1. A method of identifying matches between a sample data record and a plurality of enrolled data records, the method comprising: a) Defining an implicit or explicit plurality of reference positions within a data record; b) Defining an implicit or explicit key pattern related to each said reference position; c) Combining data from said key pattern into a key value; d) Associating a list of record identifiers with each said key value for at least some of said reference positions; e) For enrolment of a data record, defining an implicit or explicit enrolment mask associated with said reference positions and adding a record identifier for said data record to said list of record identifiers associated with the key value determined by combining data from said key pattern for at least some of said reference positions where indicated by said associated enrolment mask; For seeking a match for a sample data record, defining an implicit or explicit sample mask associated with said reference positions and extracting said list of record identifiers associated with the key value determined by combining key patterns for at least some of said reference positions where permitted by said associated sample mask; g) Determining the number of occurrences of at least one record identifier in the lists associated with said key values for at least some of said reference positions where permitted by said associated sample mask; and h) Identifying a given enrolled data record as being a match or possible match with the sample data record if said number of occurrences is at least some required number.