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 Normalization Definition Used to identify relations based on keys and functional dependencies. Normalization Characteristics -minimal number of attributes necessary to support the data requirements of the enterprise; -attributes with a close logical relationship are found in the same relation; -minimal redundancy with each attribute represented only once with the important exception of attributes that form all or part of foreign keys. Normalization Benefits -easier for the user to access and maintain the data; -take up minimal storage space on the computer. *minimize data redundancy eliminating update anomolies Update Anomolies Relations with potential data redundancy problems that could lead to insertion, deletion, and modification anomalies. Loss-less Join and Dependency Properties -Lossless-join property enables us to find any instance of the original relation from corresponding instances in the smaller relations. -Dependency preservation property enables us to enforce a constraint on the original relation by enforcing some constraint on each of the smaller relations. Functional Dependencies -Describes relationship between attributes. -if A and B are attributes of relation R, B is functionally dependent on A (denoted A -> B), if each value of A in R is associated with exactly one value of B in R. Determinant of a functional dependency -refers to the attribute or group of attributes on the left-hand side of the arrow. Full Functional Dependency -Determinants should have the minimal number of attributes necessary to maintain the functional dependency with the attribute(s) on the right hand-side. -Full functional dependency indicates that if A and B are attributes of a relation, B is fully functionally dependent on A, if B is functionally dependent on A, but not on any proper subset of A. Normalization Functional Dependencies -There is a one-to-one relationship between the attribute(s) on the left-hand side (determinant) and those on the right-hand side of a functional dependency. -Holds for all time. -The determinant has the minimal number of attributes necessary to maintain the dependency with the attribute(s) on the right hand-side. Transitive Dependency _Describes a condition where A, B, and C are attributes of a relation such that if A → B and B → C, then C is transitively dependent on A via B (provided that A is not functionally dependent on B or C). -Potential source for update anomolies Process of Normalization -Formal technique for analyzing a relation based on its primary key and the functional dependencies between the attributes of that relation. -Each step corresponds to a specific normal form, which has known properties. Purpose in identifying functional dependencies for a relation -To specify the set of integrity constraints that must hold on a relation. -An important integrity constraint to consider first is the identification of candidate keys, one of which is selected to be the primary key for the relation. As normalization proceeds -Relations become progressively more restricted (stronger) in format and also less vulnerable to update anomalies. Unnormalized Form (UNF) A table that contains one or more repeating groups. First Normal Form (1NF) A relation in which the intersection of each row and column contains one and only one value. UNF to 1NF -Nominate an attribute or group of attributes to act as the key for the unnormalized table. -Identify the repeating group(s) in the unnormalized table which repeats for the key attribute(s). -Remove the repeating group Remove the repeating group; UNF to 1NF -Entering appropriate data into the empty columns of rows containing the repeating data (‘flattening’ the table). Or by -Placing the repeating data along with a copy of the original key attribute(s) into a separate relation. Second Normal Form (2NF) -Based on the concept of full functional dependency. -Full functional dependency indicates that if A and B are attributes of a relation, B is fully dependent on A if B is functionally dependent on A but not on any proper subset of A. -A relation that is in 1NF and every non-primary-key attribute is fully functionally dependent on the primary key. 1NF to 2NF -Identify the primary key for the 1NF relation. -Identify the functional dependencies in the relation. -If partial dependencies exist on the primary key remove them by placing then in a new relation along with a copy of their determinant. Third Normal Form (3NF) -Based on the concept of transitive dependency. -Transitive Dependency is a condition where A, B and C are attributes of a relation such that if A -> B and B -> C, then C is transitively dependent on A through B. (Provided that A is not functionally dependent on B or C). Third Normal Form (3NF) A relation that is in 1NF and 2NF and in which no non-primary-key attribute is transitively dependent on the primary key. 2NF to 3NF -Identify the primary key in the 2NF relation. -Identify functional dependencies in the relation. -If transitive dependencies exist on the primary key remove them by placing them in a new relation along with a copy of their dominant. Second normal form (2NF) A relation that is in first normal form and every non-primary-key attribute is fully functionally dependent on any candidate key. Third normal form (3NF) A relation that is in first and second normal form and in which no non-primary-key attribute is transitively dependent on any candidate key.