An identifier generating method according to the present invention has a
canonicalization process step of subjecting document data to a
canonicalization process to correct fluctuation of expression; and an
identifier generating step of, based on all or part of document data
having been subjected to the canonicalization process in the
canonicalization process step, generating an identifier uniquely
specifying the document data or part thereof. When the fluctuation of
expression is corrected by the canonicalization process, prior to the
generation of the identifier in this way, the XML documents or RDF
documents with the same meaning are transformed into documents in the
same expression, and the identical identifier can be generated for them
by a function of generating an identifier from a sequence of characters,
as typified by a one-way function.