RDBMS

Introduction to the Relational Model

Question 1
Marks : +2 | -2
Pass Ratio : 100%
What is the method of specifying a primary key in a schema description?
By writing it in bold letters
By underlining it using a dashed line
By writing it in capital letters
By underlining it using a bold line
Explanation:
We can specify a primary key in schema description by underlining the respective attribute with a bold line.
Question 2
Marks : +2 | -2
Pass Ratio : 100%
Choose the option that correctly explains in words, the function of the following relational algebra expression
Selects all tuples from the Cartesian product of book and borrow
Selects all the tuples from the natural join of book and borrow wherever the year is lesser than 2009
Selects all the tuples from the natural join of book and student wherever the year is greater than or equal to 2009
Selects all tuples from the Cartesian product of book and borrow wherever the year is greater than or equal to 2009
Explanation:
The condition under the select statement represents the condition that must be satisfied by the tuples and the symbol ⋈ represents natural join between the two relations on either side of the operator.
Question 3
Marks : +2 | -2
Pass Ratio : 100%
State true or false: If a relation consists of a foreign key, then it is called a referenced relation of the foreign key dependency.
True
False
Explanation:
If a relation has a foreign key, then it is called a referencing relation of the foreign key dependency.
Question 4
Marks : +2 | -2
Pass Ratio : 100%
What does the “x” operator do in relational algebra?
Output specified attributes from all rows of the input relation. Remove duplicate tuples from the output
Output pairs of rows from the two input relations that have the same value on all attributes that have the same name
Output all pairs of rows from the two input relations (regardless of whether or not they have the same values on common attributes)
Returns the rows of the input relation that satisfy the predicate
Explanation:
The “x” operator outputs all pairs of rows from the two input relations (regardless of whether or not they have the same values on common attributes). This operation is called as the Cartesian product operation and is similar to the Cartesian product of sets.
Question 5
Marks : +2 | -2
Pass Ratio : 100%
What is a foreign key?
A foreign key is a primary key of a relation which is an attribute in another relation
A foreign key is a superkey of a relation which is an attribute in more than one other relations
A foreign key is an attribute of a relation that is a primary key of another relation
A foreign key is the primary key of a relation that does not occur anywhere else in the schema
Explanation:
A foreign key is an attribute of a relation that is initially a primary key of another relation. A foreign key usage preserves referential integrity.
Question 6
Marks : +2 | -2
Pass Ratio : 100%
An attribute is a __________ in a relation.
Row
Column
Value
Tuple
Explanation:
An attribute is a column in a relation. A tuple is a row in a relation.
Question 7
Marks : +2 | -2
Pass Ratio : 100%
Statement 1: A tuple is a row in a relation
Both the statements are true
Statement 1 is correct but Statement 2 is false
Statement 1 is false but Statement 2 is correct
Both the statements are false
Explanation:
A tuple is a row is a relation. There can exist multiple foreign keys in the same relation because there can exist multiple attributes in the relation that are primary keys in two or more other relations.
Question 8
Marks : +2 | -2
Pass Ratio : 100%
What action does ⋈ operator perform in relational algebra
Output specified attributes from all rows of the input relation and remove duplicate tuples from the output
Outputs pairs of rows from the two input relations that have the same value on all attributes that have the same name
Output all pairs of rows from the two input relations (regardless of whether or not they have the same values on common attributes)
Return rows of the input relation that satisfy the predicate
Explanation:
⋈ Outputs specified attributes from all rows of the input relation. Remove duplicate tuples from the output. The operation is called the join operation.
Question 9
Marks : +2 | -2
Pass Ratio : 100%
What is an Instance of a Database?
The logical design of the database system
The entire set of attributes of the Database put together in a single relation
The state of the database system at any given point of time
The initial values inserted into the Database immediately after its creation
Explanation:
The state of the database system at any given point of time is called as an Instance of the database.
Question 10
Marks : +2 | -2
Pass Ratio : 100%
Choose the correct statement regarding superkeys
A superkey is an attribute or a group of multiple attributes that can uniquely identify a tuple
A superkey is a tuple or a set of multiple tuples that can uniquely identify an attribute
Every superkey is a candidate key
A superkey is an attribute or a set of attributes that distinguish the relation from other relations
Explanation:
A superkey is an attribute or a set of multiple attributes that can uniquely identify a tuple. It is used to differentiate between tuples.