Conceptual data models and entity relationship modelling：練習問題

When producing an entity relationship diagram, what notation is typically used to represent an entity that uniquely identifies a record in a table?

Consider a data model for a car rental system. A Customer can make multiple Bookings, but each Booking belongs to only one Customer. What is the degree of this relationship?

Consider the following entity descriptions for a retail system:
Order(OrderID, OrderDate, CustomerID)
Product(ProductID, Description, Price)

If an Order can contain many Products and a Product can be part of many Orders, what is the most appropriate way to represent the 'OrderLine' entity in an ERD?

In conceptual data modelling, which of the following best describes the relationship between a 'Student' and a 'Course' in a typical university database where a student can enrol in multiple courses and a course can have many students?

A company database needs to store information about Employees and Departments. Each Employee works in exactly one Department, but a Department can have many Employees. How should this be represented in an Entity Relationship Diagram (ERD)?

In entity-relationship modelling, what does a many-to-many (M:N) relationship usually require when being mapped to a relational database schema?

Consider a school database. A Student table and a Class table exist. If a student can attend multiple classes and a class has many students, describe the attributes of the resulting link table Enrolment in terms of keys.

In an Entity Relationship Diagram (ERD), how is a many-to-one relationship represented between a Department entity and an Employee entity, assuming one employee works in one department?

A database designer is creating a system for a music festival. They start by identifying that an Artist performs at a Stage, and a Stage can host many Artists. Each Artist belongs to exactly one RecordLabel, but a RecordLabel may have many Artists signed to it.

a. State the degree of the relationship between Artist and RecordLabel. (1 point)

b. Draw an Entity Relationship Diagram (ERD) to represent the relationships between Artist, Stage, and RecordLabel, assuming an Artist only performs on one Stage. (2 points)

A developer is designing a database for a university. A Department can employ many Lecturers, but each Lecturer belongs to exactly one Department. Additionally, a Lecturer can teach many Modules, and a Module can be taught by many Lecturers.

(a) Produce the entity descriptions for the entities Department, Lecturer, and Module, identifying primary and foreign keys. (3 points)
(b) Explain why a 'link table' is required for the relationship between Lecturer and Module and provide its entity description. (3 points)