Curator Guide: Merge Split Move
Term Merges, Splits and Movements
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.
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 to add 'consider' tags for the old term ID to all new terms. It's also good practice to add a comment explaining why the term was split, e.g.:
id: GO:0004327 name: formaldehyde dehydrogenase (glutathione) activity namespace: molecular_function def: "OBSOLETE. Catalysis of the reaction: formaldehyde + glutathione + NAD+ = S-formylglutathione + NADH + H+." [EC:22.214.171.124] comment: This term was made obsolete because it was derived from an EC entry (126.96.36.199) that has since been split into two entries. subset: gosubset_prok xref: UM-BBD_enzymeID:e0028 is_obsolete: true consider: GO:0051903 consider: GO:0051907
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.