Express key matching can be a useful tool for reducing the number of compares performed and thereby improving execution speed in dataflows that use an Interflow Match or Intraflow Match stage. If two records have an exact match on the express key, the candidate is considered a 100% match and no further matching attempts are made. If two records do not match on an express key value, they are compared using the rules-based method. However, a loose express key results in many false positive matches.
To determine whether a candidate was matched using an express key, look at the value of the ExpressKeyIdentified field, which is either Y for a match or N for no match. Note that suspect records always have an ExpressKeyIdentified value of N.