The Database Management System (DBMS)
DBMS A software system that enables users to define, create, maintain, and control
access to the database.
The DBMS is the software that interacts with the users’ application programs and the
database. Typically, a DBMS provides the following facilities:
n It allows users to define the database, usually through a Data Definition Language
(DDL). The DDL allows users to specify the data types and structures and the constraints
on the data to be stored in the database.
It allows users to insert, update, delete, and retrieve data from the database, usually
through a Data Manipulation Language (DML). Having a central repository for all
data and data descriptions allows the DML to provide a general inquiry facility to this
data, called a query language. The provision of a query language alleviates the problems
with file-based systems where the user has to work with a fixed set of queries or
there is a proliferation of programs, giving major software management problems. The
most common query language is the Structured Query Language (SQL, pronounced
‘S-Q-L’, or sometimes ‘See-Quel’), which is now both the formal and de facto standard
language for relational DBMSs. To emphasize the importance of SQL, we devote
Chapters 5 and 6, most of 28, and Appendix E to a comprehensive study of this language.
n It provides controlled access to the database. For example, it may provide:
– a security system, which prevents unauthorized users accessing the database;
– an integrity system, which maintains the consistency of stored data;
– a concurrency control system, which allows shared access of the database;
a recovery control system, which restores the database to a previous consistent state
following a hardware or software failure;
– a user-accessible catalog, which contains descriptions of the data in the database.
DBMS A software system that enables users to define, create, maintain, and control
access to the database.
The DBMS is the software that interacts with the users’ application programs and the
database. Typically, a DBMS provides the following facilities:
n It allows users to define the database, usually through a Data Definition Language
(DDL). The DDL allows users to specify the data types and structures and the constraints
on the data to be stored in the database.
It allows users to insert, update, delete, and retrieve data from the database, usually
through a Data Manipulation Language (DML). Having a central repository for all
data and data descriptions allows the DML to provide a general inquiry facility to this
data, called a query language. The provision of a query language alleviates the problems
with file-based systems where the user has to work with a fixed set of queries or
there is a proliferation of programs, giving major software management problems. The
most common query language is the Structured Query Language (SQL, pronounced
‘S-Q-L’, or sometimes ‘See-Quel’), which is now both the formal and de facto standard
language for relational DBMSs. To emphasize the importance of SQL, we devote
Chapters 5 and 6, most of 28, and Appendix E to a comprehensive study of this language.
n It provides controlled access to the database. For example, it may provide:
– a security system, which prevents unauthorized users accessing the database;
– an integrity system, which maintains the consistency of stored data;
– a concurrency control system, which allows shared access of the database;
a recovery control system, which restores the database to a previous consistent state
following a hardware or software failure;
– a user-accessible catalog, which contains descriptions of the data in the database.
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