In reality, we have stumbled in to the world of nested relations – relations can be values. This is a major step for relational systems. There is much debate on how to proceed. Rather than attack those problems here, we just use the ALL value as a token representing these sets. Thinking of the ALL value as the corresponding set defines the semantics of the relational operators (e.g., equals and IN). The ALL string is for display. A new ALL() function generates the set associated with this value as in the examples above. ALL() applied to any other value returns NULL. This design may be eased by SQL3’s support for setvalued variables and domains.