Margaret has a problem. A database designer, Margaret is responsible for creating a database that the American Association of Retired Persons (AARP) will use to keep track of its members and other people involved with the organization. However, because the people in the database can participate in the organization in many different ways (or might not be actively involved at all), Margaret's database has several empty subtypes, and she's not sure how to deal with them. She's still working on the database design, and she wants to avoid the performance and coding problems that can result from a badly designed table.

Mar...