1. A method for generating markup language to represent a calculation relationship among a plurality of facts, the method carried out by one or more computing devices, the method comprising: parsing markup language of an instance document containing the plurality of facts, wherein each fact comprises a value tagged according to one of a plurality of concepts, one or more relationships among the plurality of concepts is defined by markup language contained in a taxonomy document; based on the parsing, determining that at least two of the plurality of facts are in a calculation relationship with one another; generating markup language that represents the determined calculation relationship; and modifying the taxonomy document with the generated markup language.