Patent US 6,098,071

A document difference extraction method and apparatus which is used for extracting the difference between structured documents properly meeting the sense of a document editor taking the logical meaning and structure of the structured documents into consideration. Structured documents are edited and stored in a memory unit by a document editing program. With reference to a comparison criterion set for the logical structure of each structured document before and after edition, the logical structure of the structural documents before and after edition read from the memory unit is analyzed by a structured document parsing program, and the difference between the structured documents is extracted by a structured document difference extraction program in such a manner as to satisfy the comparison criterion in accordance with the result of parsing. The comparison criterion assumes the form of a table containing a plurality of tags representing logical structures and types of tags for the comparison criterion. The tag types for comparison criterion include tags having contents which are compared only when the particular tags are coincident with each other, tags having contents which are ignored at the time of comparison, a set of tags having the same logical meaning, and a set of tags having contents which are not compared with each other.