How ever what would happen further down the line when it comes to implementing the design and if I decide not to roll up the subtypes to the supertype. That would leave me with 4 tables (organisation, charity, company and trust) and the same column "registered address" defined in two separate tables.
Physical implementation is a different animal :-)
I would probably implement this at the Supertype level, meaning I'll create a single ORGANIZATIONS table to describe Companies, Charities and Trusts. This table will include both primary_address and registered_address columns.
So... where are the subtypes? I'll include an organization_type column in ORGANIZATIONS table to document what kind of organization is being described in each row.
Does it makes sense?
Pablo (Paul) Berzukov
Author of Understanding Database Administration
available at Amazon and other bookstores.Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.