The PRISMA/DB system contains a parser to translate the database language SQL into eXtended Relational Algebra (XRA). The early definition of XRA, which has a multi-set semantics, proves inadequate for translating SQL according to its nested-iteration semantics. The prime cause is that no distinction is made between original and generated duplicate tuples during nested query handling. To achieve a correct translation, tuple identifiers were introduced into XRA and the system