Single Valued Normalisation
Codd in the year 1972 formed three normal forms (1NF, 2NF, and 3NF). These were based on functional dependencies between the attributes of a relation. Later Codd and Boyce proposed another normal form known as the Boyce-Codd normal form (BCNF). The fourth and fifth normal forms are based on multivalue and join dependencies and were proposed soon. In this part we will do normal forms till BCNF only. Fourth and fifth normal forms are afar the scope of this course. For all practical purposes, BCNF or the3NF are quite adequate since they remove the anomalies talk about for most common situations. It should be obviously understood that there is no obligation to normalise relations to the maximum possible level. Performance should be engaged into account and sometimes an organisation may take a decision not to normalise, say, beyond third normal form. But, it should be noted that such designs should be careful sufficient to take care of anomalies that would result as of the decision above.
Intuitively, the second and third normal forms are planned to result in relations such that each relation have information about only one thing (either an relationship or a entity). A sound E-R model of the database would make sure that all relations either give facts about an entity or about a relationship resulting in the relations that are get being in 2NF or 3NF.
Normalisation results in decomposition of the original relation. It should be noted that decomposition of relation has to be always rely on principles, such as functional dependence, that ensure that the original relation may be reconstructed from the decomposed relations if and when needed. Careless decomposition of a relation can result in loss of information. We will talk about this in detail in the later section. Let us now describe these normal forms in more detail.