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What is a functional dependency (FD) for relation R?
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?
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.
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?
In the given example, assuming a student may have multiple phone numbers, does the FD {studentID} ïƒ {phoneNumber} hold for the table?
What is the convention often used when representing sets in functional dependencies?
What is the convention often used when representing sets in functional dependencies?
What is the significance of the LHS and RHS in a functional dependency formula?
What is the significance of the LHS and RHS in a functional dependency formula?
Explain the meaning of a functional dependency for relation R.
Explain the meaning of a functional dependency for relation R.
In the context of the relation Student(studentID, name, DateOfBirth, phoneNumber), what functional dependency holds assuming each student has only one name?
In the context of the relation Student(studentID, name, DateOfBirth, phoneNumber), what functional dependency holds assuming each student has only one name?
In the given example, assuming a student may have multiple phone numbers, does the FD {studentID} ïƒ {phoneNumber} hold for the table?
In the given example, assuming a student may have multiple phone numbers, does the FD {studentID} ïƒ {phoneNumber} hold for the table?
Why is it common to omit the curly braces { } for the set when representing functional dependencies?
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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