Double List Attributes are used to relate values of two different attributes, where for certain values of one attribute, only a limited list of values of the second attribute are allowed.
For example, suppose you are building an Auditor project and you want to check that the referring doctor (as entered) has a valid referring doctor code (as entered). You can build a Double List Attribute where the first attribute is RefDr, the second attribute is RefDrCode. You define a list of referring doctors and for each referring doctor a list of valid refreeing doctor codes. You can then add a rule that flags cases where the referring doctor is on the list, but the referring doctor code is not correct.
To define a Double List Attribute, select the first attribute (ward in the example above) in the Attribute Editor. Then choose Edit|Add double list… and follow the prompts.