Question :
What do you mean by closure of a set of functional dependencies.
Subject
Database Management System
Standard
Computer Science Engineering
Views
566
Asked By
Dashboard
Prisha
Answer / Solution
Answer / Solution
In database theory, the closure of a set of functional dependencies is the set of all attributes that can be determined from the attributes in the set using the inference rules known as Armstrong's Rules.
The closure of a set of functional dependencies can be calculated using the following steps:
- Add the attributes that are present on the left-hand side of the functional dependencies in the set.
- Add the attributes that are present on the right-hand side of the functional dependencies in the set.
- Use the attributes that are present in the closure to check if there are any other attributes that can be derived from the other functional dependencies in the set. Repeat this step until no new attributes can be derived.
The closure of a set of functional dependencies is a useful tool for database designers. It can be used to identify all of the attributes that are functionally dependent on a given set of attributes. This information can be used to improve the design of the database by ensuring that all of the data is stored in a consistent and efficient manner.
For example, consider the following set of functional dependencies:
Code snippet
A → B
B → C
The closure of this set of functional dependencies is {A, B, C}. This means that any value for A will determine a value for B, which will in turn determine a value for C. This information can be used to design a database table that stores the data for these three attributes in a consistent and efficient manner.
The closure of a set of functional dependencies can also be used to identify redundant functional dependencies. A functional dependency is redundant if it can be inferred from other functional dependencies in the set. For example, the functional dependency B → C is redundant in the above set of functional dependencies, because it can be inferred from the functional dependency A → B.
Identifying and removing redundant functional dependencies can improve the performance of database queries. This is because redundant functional dependencies can lead to unnecessary data being scanned during a query.
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