1. A computer-implemented method for constructing a change database, comprising the steps of: a. accessing from a processor a reference database, wherein the reference database comprises, for a data element corresponding to an identifier, a first value and a second value, and a first time period corresponding to a first change between the first value and the second value; b. calculating a first change indicator representing a significance of the first change; and c. writing from the processor to the change database a first record for the first change indicator, the first change record comprising an identifier field, a first time period field, and a first change indicator field.