Conversely - Don't separate attributes when they are naturally connected. 34 Pear Ave. Combine tables as much as possible but make certain that there are no functions whose domain values are not keys. Keys A relation can often be viewed as a function from one subset of attributes to the remaining attributes. Actually, it does not define a function on all of CXI because all students haven't taken all courses.
Functions have to be single valued.
In order to view a relation as a function we have to find a set of attributes for the range such that no value in that set would ever be found in more than a single tuple. Such a set is called a key for the relation. 34 Pear Ave. Name by itself is not a key because, for example, there could be another C. Brown. StudentID and Name together constitute a key.