Relational Model

Relational Model

Relational model stores data in the form of tables. The relational model consists of three major components:

1. The set of relations and set of domains that defines the way data can be represented (data structure).

2. Integrity rules that define the procedure to protect the data (data integrity).

3. The operations that can be performed on data (data manipulation).

A relational model database is defined as a database that allows you to group its data items into one or more independent tables that can be related to one another by using fields common to each related table.

Characteristics of Relational Database

The whole data is conceptually represented as an orderly arrangement of data into rows and columns, called a relation or table.

All values are scalar. That is, at any given row/column position in the relation there is one and only one value.

All operations are performed on an entire relation and result is an entire relation, a concept known as closure.

Cardinality of a relation

The number of tuples in a relation determines its cardinality. In this case, the relation has a cardinality of 4.

Degree of a relation

Each column in the tuple is called an attribute. The number of attributes in a relation determines its degree. The relation in has a degree of 3.

Domains

A domain definition specifies the kind of data represented by the attribute. More particularly, a domain is the set of all possible values that an attribute may validly contain. Domains are often confused with data types, but this is inaccurate.

Data type is a physical concept while domain is a logical one. "Number" is a data type and "Age" is a domain. To give another example "StreetName" and "Surname" might both be represented as text fields, but they are obviously different kinds of text fields; they belong to different domains.

Body of a Relation

The body of the relation consists of an unordered set of zero or more tuples. There are some important concepts here. First the relation is unordered. Record numbers do not apply to relations. Second a relation with no tuples still qualifies as a relation. Third, a relation is a set. The items in a set are, by definition, uniquely identifiable. Therefore, for a table to qualify as a relation each record must be uniquely identifiable and the table must contain no duplicate records.

Keys