The main goal of a database management system is to allow it's customers to perform a numerous procedures about the the database, for example insert, delete and retrieve data in abstract terms without knowing about the physical representations of data. To provide the different facilities to various kinds of customers, a DBMS usually a number of specific programming languages called Database(or DBMS) Languages. The actual DBMS mainly offers two database languages, specifically, Data deﬁnition Language(DDL) and Data Manipulation Language to implement the databases. Data deﬁnition language (DDL) can be used for deﬁning the actual database schema. The actual DBMS includes DDL compiler that identiﬁes as well as stores the schema description in the DBMS catalog. Data manipulation language (DML) can be used to manipulate the database.
In DBMS where no strict separation between the levels of the database is maintained, the data deﬁnition language can be used in order to deﬁne the actual conceptual and as well as inner schemas for the database. However, in DBMS, where a clear separation is maintained between the conceptual and as well as inner levels, the DDL is used to specify the conceptual schema only. Such DBMS, a separate language, specifically, storage deﬁnition language (SDL) can be used in order to deﬁne the internal schema. Some of the DBMSs which provide accurate three-schema architecture use a third language, specifically, view deﬁnition language(VDL)to deﬁne the exterior schema.
The actual DDL statements will also used to specify the integrity rules (constraints) in order to maintain the integrity of the database. The different integrity constraints are domain constraints, referential integrity, assertions and authorization.
Once the database schemas tend to be deﬁned and also the initial data is loaded into the database, several operations for example retrieval, insertion, deletion and modiﬁcation can be applied to the database. The DBMS provides data manipulation language (DML) that allows customers to retrieve and manipulate the data. The statement which is used to retrieve the information is called a query. The part of the DML used to retrieve the information is called a query language. However, query language and DML are used synonymously though technically incorrect. The DML are of two types, namely, non-procedural DML and procedural DML.
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