1. A method, comprising: storing a collection of digital information in a first file; storing a query expression in a cache file, wherein the query expression specifies a subset of digital information to be retrieved from the collection of digital information in the first file; retrieving the subset of digital information from the first file, wherein said retrieving comprises parsing the collection of digital information in the first file according to the query expression; storing a currency token in association with the cache file, wherein the currency token indicates whether the cache file is current; storing the retrieved subset of the collection of digital information in the cache file in association with the stored query expression; and wherein the currency token includes an attribute of the first file, and wherein the attribute describes the first file at a time when the collection of digital information stored in the first file is parsed to generate the subset of the collection of digital information which is stored in the cache file.