SQL Server Relational Properties

RDBMS

Relational Data Base Management Systems (RDBMS) are database management systems that maintain data records and indexes in tables. Relationships may be created and maintained across and among the data and tables. In a relational database, relationships between data items are expressed by means of tables. Inter dependencies among these tables are expressed by data values.

 

Properties of the Relational Tables

Relational tables have the following properties:

• Values are atomic.
• Each row is unique.
• The sequence of columns is insignificant.
• The sequence of rows is insignificant.
• Each column must have a unique name.

 

Normalization

Database normalization is a data design and organization process applied to data structures based on rules that help building relational databases. In relational database design, the process of organizing data to minimize redundancy is called normalization. Normalization usually involves dividing a database into two or more tables and defining relationships between the tables.

 

De-normalization

De-normalization is the process of attempting to optimize the performance of a database by adding redundant data. A relational DBMS would allow for a fully normalized database at the logical level, while providing physical storage of data that is tuned for high performance. De-normalization is a technique to move from higher to lower normal forms of database modelling in order to speed up database access.

 

Normalization Forms

 

1NF: Eliminate Repeating Groups

Make a separate table for each set of related attributes, and give each table a primary key. Each field contains at most one value from its attribute domain.

 

2NF: Eliminate Redundant Data

If an attribute depends on only part of a multi-valued key, then remove it to a separate table.

 

3NF: Eliminate Columns

If attributes do not contribute to a description of the key, then remove them to a separate table. All attributes must be directly dependent on the primary key.

 

BCNF: Boyce-Codd Normal Form

If there are non-trivial dependencies between candidate key attributes, then separate them out into distinct tables.

 

4NF: Isolate Independent Multiple Relationships

No table may contain two or more 1:n or n:m relationships that are not directly related.

 

5NF: Isolate Semantically Related Multiple Relationships

There may be practical constrains on information that justify separating logically related many-to-many relationships.

 

ONF: Optimal Normal Form

A model limited to only simple (elemental) facts, as expressed in Object Role Model notation.

 

DKNF: Domain-Key Normal Form

A model free from all modification anomalies is said to be in DKNF.

Remember, these normalization guidelines are cumulative. For a database to be in 3NF, it must first fulfil all the criteria of a 2NF and 1NF database.