When there are multiple qualifier domains, you can specify a qualifier order to indicate how they are used during runtime lookups. The order of a qualifier varies from highest to lowest depending on the role of the qualifier in defining a more exact match. In Table 45-3, the state qualifier is probably given a higher order than the country qualifier because a matching state indicates a more precise match.

Domain value maps support hierarchical lookup. If you specify a qualifier value during a lookup and no exact match is found, then the lookup mechanism tries to find a more generalized match by setting the higher order qualifiers to empty quotes (""). It proceeds until a match is found, or until a the lookup is exhausted and no match is found. Figure 45-1 describes the steps of a hierarchical lookup performed for the following lookup (based on the values in Table 45-3):

State=Arkansas, Country=Canada, CityCode=KN_USA

In this example, the State qualifier has a qualifier order of 1 and the Country qualifier has a qualifier order of 2. As shown in Figure 45-1, the lookup mechanism sets the higher order qualifier State to the exact lookup value Arkansas and uses Canada|"" for the lower order qualifier Country.

If no match is found, the lookup mechanism sets the higher order qualifier State to a value of "" and sets the next higher qualifier Country to an exact value of Canada. If no match is found, the lookup mechanism sets the value of the previous higher order qualifier Country to a value of "". One matching row is found where CityCode is KN_USA and Kensington is returned as a value.

Table 45-4 provides a summary of these steps.