My goto example is phone numbers; typically you store the whole thing, but what if you want to do analysis on zones? You'd just extract the zone, not redesign

My goto example is phone numbers; typically you store the whole thing, but what if you want to do analysis on zones? You'd just extract the zone, not redesign your schema and rebuild the database. You could argue that things like LIKE and SUBSTR etc are not really part of the relational model at all, but merely application code leaking into the SQL for convenience. Therefore, you shouldn't expect / demand that the results are a formal relation.