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
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
(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.