Relational Model
Introduction
- The Relational model stores data in the form of tables. This concept is introduced by Dr. E.F. Codd, a researcher at IBM. The relational model is the first choice of commercial data processing applications for storing the data.
- Relational model is most famous because of its simplest structure as compared to other database models like network or hierarchic models.
- The relational model is now considered the primary model for databa,ses./
- The relational data model is the simple model having all the properties and capabilities required to process data.
- Most modern Database Management Systems (DBMS) are relational.
- The relational model consists of three major components :
l. The set of relations and set of domains that define 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).
- In the relational database model, the data is stored in different tables. These tables are interlinked with each other with the help of common fields (columns) in between them.
History of the relational model
- Edgar Codd introduced the relational model as a general model of data.
- Codd proposed the relational model for IBM,
But Codd has no idea that his influential work would become the basis of relational databases.
- The relational model is later maintained and developed by Chris Date and Hugh Darwen.
- Date and Darwen shows that the relational model contains some desired object-oriented features in the Third Manifesto.
Definition of Relational Model
- A relational database is a collective combination of data structures, storage and retrieval operations, and integrity constraints.
- In such a database the data and relations between them are organized into tables.
- Table is the collection of records.
3.1.2 Characteristics of Relational Database
The characteristics of Relational database systems are as follows :
This model is called as Relational Model by Dr. Codd because the data is stored in the tables which are having relationships between them.
The whole data of the system is represented as a systematic arrangement of data into ·rows and columns, called a relation or table.
A table is also formed in a two-dimensional structure.
At any given row/column position means in every cell in the relation there is one and only one value which is known as a Scalar Value.
Advantages of Relational Model
t. Ease of use: The system which is managed in the form.. of tables consisting of rows and columns is much easier to understand.
2. Flexibility: The information from multiple tables can be retrieved easily at a time by joining the tables. Also, changes can be done easily 1:iy Using different operators.
3. Security: Different users can have different levels of access to data based on their roles. In the college database, students will h e-access to their own data only, while there,.teachers will have access to data of all the students to whom they are teaching. Class teacher Will be able to see the reports of all the students m that class, but not other classes. The principal will have access to the entire data.
4. Data Independence : [n Relational system we can completely separate the data structure of the database and programs or applications which are used to access the data. This is called data independence. If any changes are made in the structure of the database then there is no need to make changes in the programs. For example, you can modify the size or data type of data items (fields of a database table) without making any change in the application.
5. Data Manipulation Language: In the relational database approach it is easy to respond query using a language like SQL based on relational algebra and relational calculus. For data organized in other structures the query language either becomes complex or extremely limited in its capabilities.
Basic Concepts of Relational Model
tables:
The relational model refers table as its basic unit.
- In the relational model-related data is collectively carried in the structured format ir. the database system.
- It is a combination of rows and columns, where records are represented by rows and attributes are represented by columns. In the relational data model, relations ·are sav. ed in the format of Tables. The relations among entities are stored in this format.
Tuple
- Tuple is a single row of the table. It contains a whole record of a particular data item. For example, in the Student table the entire information about a specific student like his roll number, name, marks, etc. is included in the tuple.
A tuple is an ordered set of attribute values.
Attribute
- It is a column of a table. For example in a table Student, there may be different attributes like roll_number, stud_name, marks, etc.
- Every attribute is attached with a specific data type which decides which type of values can be inserted in those attributes.
- Attributes are also known as fields.
Domain
Every attribute has some pre-defined value scope, known as the attribute domain.
- This attribute domain decides which types of Val es are permitted in the attribute.
The type of value contains where the string or numerical or date type. The domain also decides some integrity constraints for values to be inserted
into the database. For example, an emp_name attribute can have only a string type of value while the salary attribute can have only numeric values with a specified range.
Domain restricts the data to be inserted with specific constraints, hence it is called a domain constraint.
Properties of relational database model
Data is presented in the relational database model
like it is the collection of relations.
- Each relation is considered as a table.
- Columns are attributes that belong to the entity modeled by the table.
- Each row (Tuple) represents a single entity.
Every table has a set of attributes collectively called a "key" which uniquely identifies each row.
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