Duplicates and translation of nested SQL queries into XRA

  • N. Th. Verbrugge
PRISMA Contributions
Part of the Lecture Notes in Computer Science book series (LNCS, volume 503)


The PRISMA/DB system1 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 SQL XRA nested query evaluation nested-iteration method tuple identifiers syntax-directed SQL translation 


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Copyright information

© Springer-Verlag Berlin Heidelberg 1991

Authors and Affiliations

  • N. Th. Verbrugge
    • 1
  1. 1.CWIAmsterdam

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