Relational Model in DBMS

Relational Model in DBMS

The relational database model derived from the mathematical concept of relation and set theory. It was proposed as a technique to data modeling by Dr Edgar F. Codd of IBM Analysis in 1970 in his document entitled “A Relational Technique of Information for Huge Shared Data Banks.” This document marked the start of the field of a relational database.

The relational model is based on concept of a relationship that is physically defined as a table. In this model, tables are used to hold data about the object to be set in the database. A relation is defined as a two-dimensional table in which rows of the table correspond to single records, and the columns correspond to attributes. Each row is known as a tuple, and each column is known as an
attribute.

Domain

A domain is a collection of atomic values. Atomic defines that each value in the domain is hidden to the relational model. A domain is generally specified by name, data type, format, and constrained range of values. For example, as shown in figure attribute EMP-NO, it is a domain whose data type is an integer with a value ranging between 1, 00,000 and 2, 00, 00. Attributes are the properties that specify a relationship. For example, EMP-NO, NAME.

Attributes

Attributes are the properties that prescribe a relation. For example, EMP-NO, EMP-NAME.

Relation Schema

The relation schema refers to the mechanism of a table.

Example: EMPLOYEE (EMP-NO, EMP-NAME, DATE-OF-BIRTH, SEX, TEL-NO, and SALARY) is a relation schema for EMPLOYEE. If a schema has greater than one relation, it is known as Relational Schema.

Tuple

Each sequence in the relation is called a tuple. The relation includes 6 tuples, one of which is shown as:

Relation Instance

The set of records of a relation at a specific instance of time is known as relation instance. The table shows the relation example of EMPLOYEE at a particular time. It can modify every time there is an insertion, deletion, or updation in the database.

Degree

The number of columns in the table is known as the degree of the relation. EMPLOYEE relation has degree 6.

Cardinality

The number of rows in a table is called the cardinality of the relation. EMPLOYEE relation has cardinality 6.

NULL Values

The value which is anonymous or not available is known as a NULL Value. It is described by blank space.

Example

Operations of the Relational Model

1. Insertion

   Deletion is also secure. For example, delete a tuple from EMPLOYEE relation in a figure whose EMP-NO is 112233.

2. Deletion

   Deletion is also secure. For example, delete a tuple from EMPLOYEE relation in a figure whose EMP-NO is 112233.

3. Updation

   Updation is also easy. For example, change the salary of an employee whose EMP-NO is 123243 from 38,000 to 42,000.

   Hence, in the relational model, insertion, deletion, and updation operation are quite comfortable.

Advantages of the Relational Model

The advantages of the relational model approach are as follows:

Ease of Use

The revision of any record as tables including rows and columns is quite natural and therefore, even first time client as follows finds it attractive.

Security

Security control and authorization can also be implemented more by merely changing sensitive attributes in a given table into a separate association with its authorization controls. If the authorization requirement authorizes, a specific attribute could be joined back with others to allow full data retrieval.

Data Independence

Data independence is accomplished more simply with organization architecture used in a relational database than in the more complex tree or network structure.

Flexibility

Different tables from which data has to be connected and extracted can be simply manipulated by operators such as a project and joint to give data in the structure in which it is desired.

Precision

The procedure of relational algebra and relational evaluation in the manipulation of the relations among the tables secure that there is no bug, which may differently arise in establishing the linkage in a complex network type database.

Data Manipulation Language

The possibility of responding to Adhoc query using a language based on relational algebra and relational calculus is accessible in the relational database technique. For data organized in other mechanisms, the query language either develops into complicated or extremely limited in its capabilities.

Disadvantages of the Relational Model

The disadvantages of relational model approach are as follows:

Cost

One disadvantage of relational databases is the cost of setting up and keeping up the database framework. To set up a relational database, we generally want to buy specific software. If we are not a developer, we can use several products to set up relational databases. It does not take time to enter in all the information and set up in the program.

Abundance of Information

Advances in the complexity of data cause another limitation to relational databases. Relational databases are made for organizing information by common characteristics. Complex images, numbers, designs, and multimedia items defy simple categorization leading the technique for a new type of database known as object-relational database management frameworks. These frameworks are designed to manage more complex functions and can be versatile.

Structured Limits

Some relational databases have restrictions on area lengths. When we design the database, we have to specify the amount of data we can fit into a field. Some names or search queries are shorter than the actual, and this can lead to information loss.

Properties of Relational Tables

The properties of relational tables which are as follows:

Values are Atomic

This feature includes columns in a relational table that are not copying class and arrays. Hence, composite and multi-valued attributes are not allowed.

Every row is different

This feature gives that no two rows in a relational table are interchangeable.

The series of columns is unimportant

This features provides that the series of columns in the relational table has no implication. A column can be reconstructed in any order and numerous series.

The series of a row is unimportant

This feature ensures that the sequencing of rows in the relational table has no implication.

Each column has a unique name

This property states that the name of each column should be unique.

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