An SQL extension supporting user viewpoints

  • Giuseppe Bellavia
  • Dario Maio
  • Stefano Rizzi
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 978)


In order to accomplish independence on the logical data organization, a relational DBMS must be capable of interpreting query language sentences which reference attributes belonging to different relations even if the necessary joins are not explicitly formulated (query inference problem). In this work we propose an SQL extension which supports concise formulation of queries through the dynamic definition of user viewpoints. User viewpoints are perspectives for accessing data; each user viewpoint defines a virtual derived relation (user viewpoint relation) which includes all those in the database scheme, each accessed by means of exactly one chain of system-activated equi-joins. Our approach to the definition of user viewpoint relations aims at reducing the global cost of query formulation, that is, the number of joins which must be explicitly written.


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  1. [1]
    G. Bellavia, D. Maio and S. Rizzi. Resolving the query inference problem by optimizing the query-formulation cost. Technical Report CIOC-C.N.R. n. 85 (1992).Google Scholar
  2. [2]
    G. Bellavia, D. Maio and S. Rizzi. Minimizing the cost of query formulation through User Viewpoint Relations. Atti del Secondo Convegno Nazionale su Sistemi Evoluti Per Basi Di Dati, Rimini, Italy, 141–159 (1994).Google Scholar
  3. [3]
    R. Fagin, A.O. Mendelzon and J.D. Ullman. A simplified universal relation assumption and its properties. ACM Trans. Database Syst. 7, 3, 343–360 (1982).CrossRefMathSciNetGoogle Scholar
  4. [4]
    W. Kent. Consequences of assuming a universal relation. ACM Trans. Database Syst. 6, 4, 539–556 (1981).CrossRefGoogle Scholar
  5. [5]
    A. Motro. Constructing queries from tokens. Proc. ACM SIGMOD Int. Conf. Management of Data. Washington D.C., 120–131 (1986).Google Scholar
  6. [6]
    E. Sciore. Query abbreviation in the entity-relationship data model. Information Syst. 19, 6, 491–511 (1994).CrossRefGoogle Scholar
  7. [7]
    J.A. Wald and P.G. Sorenson. Resolving the query inference problem using Steiner trees. ACM Trans. Database Syst. 9, 3, 348–368 (1984).CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 1995

Authors and Affiliations

  • Giuseppe Bellavia
    • 1
  • Dario Maio
    • 1
  • Stefano Rizzi
    • 1
  1. 1.DEIS-Facolta' di IngegneriaUniversita' di BolognaItalia

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