Expressiveness of E cient Semi Deterministic Choice Constructs

Recently Abiteboul and Kanellakis introduced the notion of determinate query to describe database queries having the ability to cre ate new domain elements As there are no natural determinate complete query languages known more restrictive the constructive queries and more general the semi deterministic queries notions of query were con sidered Here we show that the advantage of the second approach over the rst is not so much in increased expressiveness but in the ability of expressing queries more e ciently