Constraints ⇒ can't record conflicts

Relaxing constraints in the base variables allows for recording conflicting information. That means the DBMS can merge edits and keep the conflicting information in the merge result, allowing the users to fix it up as appropriate.

Example: key constraint

Imposing a functional dependency {X} --> {Y} prevents the database from recording conflicting information about the value of Y for a given value of X

Merging conflicts under OT

This addresses one of the issues some people have with Operational Transformation - when they hear that the merge of concurrent edits on the base variables is always defined and always succeeds they think the database has arbitarily "taken sides" and somehow taken it upon itself to resolve conflicts between users.

Perhaps they expect it to be like configuration management software like subversion or git where a merge conflict means a failure to perform the merge.

In actual fact the idea is to record the conflicts and highlight the inconsistencies in the data so the users can fix it themselves.

In a sense, under Operational Transformation a merge conflict doesn't produce a merge failure but rather a merge success with highlighted inconsistencies.

If you care about the accuracy of the data, then you want to record conflicting information and highlight it to the users so it is fixed properly. Recording what is actually known or thought to be known by the users, warts and all, is called data fidelity.