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# Relational Data Manipulation Languages:

## Definition and explanation:

In relational database management systems, different database languages are used to manipulate data. These languages may be procedural, non-procedural, graphical language, 4GL etc. Some RDBMSs use natural language, sometimes called a fifth generation language.

## Categories of Relational Data Manipulation Languages:

Different relational data manipulation languages are proposed to manipulate the relational database. The most important categories of relational data manipulation languages are:

(i) Relational Algebra in DBMS

(ii) Relational Calculus

(iii) Transform-Oriented Languages

(iv) Query-By-Example and Query-By-Form

### (i) Relational Algebra in DBMS:

Relational Algebra is a theoretical procedural language. The relational algebra is not a user-friendly language. Relational algebra has relational operators that are used to perform various operations on relations. The relational algebra operator uses relations as operands, performs the operation on the relations and returns another relation as output result.

Relational algebra is not directly used in commercial database processing, because no commercial DBMS product provides relational algebra facilities. The relational algebra helps to learn. SQL because the syntaxes of SQL statements are similar to the syntax of relational algebra expressions.

### (ii) Relational Calculus:

Relational calculus is a non-procedural relational data manipulation language. It enables user to specify what data to be retrieved, but not how to retrieve the data. The relational calculus is a formal query language. It is not related to the mathematics calculus. The relational calculus is not easy to learn and to use. It is not used in commercial database processing.

Domain relational calculus is another type of relational calculus. In this type of relational calculus, the variables are used that take values from domains instead of tuples of relations.

### (iii) Transform-Oriented Languages:

Transform-oriented languages are non-procedural data manipulation languages that transform input data expressed as relations into results expressed as a single relation. These languages are very easy to learn and to use for manipulating data. SQL and SQUARE are examples of Transform-Oriented languages. The most popular and commonly used transform-oriented language in commercial DBMS is SQL.

### (iv) Query-By-Example and Query-By-Form:

Query-By-Example (QBE) and Query-By-Form (QBF) are graphical relational database languages. These languages provide the graphical interface to manipulate data of database.

Query-By-Example (QBE) is one of the first graphical query language. It is developed by IBM and is available in IBM commercial product. This language is also implemented in the Paradox DBMS. It differs from SQL in that the user does not have to specify a structured query explicitly; rather the query is formulated by filling in templates of relations that appear on the monitor screen. The user does not have to remember the names of relations and their attributes because they are displayed as part of these templates. QBE is related to the domain relational calculus.

## Relevant Articles:

 Logical Database Design Relational Data Model Relation in database (DBMS) Data Integrity Rules Relational Data Manipulation Languages Relational Algebra Operators in DBMS Codd's 12 Rules For the Relational Model

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