RDBMS is acronym for Relation Database Management System. Dr. E. F. Codd first introduced the Relational Database Model in 1970. The Relational model allows data to be represented in a simple row- column. Each data field is considered as a column and each record is considered as a row. Relational Database is more or less similar to Database Management System. In relational model there is relation between their data elements. Data is stored in tables. Tables have columns, rows and names. Tables can be related to each other if each has a column with a common type of information. The most famous RDBMS packages are Oracle, Sybase and Informix. Simple example of Relational model is as follows :
Student Details Table:
Roll_no Sname S_Address
--------------------------------------------
1 Rahul Satelite
2 Sachin Ambawadi
3 Saurav Naranpura
Student Marksheet Table:
Rollno Sub1 Sub2 Sub3
---------------------------------------------
1 78 89 94
2 54 65 77
3 23 78 46
Here, both tables are based on students details. Common field in both tables is Rollno. So we can say both tables are related with each other through Rollno column.
Degree of Relationship
=> One to One (1:1)
=> One to Many or Many to One (1:M / M: 1)
=> Many to Many (M: M)
The Degree of Relationship indicates the link between two entities for a specified occurrence of each.
One to One Relationship : (1:1)
One student has only one Rollno
For one occurrence of the first entity, there can be, at the most one related occurrence of the second entity, and vice-versa.
One to Many or Many to One Relationship: (1:M/M: 1):
As per the Institutions Norm, One student can enroll in one course at a time however, in one course, there can be more than one student.
For one occurrence of the first entity there can exist many related occurrences of the second entity and for every occurrence of the second entity there exists only one associated occurrence of the first.
Many to Many Relationship: (M:M):
The major disadvantage of the relational model is that a clear-cut interface cannot be determined. Reusability of a structure is not possible. The Relational Database now accepted model on which major database system are built. Oracle has introduced added functionality to this by incorporated object-oriented capabilities. Now it is known is as Object Relational Database Management System (ORDBMS). Object- oriented concept is added in Oracle8.
Some basic rules have to be followed for a DBMS to be relational. They are known as Codd’s rules, designed in such a way that when the database is ready for use it encapsulates the relational theory to its full potential. These twelve rules are as follows.
E. F. Codd Rules:
=> The Information Rule
All information must be store in table as data values.
=> The Rule of Guaranteed Access
Every item in a table must be logically addressable with the help of a table name.
=> The Systematic Treatment of Null Values
The RDBMS must be taken care of null values to represent missing or inapplicable information.
=> The Database Description Rule
A description of database is maintained using the same logical structures with which data was defined by the RDBMS.
=> Comprehensive Data Sub Language
According to the rule the system must support data definition, view definition, data manipulation, integrity constraints, authorization and transaction management operations.
=> The View Updating Rule
All views that are theoretically updateable are also updateable by the system.
=> The Insert and Update Rule
This rule indicates that all the data manipulation commands must be operational on sets of rows having a relation rather than on a single row.
=> The Physical Independence Rule
Application programs must remain unimpaired when any changes are made in storage representation or access methods.
=> The Logical Data Independence Rule
The changes that are made should not affect the user’s ability to work with the data. The change can be splitting table into many more tables.
=> The Integrity Independence Rule
The integrity constraints should store in the system catalog or in the database.
=> The Distribution Rule
The system must be access or manipulate the data that is distributed in other systems.
=> The Non-subversion Rule
If a RDBMS supports a lower level language then it should not bypass any integrity constraints defined in the higher level.
Student Details Table:
Roll_no Sname S_Address
--------------------------------------------
1 Rahul Satelite
2 Sachin Ambawadi
3 Saurav Naranpura
Student Marksheet Table:
Rollno Sub1 Sub2 Sub3
---------------------------------------------
1 78 89 94
2 54 65 77
3 23 78 46
Here, both tables are based on students details. Common field in both tables is Rollno. So we can say both tables are related with each other through Rollno column.
Degree of Relationship
=> One to One (1:1)
=> One to Many or Many to One (1:M / M: 1)
=> Many to Many (M: M)
The Degree of Relationship indicates the link between two entities for a specified occurrence of each.
One to One Relationship : (1:1)
For one occurrence of the first entity, there can be, at the most one related occurrence of the second entity, and vice-versa.
One to Many or Many to One Relationship: (1:M/M: 1):
For one occurrence of the first entity there can exist many related occurrences of the second entity and for every occurrence of the second entity there exists only one associated occurrence of the first.
Many to Many Relationship: (M:M):
Some basic rules have to be followed for a DBMS to be relational. They are known as Codd’s rules, designed in such a way that when the database is ready for use it encapsulates the relational theory to its full potential. These twelve rules are as follows.
E. F. Codd Rules:
=> The Information Rule
All information must be store in table as data values.
=> The Rule of Guaranteed Access
Every item in a table must be logically addressable with the help of a table name.
=> The Systematic Treatment of Null Values
The RDBMS must be taken care of null values to represent missing or inapplicable information.
=> The Database Description Rule
A description of database is maintained using the same logical structures with which data was defined by the RDBMS.
=> Comprehensive Data Sub Language
According to the rule the system must support data definition, view definition, data manipulation, integrity constraints, authorization and transaction management operations.
=> The View Updating Rule
All views that are theoretically updateable are also updateable by the system.
=> The Insert and Update Rule
This rule indicates that all the data manipulation commands must be operational on sets of rows having a relation rather than on a single row.
=> The Physical Independence Rule
Application programs must remain unimpaired when any changes are made in storage representation or access methods.
=> The Logical Data Independence Rule
The changes that are made should not affect the user’s ability to work with the data. The change can be splitting table into many more tables.
=> The Integrity Independence Rule
The integrity constraints should store in the system catalog or in the database.
=> The Distribution Rule
The system must be access or manipulate the data that is distributed in other systems.
=> The Non-subversion Rule
If a RDBMS supports a lower level language then it should not bypass any integrity constraints defined in the higher level.
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