Key points are not available for this paper at this time.
In the interest of brevity we assume that the reader is familiar with the notion of a relational data base. In particular, we assume a familiarity with the work of Codd or Boyce and Chamberlin. The examples in this paper will be drawn from a data base which describes a department store and consists of three relations:
Chamberlin et al. (Wed,) studied this question.
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