Relational Database Model in DBMS
The relational model was introduced in 1970 by E. F. Codd. The relational model foundation is a mathematical concept known as a relation.
The relational model is implemented through a very sophisticated relational database management system (RDBMS).
The RDBMS performs the same basic functions provided by the hierarchical and network DBMS systems, in addition to a host of other functions that make the relational data model easier to understand and implement.
Arguably the most important advantage of the RDBMS is its ability to hide the complexities of the relational model from the user. The RDBMS manages all of the physical details, while the user sees the relational database as a collection of tables in which data are stored. The user can manipulate and query the data in a way that seems intuitive and logical.
A relational table stores a collection of related entities. In this respect, the relational database table resembles a file. But there is one crucial difference between a table and a file:
A table yields complete data and structural independence because it is a purely logical structure. How the data are physically stored in the database is of no concern to the user or the designer.
Another reason for the relational data model’s rise to dominance is its powerful and flexible query language.
For most relational database software, the query language is Structured Query Language (SQL), which allows the user to specify what must be done without specifying how it must be done.
The RDBMS uses SQL to translate user queries into instructions for retrieving the requested data. SQL makes it possible to retrieve data with far less effort than any other database or file environment.
From an end-user perspective, any SQL-based relational database application involves three parts: a user interface, a set of tables stored in the database, and the SQL “engine.” Each of these parts is explained below.
The end-user interface:
Basically, the interface allows the end user to interact with the data (by auto-generating SQL code).
Each interface is a product of the software vendor’s idea of meaningful interaction with the data.
You can also design your own customized interface with the help of application generators that are now standard fare in the database software arena.
A collection of tables stored in the database:
In a relational database, all data are perceived to be stored in tables.
The tables simply “present” the data to the end user in a way that is easy to understand.
Each table is independent. Rows in different tables are related by common values in common attributes.
SQL engine:
Largely hidden from the end user, the SQL engine executes all queries, or data requests. Keep in mind that the SQL engine is part of the DBMS software.
The end user uses SQL to create table structures and to perform data access and table maintenance.
The SQL engine processes all user requests—largely behind the scenes and without the end user’s knowledge.
Advantages of Relational Model in DBMS
The different advantages of Relational model are as follows:
1. Structural independence
2. Improved conceptual simplicity
3. Easier database design, implementation, management, and user
4. Ad hoc query capability (SQL)
5. Powerful database management system
Disadvantages of Relational Model in DBMS
The different disadvantages of Relational model are as follows:
1. Substantial hardware and system software overhead
2. Possibility of poor design and implementation
3. Potential “islands of information” problems
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