Answer 1

Not quite sure what you're asking for here. What do you mean by "derived attribute"?

If it is simply to derive an "AGE" column in a select statement, then you can just use the DATEDIFF function and specify the years between the DOB column and GetDate().

If you're looking for a "derived table", that's really nothing more than joining to a parenthesized "Select" statement. Frankly, in most cases you're better off using straight joins.