Expressiveness of Eecient Semi-deterministic Choice Constructs ?

Recently, Abiteboul and Kanellakis introduced the notion of determinate query to describe database queries having the ability to create 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 considered. 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 eeciently.