Functional Dependency Functional dependency (FD) is a set of constraints between two attributes in a relation. Functional dependency says that if two tuples have same values for attributes A1, A2,..., An, then those two tuples must have to have same values for attributes B1, B2, ..., Bn. Functional dependency is represented by an arrow sign (→) that is, X→Y, where X functionally determines Y. The left-hand side attributes determine the values of attributes on the right-hand side. Armstrong's Axioms If F is a set of functional dependencies then the closure of F, denoted as F+, is the set of all functional dependencies logically implied by F. Armstrong's Axioms are a set of rules, that when applied repeatedly, generates a closure of functional dependencies. Reflexive rule − If alpha is a set of attributes and beta is_subset_of alpha, then alpha holds beta. Augmentation rule − If a → b holds and y is attribute set, then ay → by also holds. That is adding attribut...
If a database design is not perfect, it may contain anomalies, which are like a nightmare for any database administrator. Managing a database with anomalies is next to impossible.There are different types of anomalies which can occur in referencing and referenced relation which can be discussed as: Insertion anomaly We tried to insert data in a record that does not exist at all. Deletion anomalies We tried to delete a record, but parts of it was left undeleted because of unawareness, the data is also saved somewhere else. Update anomalies If data items are scattered and are not linked to each other properly, then it could lead to strange situations. For example, when we try to update one data item having its copies scattered over several places, a few instances get updated properly while a few others are left with old values. Such instances leave the database in an inconsistent state. Normalization is a method to remove all these anomalies and bring the da...