Dbms #weak-entity

Question

Which of the following statements are true for weak entity sets:

1. A weak entity set cannot have a primary key.

2. A weak entity set must have a local attribute in primary key.

3. A weak entity must borrow an attribute from another entity sey to form a primary key.

a) 1 and 2

b) 2 and 3

c) 3 only

d) none of these

Comments

This link might help you
http://www.ques10.com/p/9630/explain-weak-entity-set-with-suitable-example-1/

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hi arnab ...i think all options are correct here means all 3 statments are correct.....if i am wrong ..pls tell the statment which is wrong..

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By definition,
a entity set that does not have a primary key is called weak entity.
It takes help from other entity to form a primary key.
So i think All are correct.

Answer 1

i think all options are correct here ...

1) entity has no primary key that's why its called as weak entity.....so true..

2)i think 2nd is also correct because...weak entity has PARTIAL key ...which seperate a record from set of few tuples not all DATABASE...so the key which is going to be the PRIMARY key for weak entity should have it's own LOCAL attribute in key...

3)yes weak entity borrow attributes from parent entity .....

SO ALL OPTIONS ARE CORRECT...

also 2nd option says that key should contain local attribute from weak entity....it doesnt say that key is completely made up of local attributes... 

Answer 2

Ans b. For point 1. Weak entity cannot have pk formed with its set of attributes but it can have primary key as said in point 3.