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DBMS: Components and Three Level Architecture
In this tutorial, we will learn about the different components of DBMS, and Three Level Architecture of DBMS.
By Prerana Jain Last updated : May 26, 2023
Database management system is partitioned into modules for different functions. Some functions may be provided by the operating system. Broadly the functional component of the database system are:
DBMS Components
1) Query Processor
It is one of the functional components of DBMS. The database manager understands that the query processor translates statements into low-level instructions in a query language. It may also attempt to find an equivalent but more efficient form.
It contains the following components:
- DML Compiler: The DML compiler converts DDL(data definition language) statements in the form of tables which stored metadata in a data dictionary. It also performs query optimization.
- DDL Interpreter: It is a device which interprets the DDL statements and some records into the data dictionary.
- Query Evaluation Engine: It executes low-level instructions generated by DML(data manipulation language) compiler. They mainly deal with solving all problems related to queries and query processing. It helps database system simplify and facilitate access to data.
2) Storage Manager (Database Manager)
The database manager is the part of database management which manages all the organizations, storage and updating of data and provides an interface between the low-level data and some programs. The storage manager is responsible for many tasks. It provides interaction with the file manager.
The important components include:
- File Manager: It manages the allocation of disk space and data structures used to represents information on the disk.
- Database Manager: It is the interface between low-level data and applications programs and queries.
- Transaction Manager: Transaction manager ensures that the database remains in a consistent(correct) state despite system failures. Examples- power failure and operating system crashes.
- DML Pre-compiler: DML pre-complier converts DDL statements which are embedded in an application program into a normal procedure calls. The pre-compiler interacts with the query processor.
- DML Compiler: It converts DDL statements to a set of tables containing metadata stored in a data directory.
DBMS Three Level Architecture
A DBMS is a buffer between the applications programs and end users and some of the database which is designed to fulfill the features of data independence. In 1975 the American national standards institute standards planning and requirement committee (ANSI-SPARC) proposed three-level architecture identified three levels of abstraction.
These three levels are sometimes to schemas or views:
1) The external or user level
This level describes the user's or applications programmer's view of the database. The same view can be shared by some programs or users.
2) The conceptual level
The conceptual level describes the view of all the data in the database. The relationships between the data and the constraints applicable to the database. This level describes a logical view of the database means a view locking implementations details.
3) The internal or physical level
This level describes the way by which the data stored in the memory and the approach by which the may be accessed. This level describes a physical view of the database
Each level is described in terms of schema i.e. a map of the database. The three-level architecture is designed in such a way that it implements data independence through two levels of mapping that between the external schema and the conceptual schema and that between the conceptual schema and the physical schema.
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