Duongthanhlong07
13-03-2010, 10:38
Consider an E/R diagram such as the one below, with a ternary relationship and arrows entering two of the related entity set, A and B.
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|---|'''''''''''''''''''/'''\'''''''''''''|---|
| A |<---------- ----------->| B |
|---|'''''''''''''''''''\'''/'''''''''''''|---|
'''''''''''''''''''''''''\'/
''''''''''''''''''''''''''|
''''''''''''''''''''''''''|
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''''''''''''''''''''''''| C |
''''''''''''''''''''''''|---|
There is a correct interpretation, which is that, given A and C entities, there is at most one related B entity, and, given B and C entities, there is at most one related A entity. There is also an incorrect interpretation "given a C entity, there is at most one related A entity and at most one related B entity".
a) Give an example of a relationship set that meets the correct interpretation of the diagram but does not meet the incorrect interpretation. You may use abstract entities, like a1, a2, b1, and so on, or you may give the entity sets a real interpretation(e.g., movies), and use actual values in the triples of your relationship set.
b) Does every relationship set that satisfies the incorrect interpretation of the correct interpretation? Justify your answer.
c) On the other hand, if the incorrect interpretation is what we want to say, there is another E/R diagram that says it.Draw this diagram.
Ai làm được giúp mình với nhé.Mình cần gấp lắm
'''''''''''''''''''''''''/'\
|---|'''''''''''''''''''/'''\'''''''''''''|---|
| A |<---------- ----------->| B |
|---|'''''''''''''''''''\'''/'''''''''''''|---|
'''''''''''''''''''''''''\'/
''''''''''''''''''''''''''|
''''''''''''''''''''''''''|
''''''''''''''''''''''''|---|
''''''''''''''''''''''''| C |
''''''''''''''''''''''''|---|
There is a correct interpretation, which is that, given A and C entities, there is at most one related B entity, and, given B and C entities, there is at most one related A entity. There is also an incorrect interpretation "given a C entity, there is at most one related A entity and at most one related B entity".
a) Give an example of a relationship set that meets the correct interpretation of the diagram but does not meet the incorrect interpretation. You may use abstract entities, like a1, a2, b1, and so on, or you may give the entity sets a real interpretation(e.g., movies), and use actual values in the triples of your relationship set.
b) Does every relationship set that satisfies the incorrect interpretation of the correct interpretation? Justify your answer.
c) On the other hand, if the incorrect interpretation is what we want to say, there is another E/R diagram that says it.Draw this diagram.
Ai làm được giúp mình với nhé.Mình cần gấp lắm