Data matching can be either deterministic or probabilistic. In deterministic matching, either unique identifiers for each record are compared to determine a match or an exact comparison is used between fields. Unique identifiers can include national IDs, system IDs, and so on. This can include system IDs, national IDs, and so on. Deterministic matching is generally not completely reliable since in some cases no single field can provide a reliable match between two records. This is where probabilistic, or fuzzy, matching comes in. In probabilistic matching, several field values are compared between two records and each field is assigned a weight that indicates how closely the two field values match. The sum of the individual fields weights indicates the likelihood of a match between two records.