Formal Public Identifier. A text string that serves as a structured citation to an SGML object such as an entity, a DTD, or an element. An FPI includes the name of its owner, the class of objects to which the associated item belongs (e.g., DTD, entity), an arbitrary description of the object, its language, and, optionally, its version. Public identifiers contrast with system identifiers that identify an SGML object by citing a system-specific characteristic, such as a URL or a file name that physically locates the object in a file storage system.