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An XML database is a data persistence software system that allows data to be specified, and sometimes stored, in XML format. These data can be queried, transformed, exported and returned to a calling system. XML databases are a flavor of document-oriented databases which are in turn a category of NoSQL database (meaning Not (only) SQL). == Rationale for XML in databases == There are a number of reasons to directly specify data in XML or other document formats such as JSON. For XML in particular, they include: * An enterprise may have a lot of XML in an existing standard format * Data may need to be exposed or ingested as XML, so using another format such as relational forces double-modeling of the data * XML is very well suited to sparse data, deeply nested data and mixed content (such as text with embedded markup tags) * XML is human readable whereas relational tables require expertise to access * Metadata is often available as XML * Semantic web data is available as RDF/XML Steve O'Connell gives one reason for the use of XML in databases: the increasingly common use of XML for data transport, which has meant that "data is extracted from databases and put into XML documents and vice-versa". It may prove more efficient (in terms of conversion costs) and easier to store the data in XML format. In content-based applications, the ability of the native XML database also minimizes the need for extraction or entry of metadata to support searching and navigation. 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「XML database」の詳細全文を読む スポンサード リンク
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