The MDM assigns a unique value to each unique element full name in the MDM Document. The unique values are called mapped category values (sometimes shortened to mapped values). Element full names must be unique within a question, but the same element full name can be used in different questions. For example, categories called Yes and No can be used in several questions, and will have the same mapped value in each one.

The MDM allocates mapped values to analysis elements as well as to category elements. It is not possible to predict which values the MDM will allocate to any particular element, but mapped values that have already been allocated in existing .mdd files will be preserved.

You can use the CategoryMap.Add method to manually assign values to particular categories. These values will then be preserved when the MDM does the automatic allocations or you use the CategoryMap.AutoAssignValues method. The CategoryMap.Add method is useful when it is imperative that a particular mapped value is assigned to a particular category.

It is generally preferable to use category names rather than category values when querying and filtering case data.