A Lookup Link is required for all update, delete, and variable operations. The program looks for matches between source and target fields in order to update the appropriate records.
Lookup Link matches can be either exact matches (the default) or "fuzzy" matches based on scalar functions. An example of a scalar function is the SOUNDEX function, which could be applied to linked Lookup fields to find values that sound alike. Another scalar function supported is LEFT, where the comparison is based on the first 'x' number of characters rather than an exact match of the entire field.
Multi-segment keys are also supported by creating multiple Lookup Links.