I think they are talking about a junction table. I also think they're talking about a class table inheritance pattern, where you have a base table that stores

I think they are talking about a junction table. I also think they're talking about a class table inheritance pattern, where you have a base table that stores the data for the base/abstract class, then more tables to store the data for classes that extend the base class. You could use junction tables to model that relationship. http://en.wikipedia.org/wiki/Junction_table http://en.wikipedia.org/wiki/Junction_table