CSC 375: Relational Database Design

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Questions and Answers

What is required to represent an M:N relationship type?

A single foreign key in one of the participating relations

A composite primary key in both relations

A primary key in each participating relation

A separate relationship relation (correct)

How is the primary key of a relation created for a multivalued attribute?

It is a combination of the multivalued attribute and the primary key of the original entity. (correct)

It is created by concatenating all attributes in the relation.

It is a foreign key referencing the primary key of the original entity only.

It includes only the simple components of the composite multivalued attribute.

What must be included in the relation that represents an n-ary relationship type?

A single foreign key for the primary relationship

Just the attributes without foreign keys

Foreign keys of all participating entity types and any simple attributes of the relationship (correct)

Only the primary key of the relationship

When determining the primary key of an n-ary relation, what must be considered if any entity type has a cardinality constraint of 1?

The foreign key for that entity type should not be included. Signup and view all the answers

What is true about mapping multivalued attributes in a relation?

Simple components of the composite multivalued attribute also need to be included as attributes. Signup and view all the answers

What is the primary requirement when using the foreign key approach for mapping a binary 1:1 relationship?

One of the relations should include the primary key of the other as a foreign key. Signup and view all the answers

When should the merged relationship approach be preferred in mapping a binary 1:1 relationship?

When the two entity types have total participation in the relationship. Signup and view all the answers

In mapping a binary 1:N relationship using the foreign key approach, where should the foreign key be placed?

In the relation representing the N-side of the relationship. Signup and view all the answers

What is usually included in the relation representing a binary M:N relationship type?

The primary keys of both entity types, forming the primary key of the new relation. Signup and view all the answers

Which approach is generally recommended for mapping binary 1:1 relationship types?

Utilizing the foreign key approach. Signup and view all the answers

When mapping a binary 1:N relationship, what must be true of the entity instances on the N-side?

Each instance can relate to only one entity instance on the 1-side. Signup and view all the answers

What is a potential drawback of having foreign keys in both relations for a binary 1:1 relationship?

It creates redundancy, leading to consistency maintenance issues. Signup and view all the answers

What must be included as attributes in the relation representing a binary M:N relationship type?

Simple attributes of the M:N relationship type. Signup and view all the answers

What is the primary purpose of mapping regular entity types in a relational database schema?

To establish primary keys and ensure uniqueness for relations. Signup and view all the answers

What additional step is necessary when mapping weak entity types?

Include the primary key of the owner entity as a foreign key. Signup and view all the answers

In the context of relational database design, what does mapping a binary 1:N relationship typically involve?

Including a foreign key in the relation representing the 'N' side. Signup and view all the answers

What is the significance of composite attributes in mapping entity types?

Only simple components of a composite attribute should be included as attributes. Signup and view all the answers

When dealing with multiple keys identified for a regular entity type during design, what should be maintained in the relational schema?

Descriptions of attributes that form each additional unique key. Signup and view all the answers

Which of the following correctly describes the primary key of a relation representing a weak entity type?

It is formed from the primary keys of the owner entity and the weak entity's partial key. Signup and view all the answers

What is the correct approach to mapping multivalued attributes in a relational schema?

Create a separate relation for the multivalued attributes. Signup and view all the answers

How should the mapping of N-ary relationship types be approached in relational database design?

An independent relation must be created to represent the N-ary relationship. Signup and view all the answers

Study Notes

Objectives of Relational Database Design

Learn to design a relational database schema based on conceptual schema design.
Understand the logical database design step, also referred to as data model mapping.
Follow procedures to create a relational schema from an entity-relationship (ER) schema.

Steps of ER-to-Relational Mapping

Mapping involves various steps to convert conceptual ER diagrams into relational schemas:
- Mapping of Regular Entity Types
- Mapping of Weak Entity Types
- Mapping of Binary 1:1 Relationship Types
- Mapping of Binary 1:N Relationship Types
- Mapping of Binary M:N Relationship Types
- Mapping of Multivalued Attributes
- Mapping of N-ary Relationship Types

Mapping of Regular Entity Types

Create relations for each regular (strong) entity type including all simple attributes.
Include only simple component attributes of composite attributes.
Select one of the key attributes as the primary key for the relation.
If multiple keys exist, keep information about them for additional unique keys and indexing.

Mapping of Weak Entity Types

Create a relation for each weak entity type including all simple attributes.
Add primary key attributes from the owner entity as foreign keys in the new relation.
The primary key for the relation combines the owner's primary key and any partial key of the weak entity.
Map weak entities in order of their ownership hierarchy.

Mapping of Binary 1:1 Relationship Types

Identify relations for the entity types involved in the 1:1 relationship.
Utilize the foreign key approach by including the primary key of one relation as a foreign key in the other.
Alternatively, use a merged relationship approach if both participations are total.

Mapping of Binary 1:N Relationship Types

For regular binary 1:N relationships, identify the relation for the N-side.
Include the primary key of the 1-side entity relation as a foreign key in the N-side relation.
Add any simple attributes of the relationship as attributes of the N-side relation.

Mapping of Binary M:N Relationship Types

Create a new relation to represent the M:N relationship type.
Include primary keys of the participating entity relations as foreign key attributes in the new relation.
Combine these foreign keys to form the primary key for the new relation.
Add any simple attributes of the M:N relationship as attributes in the relation.

Mapping of Multivalued Attributes

Create a new relation for each multivalued attribute.
Include the multivalued attribute and the primary key as a foreign key.
The primary key for the new relation is the combination of the multivalued attribute and the foreign key.
Include simple components of composite multivalued attributes as needed.

Mapping of N-ary Relationship Types

For n-ary relationships (where n > 2), create a new relation to represent the relationship.
Include primary keys of all participating entity relations as foreign keys in this new relation.
Add any simple attributes of the n-ary relationship type to the new relation.
Typically, the primary key is a combination of all foreign keys; if an entity has constraints of 1, its corresponding foreign key may be excluded from the primary key.

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Description

This quiz covers the principles of designing a relational database schema, focusing on the logical database design step known as data model mapping. It explores the procedures for creating a relational schema from an entity-relationship (ER) schema diagram. Understand the key concepts necessary for effective database management systems.