Introduction to RDBMS (Relational Database Management System)
In this article, I am going to give you a brief introduction to RDMB (Relational Database Management System). Please read our previous article where we discussed Data Model in DBMS. At the end of this article, you will understand the following pointers in detail.
What is DBMS?
A Database management system is essentially a collection of interrelated data and a set of programs to access this data. This collection of data is called the database. The primary objective of a DBMS is to provide a convenient environment to retrieve and store database information. Database systems support single-user and multi-user environments. While on one hand DBMS permits only one person to access the database at a given time, on the other RDBMS allows many users simultaneous access to the database.
A database system consists of two parts namely, Database Management Systems and Database applications. Database Management System is the program that organizes and maintains the information whereas Database Applications is the program that lets us view, retrieves, and updates information stored in the DBMS.
- The database is a collection of data in one or more files for future reference.
- The database is a collection of interrelated data, i.e. database always stores data along with its relationships.
What is RDBMS?
Relational Database Management System (RDBMS) is an advanced version of a DBMS system. It came into existence during the 1970s. RDBMS system also allows the organization to access data more efficiently than DBMS. It is a software system that is used to store only data which needs to be stored in the form of tables. In this kind of system, data is managed and stored in rows and columns which is known as tuples and attributes RDBMS is a powerful data management system and is widely used across the world.
In order to overcome all the drawbacks of the previous systems, the relational database system got introduced in which data get organized as tables and each record forms a row with many fields or attributes in it. Relationships between tables are also formed in this system.
Example: MySQL, Postgres, SQL Server, Oracle, sap Hana, IBM db2, MariaDB, SQL lite, etc.
Features of RDBMS:
- Provides data to be stored in tables.
- Persists data in the form of rows and columns.
- Provides a primary key to uniquely identify the rows in a table.
- Provides a (view) virtual table creation in which sensitive data can be stored.
- Provides multi-user accessibility that can be controlled by individual users.
- And it features four types of relationships in the database i.e., 1:1, 1:N, N:1, M:N.
- It should be accessed and modified by executing Structured query language (SQL) statements only.
- Should use a set of operators.
- Need not specify the access route to the tables and data.
- There is no need to identify how the data is arranged physically.
How to communicate with RDBMS?
The structured query language is used to communicate with RDBMS.
Advantages of RDBMS:
- The database system in which the relationships among different tables are maintained is called a relational database management system. Both RDBMS and DBMS are used to store information in a physical database.
- RDBMS solutions are required when large amounts of data are to be stored as well as maintained. A relational data model consists of indexes, keys, foreign keys, tables, and their relationships with other tables. Relational DBMS enforces the rules even though foreign keys are support by both RDBMS and DBMS.
- In the 1970s, Edgar Frank Codd introduced the theory of relational databases. Thirteen rules were defined by Codd for this relational theory or model. Relationship among different types of data is the main requirement of the relational model.
- RDBMS can be termed as the next generation of database management systems. DBMS is used as a base model in order to store data in a relational database system. However, complex business applications use RDBMS rather than DBMS.
DBMS vs RDBMS:
- Relationship among tables is maintained in an RDBMS whereas this not the case DBMS as it is used to manage the database.
- DBMS accepts the ‘flat file’ data that means there is no relation among different data whereas RDBMS does not accept this type of design.
- DBMS is used for simpler business applications whereas RDBMS is used for more complex applications.
- Although the foreign key concept is supported by both DBMS and RDBMS, it’s only RDBMS that enforces the rules.
- RDBMS solution is required by large sets of data whereas small sets of data can be managed by DBMS.
E.F. Codd’s Rules:
Rule 1: The information Rule.
“All information in a relational database is represented explicitly at the logical level and in exactly one way – by values in tables.” Everything within the database exists in tables and is accessed via table access routines.
Rule 2: Guaranteed Access Rule.
“Each and every datum (atomic value) in a relational database is guaranteed to be logically accessible by resorting to a combination of the table name, primary key value, and column name.” To access any data-item you specify which column within which table it exists, there is no reading of characters 10 to 20 of a 255-byte string.
Rule 3: Systematic treatment of null values.
“Null values (distinct from the empty character string or a string of blank characters and distinct from zero or any other number) are supported in fully relational DBMS for representing missing information and inapplicable information in a systematic way, independent of data type.” If data does not exist or does not apply then a value of NULL is applied, this is understood by the RDBMS as meaning non-applicable data.
Rule 4: Dynamic online catalog based on the relational model.
“The database description is represented at the logical level, in the same way, as-ordinary data, so that authorized users can apply the same relational language to its interrogation as they apply to the regular data.” The Data Dictionary is held within the RDBMS, thus there is no need for off-line volumes to tell you the structure of the database.
Rule 5: Comprehensive data sub-language Rule.
“A relational system may support several languages and various modes of terminal use (for example, the fill-in-the-blanks mode). However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and that is comprehensive in supporting all the following items
- Data Definition
- View Definition
- Data Manipulation (Interactive and by program).
- Integrity Constraints
Every RDBMS should provide a language to allow the user to query the contents of the RDBMS and also manipulate the contents of the RDBMS.
Rule 6: View updating Rule.
“All views that are theoretically updateable are also updateable by the system.” Not only can the user modify data, but so can the RDBMS when the user is not logged in.
Rule 7: High-level insert, update and delete.
“The capability of handling a base relation or a derived relation as a single operand applies not only to the retrieval of data but also to the insertion, update, and deletion of data.” The user should be able to modify several tables by modifying the view to which they act as base tables.
Rule 8: Physical data independence.
“Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representations or access methods.” The user should not be aware of where or upon which media data-files are stored
Rule 9: Logical data independence.
“Application programs and terminal activities remain logically unimpaired when information-preserving changes of any kind that theoretically permit un-impairment are made to the base tables.” User programs and the user should not be aware of any changes to the structure of the tables (such as the addition of extra columns).
Rule 10: Integrity independence.
“Integrity constraints specific to a particular relational database must be definable in the relational data sub-language and storable in the catalog, not in the application programs.” If a column only accepts certain values, then it is the RDBMS that enforces these constraints and not the user program, this means that an invalid value can never be entered into this column, whilst if the constraints were enforced via programs there is always a chance that a buggy program might allow incorrect values into the system.
Rule 11: Distribution independence.
“A relational DBMS has distribution independence.” The RDBMS may spread across more than one system and across several networks, however to the end-user the tables should appear no different to those that are local.
Rule 12: Non-subversion Rule.
“If a relational system has a low-level (single-record-at-a-time) language, that low level cannot be used to subvert or bypass the integrity Rules and constraints expressed in the higher-level relational language (multiple-records-at-a-time).”
Here, in this article, I try to give you an overview of RDBMS (Relational Database Management System). I hope you enjoy this article.