I'm more than happy to do the leg work to go through the questions currently tagged with db-api, and re-tag appropriately.
I removed the synonym.
I agree that schema-api is a better tag. I remember schema was used in questions about the database API not related with the schema API, or questions about the database. Maybe, using schema-api would help avoiding the tag is misused.
The excerpt for the tag wiki should suggest the related tags.