The Role and Function of Metadata
Metadata is data about data. When data is stored in some sort of structured format, metadata can describe the format and content of this data store. Metadata is a vital element in many computing applications with data elements. If a program is accessing data stored at some location external to the program itself, the code may be able to access and use that data, providing it can first access the metadata.
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Concept
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As well as describing other data, metadata is itself also data. The content of metadata normally is comprised of a description or indication of the characteristics of a particular set of data. For example, in a database with a table containing customer records for a commercial company, the metadata for the table would outline the structures, fields and relationships within the customer records. Metadata can also describe information about a single document, such as a Web page, providing the Web browser with the information it needs to render the page content effectively for user viewing.
Function
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The function of metadata is usually to facilitate use of a set of data. For example, if a computer program is connecting to a database to query it for information, the metadata could provide it with information regarding the content of the database, including the tables, fields and data types included. In websites, metadata is listed within "meta" elements, which provide everything the browser needs to know regarding the media content and information formats in a page. In general, metadata exists to help make sense of the data to which it refers.
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Definition
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Definitions of metadata relate to the context of a project, as well as the technologies involved. The content of metadata can be outlined in a schema. For example, XML Schema definitions appear within XSD documents. An XSD describes a set of structures and elements within XML data. In this sense, an XML Schema definition declares the metadata for a set of data stored within XML. In general, a schema for metadata will explain the elements in the data, what they contain and what their purpose is. Since the content of metadata is also data, metadata definitions such as XSDs can also be described using a further level of metadata.
Considerations
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There are cases in which metadata is essential in order to make use of data. Many programming languages such as Java provide standard resources for accessing metadata associated with databases. Once an application processes metadata, it can then create queries suited to the structure and content of the data in question. Conversely, metadata declarations such as XML Schema documents can help developers to check whether a data store they are working on is formatted and structured in a way that observes the metadata rules.
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References
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