Talk:Tuple relational calculus

In the current page: Along with the tuple calculus Codd also introduced the domain calculus which is closer to first-order logic and showed that these two calculi (and the relational algebra) are equivalent in expressive power

However, to my knowledge, Codd only proposed Relational Algebra (RA) and Tuple Relational Calculus (TRC), but not Domain Relational Calculus (DRC). DRC was proposed by Michel Lacroix and Alain Pirotte in VLDB 1977. (Ref: http://www.informatik.uni-trier.de/~ley/db/conf/vldb/LacroixP77.html, and also see Ramakrishnan's "Database Management Systems", 3rd ed., pp129). I've fixed that in the DRC wikipage (also provided the reference of Codd's article proving the equivalence of RA and TRC).

(I'm relatively new to Wikipedia, so I'm not sure what the conventions are - please excuse)

The link to Linda above either needs to point to something like LindaCoordinationLanguage or the page for Linda needs to contain information about the language. Unfortunately, I don't know enough about Linda to even start. Sorry.


 * You are right. But Linda is not really a tuple calculus at all, but rather a process description language. Unless someone comes along with a good justification I suggest we remove it. -- Jan Hidders 15:35 29 May 2003 (UTC)

The linking of calculus is not really justified since calculus is used in a different meaning here than in the article. If no-one objects I will remove it. -- Jan Hidders 12:27, 13 Apr 2004 (UTC)


 * I think the link should point to Predicate calculus] or [[Propositional calculus instead. —Preceding unsigned comment added by 75.142.63.207 (talk) 23:59, 11 January 2011 (UTC)

A list of prerequist reading might make this article a little easier to understand.

Safe Queries
The algorithm given for determining if a query is a "safe query" seems unlikely to be correct. It makes no distinction between existential and universal quantifiers. (Assuming my browser is rendering the equations correctly...) Under this definition a query would remain "safe" if you change any of its quantifiers from existential to universal or from universal to existential. This is in contrast to every other version of the definition I have read, where the conditions for existentials and universals always differ in some way. QuasiQuote (talk) 22:31, 8 April 2011 (UTC)