UGC NET DBMS Questions Set 1 - ER and Relational Models

Question 1

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1. Given the basic ER and relational models, which of the following is INCORRECT?

1. 1. An attribute of an entity can have more than one value
2. 2. An attribute of an entity can be composite
3. 3. In a row of a relational table, an attribute can have more than one value
4. 4. In a row of a relational table, an attribute can have exactly one value or a NULL value

Answer: (3)
The term 'entity' belongs to ER model and the term 'relational table' belongs to relational model. A and B both are true. ER model supports both multivalued and composite attributes. (C) is false and (D) is true. In Relation model, an entry in relational table can can have exactly one value or a NULL

Question 2

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2. Which of the following relational query languages have the same expressive power?
1. Relational algebra
2. Tuple relational calculus restricted to safe expressions
3. Domain relational calculus restricted to safe expressions

1. 1. II and III only
2. 2. I and II only
3. 3. I and III only
4. 4. I, II and III

Answer: (4)
Relational algebra is a procedural query language where we input - relations and it yields relations as output. It provides method to get the result. It is performed recursively on a relation and the in between results are relations(output). Basic set of operations for the relational model. Relational calculus is a non - procedural query language. It provides the query to get result. Higher level declarative language for specifying relational queries. Tupple Relational Calculus operates on each tupple. Domain Relational Calculus operates on each column or attribute. Safe expression means fixed no. of tupple or column or attribute as a result But all of them has same expressive power. Just different ways to do so

Question 3

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3. What is the min and max number of tables required to convert an ER diagram with 2 entities and 1 relationship between them with partial participation constraints of both entities?

1. 1. Min 1 and max 2
2. 2. Min 1 and max 3
3. 3. Min 2 and max 3
4. 4. Min 2 and max 2

Answer: (3)
Maximum number of tables required is 3 in case of many to many relationships between entities. Minimum number of tables is 1 in case of unary relationship and total participation of atleast one entity. But in case of partial participation of both entities, minimum number of tables required is 2.

Question 4

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4. Consider the join of a relation R with a relation S. If K has m tuples and S has n tuples, then the maximum and minimum sizes of the join respectively are:

1. 1. m+n and 0
2. 2. mn and 0
3. 3. m+n and m-n
4. 4. mn and m+n

Answer: (2)
When there is no foreign key constraint between two tables then the max and min number of tuples in their join is mn and 0 respectively

Question 5

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5. In RDBMS, different classes of relations are created using ___ technique to prevent modification anomalies

1. 1. Functional Dependencies
2. 2. Data integrity
3. 3. Referential integrity
4. 4. Normal Forms

Answer: (4)
Functional dependency is a constraint that describes the relationship between attributes in a relation. Data integrity refers to the accuracy and consistency of data stored in a database, data warehouse, data mart or other construct. Referential integrity is a relational database concept, which states that table relationships must always be consistent. Normalization is a process of organizing the data in database to avoid data redundancy, insertion anomaly, update anomaly & deletion anomaly. 1NF, 2NF, 3NF and BCNF are types of normal forms

Question 6

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6. Which symbol denote derived attributes in ER Model?

1. 1. Double ellipse
2. 2. Dashed ellipse
3. 3. Squared ellipse
4. 4. Ellipse with attribute name underlined

Answer: (2)

Question 7

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7. Goals for the design of the logical scheme include

1. 1. avoiding data inconsistency
2. 2. being able to construct query easily
3. 3. being able to access data efficiently
4. 4. All of the above

Answer: (4)

Question 8

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8. Which one is correct w.r.t. RDBMS ?
1. primary key ⊆ super key ⊆ candidate key
2. primary key ⊆ candidate key ⊆ super key
3. super key ⊆ candidate key ⊆ primary key
4. super key ⊆ primary key ⊆ candidate key

1. 1. 1
2. 2. 2
3. 3. 3
4. 4. 4

Answer: (2)
primary key ⊆ candidate key ⊆ super key in RDBMS For more information Refer:DBMS | Keys in Relational Model (Candidate, Super, Primary, Alternate and Foreign)

Question 9

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9. Let pk(R) denotes primary key of relation R. A many-to-one relationship that exists between two relations R1 and R2 can be expressed as follows :
1. pk(R2) → pk(R1)
2. pk(R1) → pk(R2)
3. pk(R2) → R1 ∩ R2
4. pk(R1) → R1 ∩ R2

1. 1. 1
2. 2. 2
3. 3. 3
4. 4. 4

Answer: (2)

Question 10

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10. Relational database schema normalization is NOT for:

1. 1. reducing the number of joins required to satisfy a query
2. 2. eliminating uncontrolled redundancy of data stored in the database
3. 3. eliminating number of anomalies that could otherwise occur with inserts and deletes
4. 4. ensuring that functional dependencies are enforced

Answer: (1)
Relational database schema normalization is NOT for reducing the number of joins required to satisfy a query
Relational database schema normalization is for eliminating uncontrolled redundancy of data stored in the database
Relational database schema normalization is for eliminating number of anomalies that could otherwise occur with inserts and deletes
Relational database schema normalization is for ensuring that functional dependencies are enforced