about relational algebra
- To: mathgroup at smc.vnet.net
- Subject: [mg33359] about relational algebra
- From: zcdy2002 at hotmail.com (zcdy)
- Date: Sun, 17 Mar 2002 05:33:11 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
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. zcdy