Sophisticated end users
Naïve users.
Stand-alone users.
Casual end user
External
Internal
Physical
Conceptual
Passive and active
Total and partial
Simple and Complex
All of the above
All the tuples of R1
All the tuples of R2
All the tuples of R1 and R2
All the tuples of R1 and R2 which have common columns
Attribute
Degree.
Tuple.
Domain.