What is the best way to enforce a 'subset' relationship with integrity constraints

Question

For example, given 3 tables:

• gastropod
• snail
• slug

and assuming we want to enforce that

1. every row in \'gastropod\

Answer 1

Ideally, I would make a single table "gastropod" with a "type" field, and then have views "gastropod" (selecting all fields except "type", with no "where" clause), "snail" (using a "where" clause to limit to type snail), and "slug" (using a "where" clause to limit to type slug). Exceptions may exist if one of the two types is much smaller and there are many fields relevant to only the smaller type, but for the most part making it different views from a single table will ensure the proper integrity constraints.