Ordering of tuples in a Relation : The tuples are not considered to be in order, even though they appear to be in the tabular form. The Ordering of attributes in a relation schema R and of values within each tuples - We consider the attributes in R(A1, A2, .., An) and the values in t=<v1, v2, .., vn> to be in order. Values in a tuple : All values are considered to be indivisible (atomic). A special null value is used to represent values that are unknown or not applicable to certain tuples.
