Semi-structured data includes forms of text or media that are not constrained to fixed formal notations or standardised values. Some fields may be simple data types such as numbers or short strings, as found in a standard database, but these are mixed with more complex values. Furthermore, even the simple fields may not be constrained by a simple schema, but may include ad-hoc fields. Accessing of semi-structured data may involve free-text search or by similarity. Examples include bibliographic databases and RDF.
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