Entity-Relationship model in DBMS Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Entities and Attributes

In an Entity-Relationship (ER) model, which statement correctly describes the difference between an entity and an attribute?

A An entity represents a real-world object or concept, while an attribute describes properties or characteristics of that entity.

B An attribute represents a real-world object, while an entity describes properties of that attribute.

C Entities and attributes are the same and can be used interchangeably in ER diagrams.

D An attribute is a relationship between two entities.

💡 Hint

Think about what you want to represent as a thing versus what describes that thing.

Entities are objects or concepts like 'Student' or 'Car'. Attributes are details about entities, like 'Name' or 'Color'.

📋 Factual

intermediate

Cardinality in Relationships

What does the cardinality 'one-to-many' mean in an ER model?

A Many entity instances in the first set can be associated with only one instance in the second set, and vice versa.

B One entity instance in the first set can be associated with many instances in the second set, but each instance in the second set is associated with only one instance in the first set.

C Each entity instance in both sets can be associated with many instances in the other set.

D Each entity instance in both sets can be associated with only one instance in the other set.

💡 Hint

Consider the direction of 'one' and 'many' in the relationship.

One-to-many means one entity on the left relates to many on the right, but each on the right relates to only one on the left.

🔍 Analysis

advanced

Identifying Weak Entities

Given an ER diagram where an entity 'OrderItem' depends on 'Order' for its identification, which characteristic best identifies 'OrderItem' as a weak entity?

A 'OrderItem' is connected to 'Order' by a many-to-many relationship.

B 'OrderItem' has a unique primary key independent of 'Order'.

C 'OrderItem' has a partial key and cannot be uniquely identified without 'Order'.

D 'OrderItem' has no attributes.

💡 Hint

Think about what makes an entity weak in terms of identification.

A weak entity depends on another entity for its key; it has a partial key that needs the owner's key to be unique.

❓ Comparison

advanced

Difference Between Generalization and Specialization

Which option correctly distinguishes between generalization and specialization in the ER model?

A Generalization combines several entities into a higher-level entity, while specialization divides an entity into lower-level entities based on differences.

B Generalization divides an entity into sub-entities, while specialization merges entities into one.

C Both generalization and specialization mean the same and can be used interchangeably.

D Generalization is used only for attributes, specialization only for relationships.

💡 Hint

Think about whether you are grouping or splitting entities.

Generalization groups entities into a broader category; specialization breaks an entity into more specific types.

❓ Reasoning

expert

Determining the Number of Relationships

Consider an ER model with entities 'Student', 'Course', and 'Instructor'. Each student can enroll in many courses, and each course can have many students. Each course is taught by exactly one instructor, but an instructor can teach many courses. How many total relationships are there in this model?

A Four relationships: Student-Course, Course-Instructor, Student-Instructor, and Instructor-Student.

B Three relationships: Student-Course, Course-Instructor, and Student-Instructor.

C One relationship: Student-Course-Instructor combined.

D Two relationships: one between Student and Course, and one between Course and Instructor.

💡 Hint

Count only direct relationships between entities described.

There are two direct relationships: students enroll in courses, and courses are taught by instructors. No direct relationship between students and instructors is described.