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.

Duplicates, Nested query evaluation, Nested-iteration method, SQL, Syntax-directed SQL translation, Tuple identifiers, XRA
PDS Workshop
Centrum Wiskunde & Informatica, Amsterdam, The Netherlands

Verbrugge, N.Th. (1990). Duplicates and translation of nested SQL queries into XRA. In Lecture Notes in Computer Science/Lecture Notes in Artificial Intelligence (pp. 354–364). doi:10.1007/3-540-54132-2_66