The VariableInstance object maps a variable to its associated columns in the VDATA virtual table and the VariableInstance.FullName property corresponds to the name of the column. There is one VariableInstance object for each column in the VDATA virtual table. However, there may be more than one column in the virtual table for a single variable. For example, a categorical variable that has one Other Specify category, would typically be represented by three VariableInstance objects. The first represents the column that holds the responses to the category list, the second represents the helper field that stores the open-ended responses, and the third represents the helper field that stores the coded responses.

The Document.Variables property returns a Variables collection that is a flat list of all of the VariableInstance objects in the top-level virtual table, which is VDATA when the case data is being represented in a non-hierarchical form.