Question

When is the conceptual schema of a database changed?-

if we update data in the database

-if we alter the logical structure of the database

-if we retrieve data from the database

-if we alter the storage structure of the database

Which of the following has the same meaning as the outer union?

Group of answer choices

-the left outer (natural) join

-the right outer (natural) join

-the full outer (natural) join

-the inner (natural) join

Assume {A, B} is the primary key of relation schema R(A, B, C). Which of the following statements is NOT true:

Group of answer choices

{ A, B} must be unique

{A, B} must be a candidate key of R

A or B may have a NULL value

{A, B} must be a superkey

Which of the following examples is NOT an integrity constraint on a database:

Group of answer choices

A student name must be a string with a length ≤ 30

Database user ‘James’ cannot update data in the database

If two students have the same birthday, their ages must be the same

Every student must have a home address

Which of the following statements is true?

Group of answer choices

A foreign key may reference an attribute in its own relation

A relation can have only one foreign key

A foreign key cannot have a NULL value

A foreign key must reference the primary key of the referenced relation

The data dictionary in a database system is used to keep:

Group of answer choices

database schema

database instance

temporary data

final query result

Entities for a weak entity type can be uniquely identified by:

Group of answer choices

all attributes together of the weak entity type

the partial key of the weak entity type

a key of the owner entity type

the combination of (B) and (C)

Answer 1

Ans 6:

The data dictionary is used to keep

A. Database schema

Reason :

It's used to store metadata , i.e. data about the database and hence data schema is correct.

Ans 7:

A weak entity can be identified by

A. all attributes together of the weak entity type

Reason : a weak doesn't have primary key so the only optionto identify it is through it's attributes.