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What is the concept of canonical cover?
A canonical cover is a simplified and reduced version of the given set of functional dependencies. Since it is a reduced version, it is also called as Irreducible set.
What is the use of canonical cover?
Whenever a user updates the database, the system must check whether any of the functional dependencies are getting violated in this process. If there is a violation of dependencies in the new database state, the system must roll back.
Is a minimal cover unique?
Minimal covers are not unique: for 3NF design we use a particular kind of minimal cover, called a canonical cover. Canonical covers are computed as follows: Decompose fds into non-trivial fds that have only one attribute at the right side.
What’s the difference between canonical cover and minimal cover?
The goal in calculating the Canonical is to provide a minimum, in matters or redundancy. canonical cover is to produce the minimal FD from the closure set F+ .The main factor of bring down for canonical closure is to ensure that there are no redundant dependencies in our database.
When do you roll back a canonical cover?
In case of a violation of functional dependencies in the new database state, the rollback of the system must take place. A canonical cover or irreducible a set of functional dependencies FD is a simplified set of FD that has a similar closure as the original set FD.
How to find canonical cover of functional dependencies?
Consider the following set F of functional dependencies: Steps to find canonical cover: A BC. Now, the revised set F becomes: There is an extraneous attribute in AB C because even after removing AB C from the set F, we get the same closures.
How to find the canonical cover in javatpoint?
Example: Given a relational Schema R ( A, B, C, D) and set of Function Dependency FD = { B → A, AD → BC, C → ABD }. Find the canonical cover? Solution: Given FD = { B → A, AD → BC, C → ABD }, now decompose the FD using decomposition rule ( Armstrong Axiom ). Now set of FD = { B → A, AD → B, AD → C, C → A, C → B, C → D }