““Any domain knowledge is not a plain set of relations, it is whole hierarchy of relations. And not surprisingly only a minority of relations are leaves of this hierarchy, typically a majority of relations adopt other relations as domains. We have a representation: relation → table; domain → attribute. But a table can not adopt another table as an attribute! Therefore, we can not represent our domain knowledge in terms of tables. There simply is no room for relations between relations. Though, we can represent SOME relations””
