[知识点](What is metadata?转载)

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Metadata is data that describes other data. Meta is a prefix that in most information technology usages means "an underlying definition or description."

Metadata summarizes basic information about data, which can make finding and working with particular instances of data easier. For example, author, date created and date modified and file size are examples of very basic document metadata. Having the abilty to filter through that metadata makes it much easier for someone to locate a specific document.

In addition to document files, metadata is used for images, videos, spreadsheets and web pages. The use of metadata on web pages can be very important. Metadata for web pages contain descriptions of the page’s contents, as well as keywords linked to the content. These are usually expressed in the form of metatags. The metadata containing the web page’s description and summary is often displayed in search results by search engines, making its accuracy and details very important since it can determine whether a user decides to visit the site or not. Metatags are often evaluated by search engines to help decide a web page’s relevance, and were used as the key factor in determining position in a search until the late 1990s. The increase in search engine optimization (SEO) towards the end of the 1990s led to many websites “keyword stuffing” their metadata to trick search engines, making their websites seem more relevant than others. Since then search engines have reduced their reliance on metatags, though they are still factored in when indexing pages. Many search engines also try to halt web pages’ ability to thwart their system by regularly changing their criteria for rankings, with Google being notorious for frequently changing their highly-undisclosed ranking algorithms.

Metadata can be created manually, or by automated information processing. Manual creation tends to be more accurate, allowing the user to input any information they feel is relevant or needed to help describe the file. Automated metadata creation can be much more elementary, usually only displaying information such as file size, file extension, when the file was created and who created the file.

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