Just wanted to add a link to a resource that most authors refer to as not (fully) available online.
A Relational Model of Data for Large Shared Data Banks by E. F. Codd
http://www.acm.org/classics/nov95/toc.html
I think this is the full text.
For those who are interested.
Frank
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Frank Kalis
Microsoft SQL Server MVP
Webmaster: http://www.insidesql.org/blogs
My blog: http://www.insidesql.org/blogs/frankkalis/[/url]