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What is a functional dependency (FD) for relation R?
A functional dependency for relation R is a formula of the form Aïƒ B where A and B are sets of attributes of R. A is called the LHS (left hand side) and B is called the RHS (right hand side), and we say the LHS functionally determines the RHS, or the RHS is functionally dependent on the LHS.
What is the meaning of a functional dependency?
The meaning of the functional dependency is that for every value of A, there is a unique value of B. The FD holds for R if, for any instance of R, whenever two tuples agree in value for all attributes of A, they also agree in value for all attributes of B.
Give an example of a functional dependency for the relation Student(studentID, name, DateOfBirth, phoneNumber) assuming each student has only one name.
The following functional dependency holds: {studentID} ïƒ {name, DateOfBirth}
In the given example, assuming a student may have multiple phone numbers, does the FD {studentID} ïƒ {phoneNumber} hold for the table?
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What is the convention often used when representing sets in functional dependencies?
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What is the significance of the LHS and RHS in a functional dependency formula?
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Explain the meaning of a functional dependency for relation R.
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In the context of the relation Student(studentID, name, DateOfBirth, phoneNumber), what functional dependency holds assuming each student has only one name?
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In the given example, assuming a student may have multiple phone numbers, does the FD {studentID} ïƒ {phoneNumber} hold for the table?
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Why is it common to omit the curly braces { } for the set when representing functional dependencies?
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Study Notes
Functional Dependencies
- A functional dependency (FD) is a formula of the form A ïƒ B, where A and B are sets of attributes of a relation R.
- In a functional dependency, A is called the LHS (left-hand side) and B is called the RHS (right-hand side).
- The LHS functionally determines the RHS, meaning that for every value of A, there is a unique value of B.
- A functional dependency holds for a relation R if, for any instance of R, whenever two tuples agree in value for all attributes of A, they also agree in value for all attributes of B.
Examples of Functional Dependencies
- For the relation Student(studentID, name, DateOfBirth, phoneNumber), the functional dependency studentID ïƒ name, DateOfBirth holds, assuming each student has only one name and date of birth.
- However, the functional dependency studentID ïƒ phoneNumber does not hold, assuming a student may have multiple phone numbers.
Notation Convention
- By convention, curly braces { } for the set are often omitted, and the functional dependency is written as A ïƒ B.
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Description
Test your understanding of functional dependencies in relation R with this quiz. Explore formulas, left hand side (LHS), right hand side (RHS), and the concept of functional dependency in a relational database.
