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 procedures to protect the data (data integrity).
3. The operation that can be operate on the 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.
Basic terminology used in relational model
Attributes Emp_code Name Year
12 Saurav 1984
Tuples 13 Chirag 1985
14 Jagdeep 1983
Tuples of a Relation: Each row in data is actually a tuple.
Cardinality of a Relation: The number of tuples in a relation determines its cardinality.
Degree of relation: Each column in the tuple is called attribute. The umber of attributes in tuple determines its degree.
Domain: a domain. Specifies the type of data represented by the attribute or a dom
ain is all kind of values that an attribute can validly contain.
Domains are often confused by data types; data type is physical concept while domain is logical. Number is data type and age is domain.
Keys of a Relation: it is a set of one or more columns whose combined values are unique. Some different types of keys are:
Primary key: primary key is an attribute or set of attributes of relation which posses the properties of uniqueness.
Foreign Key: foreign Key is the attribute of a table, which refers to the primary key of some other table. Foreign key permits only those values, which appear in the primary key of the table to which it refers.
Advantages of Relational Model:
Conceptual Simplicity: We have seen that both the hierarchical and network models are conceptually simple, but relational model is simpler than both of those two.
Structural Independence: In the Relational model, changes in the structure do not affect the data access.
Design Implementation: the relational model achieves both data independence and structural independence.
Ad hoc query capability: the presence of very powerful, flexible and easy to use capability is one of the main reason for the immense popularity of the relational database model.
Disadvantages of Relational Model:
Hardware overheads: relational database systems hide the implementation complexities and the physical data storage details from the user. For doing this, the relational database system need more powerful hardware computers and data storage devices.
Ease of design can lead to bad design: the relational database is easy to design and use. The user needs not to know the complexities of the data storage. This ease of design and use can lead to the development and implementation of the very poorly designed database management system.