From what I've learned on relational theory I understand that every attribute of a relation is composed of a name and a domain, a type.
As Hugh Darwen define it (An introduction to Relational Database Theory, p40), to me a type (or domain) is a set a values.
In the integer set of possible values. I expect to find integers, nothing else. I guess I'm wrong then...
Tom.Thomson (6/30/2011)
For example a domain of unsigned integers range 0 to 255 contains the 256 integers 0...255 which are fully defined elements and the BOTTOM element about which nothing is known except that it a member of that domain;
If nothing is known about this element, does it really needs to exists ?