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+3 votes
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Which of the following statements is false about weak entity set?

  1. Weak entities can be deleted automatically when their strong entity is deleted
  2. Weak entity set avoids the data duplication and consequent possible inconsistencies caused by duplicating the key of the string entity
  3. A weak entity set has no primary keys unless attributes of the strong entity set on which it depends are included
  4. Tuples in a weak entity set are not partitioned according to their relationship with tuples with a strong entity set
in Databases by Veteran (100k points)
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2 Answers

+3 votes
Best answer
We have weak entities for several reasons:
  •  We want to avoid the data duplication and consequent possible inconsistencies caused by duplicating the key of the strong entity.
  •  Weak entities reect the logical structure of an entity being dependent on another entity.
  •  Weak entities can be deleted automaticallywhen their strong entity is deleted.
  •  Weak entities can be stored physically with their strong entities.

D is incorrect statement. so the choice will be D.

 

by (287 points)
selected by
+1 vote
Weak entity set is one which does not have any primary key..

(a) is true because weak entity set does not have any existence without strong entity in database. For every entry of weak entity we have corresponding strong entity entry in DB.

let we have employee(strong) and family(weak) as entity sets.

(b)can be false because weak entity set does not have their own primary key so it can have duplication and inconsistency problem that's why it needs strong entity always and hence called as dependent entity.

(c) is obviously true

(d) is true because there is no relationship of tuple partitioning b/w weak and strong entity sets
by Loyal (8.4k points)
0
B is correct because we need strong entity to uniquely identify weak entity, the value of weak entity can be repeated and there may be the duplicate value of foreign key
0

Not sure about B, but D is definitely false.. http://web.cs.ucla.edu/classes/fall04/cs143/solutions/chap2.pdf, question 2.9

 

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