1. A data processing method in a computer for responding to processing requests with cached data, comprising the steps of: preparing a first processing request, wherein preparing the first processing request comprises: canonicalizing a first data file with the use of a template that complies with predetermined canonicalization rules to create a first canonicalized data file; including the first canonicalized data file with the first processing request; including canonicalization indication information indicating that the first data file has been canonicalized in the header of the first processing request; transmitting the first processing request to a server; caching data for responding to the first processing request in a cache table stored in memory by using the first canonicalized data file included in the first processing request as a key based on the header of the first processing request including canonicalization indication information indicating that the first data file has been canonicalized; preparing a second processing request, wherein preparing the second processing request comprises: canonicalizing a second data file with the use of the template that complies with the predetermined canonicalization rules; including the second canonicalized data file with the second processing request; including canonicalization indication information indicating that the second data file has been canonicalized in the header of the second processing request; transmitting the second processing request to the server; responding to a second processing request made after caching the data for responding to the first processing request, wherein the second processing request includes a second canonicalized data file, wherein responding to the second processing request comprises: searching for the data cached in the cache table by using the canonicalized data file included in the second processing request as a key, wherein the first canonicalized data file matches the second canonicalized data file; and responding to the second processing request with the cached data.