Converting ER diagrams to relational schema in DBMS Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Mapping a Weak Entity to a Relational Schema

In an ER diagram, a weak entity depends on a strong entity for its identification. When converting this to a relational schema, how is the weak entity typically represented?

A As a separate table including its own partial key and the primary key of the strong entity as a foreign key

B Merged into the strong entity's table without a separate table

C As a table with only its partial key as the primary key

D Ignored in the relational schema since it cannot exist independently

💡 Hint

Think about how the weak entity depends on the strong entity's key for identification.

A weak entity is represented as a separate table that includes its own partial key and the primary key of the related strong entity. Together, these form the composite primary key of the weak entity's table.

📋 Factual

intermediate

Primary Key Selection for a 1:N Relationship

When converting a one-to-many (1:N) relationship from an ER diagram to a relational schema, how is the relationship typically represented?

A Create a new table with foreign keys from both entities as a composite primary key

B Add the primary key of the 'one' side as a foreign key in the 'many' side table

C Add the primary key of the 'many' side as a foreign key in the 'one' side table

D Ignore the relationship since it is implied by the entities

💡 Hint

Consider which side can hold the foreign key without duplication.

In a 1:N relationship, the primary key of the 'one' side is added as a foreign key in the 'many' side table to represent the relationship.

🔍 Analysis

advanced

Handling Many-to-Many Relationships in Relational Schema

Given an ER diagram with a many-to-many (M:N) relationship between two entities, how should this relationship be converted into a relational schema?

A Create a new table with foreign keys referencing the primary keys of both entities, and use these foreign keys as a composite primary key

B Add the primary key of one entity as a foreign key in the other entity's table

C Merge both entities into a single table to represent the relationship

D Ignore the relationship and rely on application logic to manage it

💡 Hint

Think about how to represent multiple associations between two entities in tables.

A many-to-many relationship is represented by creating a new table that includes foreign keys from both entities. These foreign keys together form the composite primary key of the new table, capturing all associations.

❓ Comparison

advanced

Difference Between Total and Partial Participation in Relational Schema

How does total participation of an entity in a relationship affect the relational schema compared to partial participation?

A Total participation requires merging tables, partial participation requires separate tables

B Total participation means the entity is not included in the schema, partial participation means it is included

C Total participation requires the foreign key to be NOT NULL, while partial participation allows NULL values

D There is no difference in the relational schema between total and partial participation

💡 Hint

Consider how mandatory relationships affect foreign key constraints.

Total participation means every instance of the entity must be related, so the foreign key cannot be NULL. Partial participation means some instances may not be related, so the foreign key can be NULL.

❓ Reasoning

expert

Determining the Number of Tables from an ER Diagram

An ER diagram has 3 strong entities, 1 weak entity dependent on one strong entity, and 2 many-to-many relationships among the strong entities. How many tables will the relational schema have after conversion?

A 7

B 8

C 5

D 6

💡 Hint

Count tables for entities and relationships carefully, including weak entities and M:N relationships.

There are 3 tables for strong entities, 1 for the weak entity, and 2 for the many-to-many relationships, totaling 6 tables.