Help will greatly be appreciated Consider the E/R diagram above, and suppose tha
ID: 3544083 • Letter: H
Question
Help will greatly be appreciated
Consider the E/R diagram above, and suppose that al and a2 arc entities of entity set A, bl and b2 arc entities of set B, and cl and c2 arc entities of set C. The arrows limit the possible relationship sets for R and S. Describe the limitations on these relationship sets. Then, confirm your understanding by identifying which of the following relationships sets for R and S arc possible according to the diagram. R = {(al ,bl)}, S = {(b2,c2)} R = {(al,bl), (a2,bl)}; S = {(bl,c2)} R = {}; S = {(bl,c2), (b2,c2)} R = {(al ,b2), (al.bl), (a2,bl)}; S = {(bl,c2), (b2,cl)}Explanation / Answer
In this diagram, one to many relationships are present between A and B, and B and C.
In all options, lets consider one by one.
Option a) is possible because, for a value a1 that belongs to A, there is only one value b1. For one value b2 that belongs to B, there is only one value of C that us c2.
Option b) is not possible because, for 2 different values of A(a1 and a2), there is single value of B.
Option c) is not possible because, R cannot be null because there is a primary key attribute present, that can never be null. For 2 values of B(b1, b2), only single value c2 is present which is not possible in one to many relationship.
Option d) is not possible because there is many to one relation is present. For a1, and a2, single value b2 is mapped. Hence, this is also not possible.
Conclusion: Only Option a) is possible.
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