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Metadata is "data about data".〔http://www.merriam-webster.com/dictionary/metadata〕 Two types of metadata exist: structural metadata and descriptive metadata. Structural metadata is data about the containers of data. Descriptive metadata uses individual instances of application data or the data content. Metadata was traditionally in the card catalogs of libraries. As information has become increasingly digital, metadata is also used to describe digital data using metadata standards specific to a particular discipline. Describing the contents and context of data or data files increases their usefulness. For example, a web page may include metadata specifying what language the page is written in, what tools were used to create it, and where to find more information about the subject; this metadata can automatically improve the reader's experience. The main purpose of metadata is to facilitate in the discovery of relevant information, more often classified as resource discovery. Metadata also helps organize electronic resources, provide digital identification, and helps support archiving and preservation of the resource. Metadata assists in resource discovery by "allowing resources to be found by relevant criteria, identifying resources, bringing similar resources together, distinguishing dissimilar resources, and giving location information."〔 == Definition == Metadata means "data about data". Although the "meta" prefix (from the Greek preposition and prefix μετά-) means "after" or "beyond", it is used to mean "about" in epistemology. Metadata is defined as the data providing information about one or more aspects of the data, it is used to summarize basic information about data which can make tracking and working with specific data easier. Some examples include: * Means of creation of the data * Purpose of the data * Time and date of creation * Creator or author of the data * Location on a computer network where the data was created * Standards used * File size For example, a digital image may include metadata that describe how large the picture is, the color depth, the image resolution, when the image was created, and other data.〔(【引用サイトリンク】title=ADEO Imaging: TIFF Metadata )〕 A text document's metadata may contain information about how long the document is, who the author is, when the document was written, and a short summary of the document. Metadata within web pages can also contain descriptions of page content, as well as key words linked to the content. These links are often called "Metatags", which were used as the primary factor in determining order for a web search until the late 1990s.〔 The reliance of metatags in web searches was decreased in the late 1990s because of what can be referred to as "keyword stuffing".〔 Metatags were being largely misused to trick search engines into thinking some websites had more relevance in the search than they really did.〔 Metadata is data. As such, metadata can be stored and managed in a database, often called a metadata registry or metadata repository.〔Hüner, K.; Otto, B.; Österle, H.: Collaborative management of business metadata, in: International Journal of Information Management, 2011〕 However, without context and a point of reference, it might be impossible to identify metadata just by looking at them.〔(【引用サイトリンク】title=Metadata Standards And Metadata Registries: An Overview )〕 For example: by itself, a database containing several numbers, all 13 digits long could be the results of calculations or a list of numbers to plug into an equation - without any other context, the numbers themselves can be perceived as the data. But if given the context that this database is a log of a book collection, those 13-digit numbers may now be identified as ISBNs - information that refers to the book, but is not itself the information within the book. The term "metadata" was coined in 1968 by Philip Bagley, in his book "Extension of Programming Language Concepts" where it is clear that he uses the term in the ISO 11179 "traditional" sense, which is "structural metadata" i.e. "data about the containers of data"; rather than the alternate sense "content about individual instances of data content" or metacontent, the type of data usually found in library catalogues.〔"The notion of "metadata" introduced by Bagley". 〕 Since then the fields of information management, information science, information technology, librarianship, and GIS have widely adopted the term. In these fields the word ''metadata'' is defined as "data about data".〔 〕 While this is the generally accepted definition, various disciplines have adopted their own more specific explanation and uses of the term. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「metadata」の詳細全文を読む スポンサード リンク
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