Databases

Terms:

Cardinality: with respect to tables, the number of rows in the table. With respect to indexed columns, the number of distinct values of that column in a table.
Normalization is the process of restructuring a data model by reducing its relations to their simplest forms. It is a key step in the task of building a logical relational database design. Normalization reduces redundancy from your data and can improve the performance of update and delete statements, since you only have to do it in one place. By normalizing your data, you try to ensure that all columns in the table depend on the primary key. The disadvantage of a fully normalized data structure is in data retrieval operations, specifically when a query is accessing a large number of related pieces of data from different tables via join operations. For more information about Normalization, author C.J. Date is one of the better resources.
Denormalization is the intentional duplication of columns in multiple tables whose consequence is increased data redundancy. Denormalization is sometimes necessary to minimize performance problems and is a key step in designing a physical relational database design.

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