The pub_id link is for relating the usage of a given synonym to the publication in which it was used.
The is_current bit indicates whether the linked synonym is the current -official- symbol for the linked library.
Typically a synonym exists so that somebody querying the database with an obsolete name can find the object they are looking for under its current name. If the synonym has been used publicly and deliberately (e.g. in a paper), it my also be listed in reports as a synonym. If the synonym was not used deliberately (e.g., there was a typo which went public), then the is_internal bit may be set to "true" so that it is known that the synonym is "internal" and should be queryable but should not be listed in reports as a valid synonym.
Table contained -1 rows
|library_synonym_c1||Must be unique||Asc/Asc/Asc||synonym_id + library_id + pub_id|