![]() ![]() The values in an atomic domain are indivisible units. This rule defines that all the attributes in a relation must have atomic domains. First Normal Formįirst Normal Form is defined in the definition of relations (tables) itself. Normalization is a method to remove all these anomalies and bring the database to a consistent state. Insert anomalies − We tried to insert data in a record that does not exist at all. Such instances leave the database in an inconsistent state.ĭeletion anomalies − We tried to delete a record, but parts of it was left undeleted because of unawareness, the data is also saved somewhere else. 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. Update anomalies − If data items are scattered and are not linked to each other properly, then it could lead to strange situations. Managing a database with anomalies is next to impossible. If a database design is not perfect, it may contain anomalies, which are like a bad dream for any database administrator. Non-trivial − If an FD X → Y holds, where Y is not a subset of X, then it is called a non-trivial FD.Ĭompletely non-trivial − If an FD X → Y holds, where x intersect Y = Φ, it is said to be a completely non-trivial FD. Trivial − If a functional dependency (FD) X → Y holds, where Y is a subset of X, then it is called a trivial FD. a → b is called as a functionally that determines b. Transitivity rule − Same as transitive rule in algebra, if a → b holds and b → c holds, then a → c also holds. That is adding attributes in dependencies, does not change the basic dependencies. ![]() Reflexive rule − If alpha is a set of attributes and beta is_subset_of alpha, then alpha holds beta.Īugmentation rule − If a → b holds and y is attribute set, then ay → by also holds. Armstrong's Axioms are a set of rules, that when applied repeatedly, generates a closure of functional dependencies. 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. The left-hand side attributes determine the values of attributes on the right-hand side. , Bn.įunctional dependency is represented by an arrow sign (→) that is, X→Y, where X functionally determines Y. 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. Functional dependency (FD) is a set of constraints between two attributes in a relation. ![]()
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