Database Relationships and Constraints

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Questions and Answers

Which cardinality ratio describes a situation where one entity can be associated with only one entity in another set, while the latter can be associated with multiple entities?

One to one

Many to many

Many to one (correct)

One to many

Which scenario best illustrates a many to many cardinality relationship?

A product can belong to only one category

One manager supervises multiple employees

A student enrolls in multiple courses and each course has multiple students (correct)

An employee is assigned to one department

What is the attribute that uniquely identifies each entity in an entity set called?

Derived Attribute

Key Attribute (correct)

Multivalued Attribute

Composite Attribute

Which type of attribute can consist of multiple values for a single entity?

Multivalued Attribute Signup and view all the answers

What does total participation in the context of participation constraints mean?

All entities must participate in the relationship Signup and view all the answers

Which term describes an entity type that does not have a key attribute and exists only in relation to another entity type?

Weak Entity Type Signup and view all the answers

How is a derived attribute represented in an ER diagram?

Dashed Oval Signup and view all the answers

How is a weak entity typically represented in an entity-relationship diagram?

Double rectangle Signup and view all the answers

Which of the following correctly defines a composite attribute?

An attribute made up of multiple other attributes Signup and view all the answers

What definition best describes a relationship type in the context of entity-relationship modeling?

An association between different entity types Signup and view all the answers

What is the relationship between a weak entity and its identifying entity type called?

Identifying Relationship Signup and view all the answers

Which term best describes a weak entity set?

An entity set that requires additional information to be identified Signup and view all the answers

In a case where an entity claims participation is optional, what type of participation constraint is this?

Partial Participation Signup and view all the answers

Which of the following best represents a condition where each element of one set can appear with any element of another set without restrictions?

Many-to-many relationship Signup and view all the answers

In an ER diagram, which attribute is indicated by a double oval?

Multivalued Attribute Signup and view all the answers

What does the domain of an attribute represent?

The set of potential values that an attribute can take Signup and view all the answers

What is the purpose of aggregation in an ER diagram?

To represent relationships between an entity and a relationship. Signup and view all the answers

Which rule applies to a strong entity set with only simple attributes during ER diagram to table conversion?

It will necessitate one table with attributes matching the entity set's attributes. Signup and view all the answers

How do composite attributes affect the conversion of an ER diagram to a relational model?

Only the simple attributes of composite attributes are considered. Signup and view all the answers

What is one of the key objectives of mapping an ER model?

To provide an overview that aids system understanding. Signup and view all the answers

What does a weak entity set rely on in order to exist?

It depends on the existence of a strong entity set. Signup and view all the answers

Which of the following statements is TRUE regarding strong entity sets?

They can exist independently of other entities. Signup and view all the answers

Which factor is NOT considered when converting a composite attribute in an ER model to a relational schema?

The composite attribute itself. Signup and view all the answers

What aspect of participation constraints is important for effective ER modeling?

They define how many instances of an entity can participate in a relationship. Signup and view all the answers

Study Notes

Cardinality

One-to-One: Each entity in one entity set must be linked to exactly one entity in the other, and vice versa.
One-to-Many: Each entity in one entity set can be linked to multiple entities in the other, but each entity in the other set can only be linked to one entity in the first.
Many-to-One: Each entity in one entity set can be linked to multiple entities in the other, but each entity in the other set can only be linked to one entity in the first.
Many-to-Many: Each entity in one entity set can be linked to multiple entities in the other, and vice versa.

Participation Constraint

Indicates whether an entity must be associated with another entity in a relationship.
Total Participation: All entities in an entity set must participate in the relationship.
Partial Participation: Entities in an entity set may or may not participate in the relationship.

Weak Entity Type

An entity type lacking a key attribute to uniquely identify each entity.
Dependent upon a strong entity type for its existence.
Represented by a double rectangle in an ER diagram.
Has total participation in identifying relationships (double diamond).
Example: Dependent entity type relies on Employee entity type.

Identifying Relationship

Connects a weak entity type to its identifying strong entity type.
Represents the dependency of the weak entity on the strong entity.

Entities, Entity Sets, Attributes

An entity is a real-world object or concept.
An Entity set is a collection of entities of the same type.
Attributes are descriptive properties of an entity or entity set.

Attribute Type

Key Attribute: Uniquely identifies entities in an entity set.
Composite Attribute: Composed of multiple attributes, e.g., Address attribute (Street, City, State, Country).
Multivalued Attribute: Can have multiple values for a single entity (represented by a double oval), e.g., Phone_No.
Derived Attribute: Can be derived from other attributes of the entity type (represented by a dashed oval), e.g., Age (derived from Date of Birth).

Relationship Types

Represents the association between entity types.
Example: "WORKS_FOR" between "Employee" and "Project" entity types.

Aggregation

Used when a relationship needs to relate to another entity not directly involved in the primary relationship.
Represents a relationship within another relationship to capture a more complex structure.
Example: "REQUIRE" relationship between "WORKS_FOR" (which aggregates "Employee" and "Project") and "Machinery" entities.

Reducing ER Diagrams To Tables

Objective: Translate an Entity Relationship (ER) model into a relational schema (tables) for an easier technical understanding.
Rule 01: A strong entity set with only simple attributes maps to a single table.
Rule 02: A strong entity set with composite attributes maps to a single table, including only the simple attributes.

Example:

Entity sets: Customer, Loan
Attributes:
- Customer: customer_id, customer_name, customer_street, customer_city
- Loan: loan_number, amount

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Description

This quiz covers key concepts in database design, including cardinality types such as one-to-one, one-to-many, many-to-one, and many-to-many relationships. It also explores participation constraints and the notion of weak entity types in relational databases. Test your understanding of these critical database principles.