Showing posts with label primary key. Show all posts
Showing posts with label primary key. Show all posts

Friday, 25 January 2013

Explain the difference between a weak and a strong entity set.

Q) Explain the difference between a weak and a strong entity set.


Answer :

A strong entity set has a primary key. All tuples in the set are distinguishable by that key. A weak entity set has no primary key unless attributes of the strong entity set on which it depends are included. Tuples in a weak entity set are partitioned according to their relationship with

Thursday, 3 January 2013

Explain the distinctions among the terms primary key, candidate key, and superkey.

Answer: A superkey is a set of one or more attributes that, taken collectively, allows us to identify uniquely an entity in the entity set. A superkey may contain extraneous attributes. If K is a superkey, then so is any superset of K. A superkey for which no proper subset is also a superkey is called a candidate