The interface to the inventory system works by mapping between fields in the inventory data and those in ST data, in order to find inventory records that can reveal information missing from ST records. The fields currently provided by the interface include barcode, machine name, subscription code, location which have equivalent fields in the inventory system. Whatever data is provided by the inventory system in use is used, which is determined by the version of ST in use (MFCF vs CSCF). As of 2015, the two happen to be the same.
In addition to ST fields, there are some inventory fields that don't have an equivalent in ST, so they are given names prefixed "X-" to identify them as such. They are the inventory primary key X-pkey and (optional) MFCF support level X-support. In practice, these names are only seen in error messages in the record update and record display pages when ambiguous inventory records are found.