-Ordering of tuples in a relation r(R): The tuples are not considered to be ordered, even though they appear to be in the tabular form.
-Ordering of attributes in a relation schema R (and of values within each tuple): We will consider the attributes in R(A1, A2, ..., An) and the values in t= to be ordered.
(However, a more general alternative definition of relation does not require this ordering).
-Values in a tuple: All values are considered atomic (indivisible). A special null value is used to represent values that are unknown or inapplicable to certain tuples.
-Notation:
We refer to component values of a tuple t by t[Ai] = vi (the value of attribute Ai for tuple t).
Similarly, t[Au, Av, ..., Aw] refers to the subtuple of t containing the values of attributes Au, Av, ..., Aw, respectively
jim items answered the question on March 12, 2019 at 15:00
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