Principles for merging terms
Term Merges, Splits and Movements
Term merges
Terms are merged in cases where two terms have exactly the same meaning. Usually this situation arises when one term exists, and another wording of the same concept is added as a new term instead of as a synonym, either because a curator didn't find the old term or didn't know it meant the same thing.
When two terms are merged, e.g. term A and term B are merged into term A, the GO ID of term B is made a secondary GO ID, and the term string is made a synonym. Usually, the ID that has existed longer is used as the primary ID, but exceptions can be made; for example, the term string of the newer ID may be more correct or the definition may be better.
Secondary GO IDs are stored in the OBO flat file with the 'alt_id' tag.
Term splits
A term can be split if curators decide that it combines two or more concepts that should be represented by separate terms.
The standard procedure for splitting a term is to obsolete the original term and add a comment directing annotators to the new term.
Moving terms
Terms can be moved as long as the term's new position correctly reflects its relationships to other terms and moving the term does not imply a significant change in the meaning of the term. Terms should not, however, be moved between ontologies; only within the same ontology. If you need to move a term to a different ontology, first obsolete it and then create a new term in the other ontology.