Which of the following statements about a relation R in first normal form (1NF) is/are TRUE?
R can have a multi-attribute key
R cannot have a foreign key
R cannot have a composite attribute
R cannot have more than one candidate key
Option A: TRUE, In 1NF multi-attribute key is allowed. Let's have a look at an example of a muti-attributed key in 1NF
Consider a relationship between students and their courses:
StudentID | CourseID | Grade
-------------------------------
101 | COMP101 | A
101 | MATH101 | B
102 | COMP101 | A
103 | MATH101 | C
103 | ENGL101 | B
In the above example, the StudentID and CourseID combined form a multi-attribute key. Any student can be enrolled in multiple courses, and any course can have multiple students.
Together, StudentID and CourseID uniquely identify each record in the relation. Therefore, this relation satisfies that it has a multi-attribute key in 1NF form.
Option B:FALSE, A relation in 1NF can have foreign keys. 1NF doesn't restrict the presence of foreign keys.
Option C:TRUE, Composite attributes are not allowed in 1NF.
What is Composite Attribute in DBMS?
Composite Attributes are attributes that can be further divided or a combination of two or more attributes. For example, the Address attribute can be further divided into Street, City or State. So Address is the composite attribute.
In 1NF, each attribute must be atomic, meaning it cannot be further divided into smaller components.
Option D: False, A relation in 1NF can have more than one candidate key. Each candidate key uniquely identifies tuples in the relation.