We investigate how the standard database query language SQL can be ext
ended to deal with the newly emerging trends of complex objects and ob
ject orientation. Our main concern is to extend SQL as naturally as po
ssible, rather than to redesign SQL into ''yet another'' object-orient
ed query language. We achieve this goal through a faithful mapping fro
m a complete object-oriented database model, compatible with recent pr
oposals in the held, to the nested relational database model, which is
widely accepted as a natural extension of the relational database mod
el on which standard SQL is based. We provide formal definitions of sy
ntax and semantics. We also review related research and situate our wo
rk into it.