Data Models: CODD’s Rules

Dr. Edgar F. CODD proposed a set of rules that are necessary for a system to qualify as a Relational Database  Management  System.  The CODD’s  rules  are  as follows:

1. Operations on Relational Model

The basic operations that can be performed on relational data model are insertion, deletion, updation and  retrieval. All these  operations are discussed  briefly:

1. Insertion : The Insert Operation  is used  to Insert  a new  record into the

The data values into the tables will not be inserted when the following conditions occurs which  are  as  follows:

• If we enter a duplicate value for the attribute which is chosen as a primary key.
• If we try to insert a NULL value in Primary key attribute.
• If we try to insert data value in foreign key attribute which does not exist in the corresponding Primary key attribute.
• If an attribute is given a value that does not appear in the corresponding domain.

2. Deletion : The delete operation is used to delete a record from the table.
3. Updation : The updation operation is used to update the data values of a record in the table, in other words, it is used to change the data values of one or more attributes in a tuple(s) of some Updating an attribute that is neither a Primary key nor a foreign key causes no problems, only there is need to check that the new value  is  of  correct  data  type  and  domain.

But if we update a data value of the Primary key attribute then there is need to check.

• Modified value does not have a corresponding foreign key value.
• New value should not already exist  in the table.

4. Retrieval : The retrieval operation is used to search and fetch a record from the This operation is very simple and symmetric as compared to previous models.

Advantages of Relational Model

The major  advantages of  Relational Model  are  as follows:

• Simplicity : The Relational database model is very easy and simple to design and implement at the logical The different tables in the database can be designed using appropriate attributes and data values very easily. All the relations are designed in a tabular manner, which helps the user to concentrate on the logical view of the database rather than  complex  internal  details  of how  data  is  stored.

• Flexible : The Relational databse provide flexibility that allows changes to database structure to be  easily accommodated.
• Data Independence : Because data resides in tables, the structure of database can be changed without having to change any applications that were based on the If you are using non relational database you probably have to modify the application that will access this information by including pointers to the new data. But with relational database the information is immediately accessible because it is automatically related to  other  data  by virtue  of  its  position  in the  table.
• Structural Independence : Relational database is only concerned with data and not with the structures, which improves performance. Hence processing time and storage space is comparatively large in relational database but the user is not required to know the details of the structure The structural flexibility of a relational database allows combinations of data to be retrieved that were never anticipated at the time the database was initially designed.
• Query Capability : It makes possible a high level query language e., SQL (Structure Query Language) which avoids complex database navigation. In this model the queries are based on logical relationships and processing those queries does not require predefined access paths  among  the data  i.e.,  pointers.
• Matured Technology : Relational model is useful for representing most of the real world objects and relationship between Relationship implementation is very easy through the use  of a  key.
• Ability to easily take advantages of new hardware technology which make things easy for the users.

Disadvantages of Relational Model

The major disadvantages of relational data  moderate are as follows:

• The relational database use a simple mapping of logical tables to physical structures. Indexing and hashing techniques are used for access to table data and for certain constraint This  severally  limits  the  performance.
• The most significant limitation of relational model is its limited ability to deal with binary large objects such as images, spreadsheets,  e-mail messages, documents etc.
• Since this model has the ability to easily take advantage of new hardware technology to run smoothly, so large hardware overheads are This make it a costly affair.
• Mapping objects to relational database can be  a difficult skill  to learn.
• Data Integrity is difficult to ensure with relational databases because no single application has control over the data so it is very difficult to ensure that all applications are operating under business The individual database will also create problems like data  duplication,  data  inconsistency  and  so on.

Commercially Available Relational Database Systems

There are number of Database systems based on relational model. Some of them are as follows:

1. Oracle
2. Sy-base
3. MAGNUM
4. IBM’s Query by example
5. NOMAD systems of NCSS.

Source: Gupta Satinder Bal, Mittal Aditya (2017), Introduction to Basic Database Management System, 2nd Edition-University Science Press (2017)