The process of organizing data into tables in such a way that the results of using the database are always unambiguous and as intended. Normalization is typically a refinement process after the initial exercise of identifying the data objects that should be in the database, identifying their relationships, and defining the tables required and the columns within each table. First normal form (1NF) is the "basic" level of normalization: Data and information are contained in two-dimensional tables with rows and columns. Each column corresponds to a sub-object or an attribute of the object represented by the entire table. Each row represents a unique instance of that sub-object or attribute and must be different in some way from any other row (that is, no duplicate rows are possible). All entries in any column must be of the same kind. For example, in the column labeled "Date," only dates are permitted. In Second normal form (2NF), the tables are in first normal form and, in addition, each column in a table that is not a determiner of the contents of another column must itself be a function of the other columns in the table. At the second normal form, modifications are still possible because a change to one row in a table may affect data that refers to this information from another table. In Third normal form (3NF), the tables are in second normal form and, in addition, there is no transitive functional dependency. For example, if A is functionally dependent on B, and B is functionally dependent on C, then C is transitively dependent on A via B. In Domain/key normal form (DKNF), a key uniquely identifies each row in a table. A domain is the set of permissible values for an attribute. By enforcing key and domain restrictions, the database is assured of being freed from modification anomalies. DKNF is the normalization level that most designers aim to achieve.
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