This topic Normalisation is of Relational Database.
Before Discussing them I am just briefing the following topics
Relation?
Entity ?
Keys?
These will be discussed in next slide.
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Relation
Entity
Attribute
Attribute Values
Record
Tuple
Domain also
Primary Key and
Secondary Key
However, some of the Keys to be in discussion
Super Key
A super key is a primary key for a relation is a set of attributes that uniquely identifies a tuple.
Candidate Key
A candidate key is also a super key such that no proper subset is a super key.
Foreign Key
A foreign key is an attribute of a relation that is the primary key of another relations. So We can call the relation in which the attribute is the primary key is home relation.
Our Concern
In this lecture we discuss some of the theory that has been developed to attempt to choose GOOD relations or relational models also know as relational schema – that is to measure formally why one set of grouping of attributes into relations is better than another.
There are two levels at which we can discuss the goodness of relations.
The first is the logical level, which refers to how the users interpret the relations and meaning of other attributes.However, having good relations at this level helps the users to understand clearly the meaning of the data tuples in the relations, and hence to formulate their queries correctly.
And, the second is the manipulation (or storage) level, which refers to how the tuple in a base relation are stored and updated.
So we can say that this level applies only to base relations – which will physically stored as files- whereas at the logical level we are interested in both base relations and views.
Objectives of NormaliSation
The basic objective of logical modeling is to develop a good description of the data, its relationships, and its constraints. So for the relational model, this means that we must identify a suitable set or relations. However, the task of choosing the relations is a difficult one, because there are many options for the designer to consider. That’s why the techniques presented here are based on a large body of research in to the logical design process called Normalisation.
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