for metadata: it is data about the data in the document and you can search for documents by searching this information.
Metadata takes the form of named element/value pairs. For example, the element City may have the value New York. A schema defines the vocabulary of a particular set of metadata (that is, element names and formatting rules). The metadata may be included with the document or stored in separate files. A schema is a separate file that is referenced from the document.
Different industries usually choose to define schemas that fit their needs, but several standard global schemas have been developed. An important aspect of metadata is that it be machine readable, meaning that it is in a form that applications can access and use without human intervention. The Dublin Core metadata scheme defines a standard set of elements that can be used across a broad set of documents. Library researchers played a big part in defining the Dublin Core, which should give you an idea of how and why it is used. The Dublin Core provides the basis for a standardized electronic card catalog for electronic documents.
One of the best examples of the use of metadata is XML, which defines metadata in DTDs (Document Type Definition) files. XML provides a universal way to exchange business information. Various industries have created their own XML standards to represent information specific to their industry. See "XML (Extensible Markup Language)" for more information. Also see "Electronic Commerce" for a discussion of how XML is used for business transactions.
Metadata Recommendations and Standards
A number of vendors, organizations, consortiums, international standards bodies, and working groups are developing metadata recommendations and standards. Some examples are given here.
Copyright (c) 2001 Tom Sheldon and Big Sur Multimedia.