MathGroup Archive 2002

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about relational algebra

  • To: mathgroup at
  • Subject: [mg33359] about relational algebra
  • From: zcdy2002 at (zcdy)
  • Date: Sun, 17 Mar 2002 05:33:11 -0500 (EST)
  • Sender: owner-wri-mathgroup at

Show that the Selection Project Cross-product Union algebra,in which
selection operators with negation in the formulas are permitted, can't
simulate the difference operator.

Any idea of the above excise is greatly appreciated.
Thank you very much.

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