Record de-duplication processes compare data in designated fields for the purpose of deleting duplicates and merging data from duplicated records in to a single record.

The DedupIgnore attribute can be set to "true" to prevent a field from ever being  included in a de-duplication process.

Example: the following element prevents the CreatedBy field from ever being evaluated when de-duplicating blog entry records.
<Relationship Id="CreatedBy" Name="Created By" TableId="Users" ReadOnly="true" NoOverride="ReadOnly" Multiple="false" DedupIgnore="true">