Which of the following correctly describes a foreign key in the entity-relationship (ER) diagram?

Question

BlackTom AI · Accepted Answer

A foreign key is an attribute on the “many” side of a one-to-many relationship that stores values matching the primary key of the related “one” table, enforcing referential integrity. In the diagram, CustomerID in tblCustomers has a key symbol (primary key). The relationship between tblCustomers and tblSales shows “1” at tblCustomers and “∞” at tblSales, meaning one customer can have many sales. Therefore the foreign key must appear in the tblSales record to link a sale back to its customer.

Step-by-step reasoning:
1. Identify primary keys: CustomerID in tblCustomers and MovieID in tblMovies show key icons, so they are primary keys.
2. Identify relationship cardinality: The connector between tblCustomers and tblSales is 1-to-many (1 at customers, ∞ at sales). Similarly for tblMovies to tblSales.
3. Apply the foreign-key rule: In a one-to-many relationship, the foreign key is placed on the “many” side (tblSales) and stores the primary key value from the “one” side (tblCustomers).
4. Inspect tblSales attributes: tblSales lists CustomerID and MovieID (without key icons), indicating they are attributes referencing keys in other tables — these are foreign keys.

Why the correct answer is correct:
- CustomerID in tblSales is the attribute that references tblCustomers.CustomerID (the primary key), so it functions as a foreign key linking a sale to a customer.

Why other options are incorrect:
- a. SalesID in tblSales is the primary key of tblSales, not a foreign key.
- c. CustomerID in tblCustomers is the primary key of the customers table, not a foreign key.
- d. MovieID in tblMovies is the primary key of the movies table, not a foreign key (the foreign key would be MovieID in tblSales).

Conclusion: CustomerID in tblSales correctly describes a foreign key, so the correct choice is b.

Which of the following correctly describes a foreign key in the entity-relationship (ER) diagram?单项选择题

类似问题

Following are the definitions of 2 tables in a DBMS: EMPLOYEE(EmpID,FirstName,LastName,PositionID,Salary) POSITION(PositionID,PositionName,DeptID,EmplID) What is the foreign key in the Table EMPLOYEE?

Question 15

A table in a database can contain more than one foreign key.

In a relational database management system, what is a foreign key?

The attribute ClientID in the Orders table would be considered

If participation of EMPLOYEE in DEPARTMENT is optional, what is the typical implication for the DEPARTMENT_ID foreign key in EMPLOYEE?

All tables in relational databases must have a foreign key.

In relational databases, it is possible to have more than one foreign key in a single table.

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