Describe the architecture or structure of a DBMS and discuss the function of each of its main component?

Answer 1

STRUCTURE OF DBMS

DBMS (Database Management System) acts as an interface between the user and the database. The user requests the DBMS to perform various operations (insert, delete, update and retrieval) on the database. The components of DBMS perform these requested operations on the database and provide necessary data to the users

1. DDL Compiler -

Data Description Language compiler processes schema definitions specified in the DDL. It includes metadata

information such as the name of the files, data items, storage details of each file, mapping information and constraints etc.

2. DML Compiler and Query optimizer -

The DML commands such as insert, update, delete, retrieve from the application program are sent to the DML compiler for compilation into object code for database access. The object code is then optimized in the best way to execute a query by the query optimizer and then send to the data manager.

3. Data Manager -

The Data Manager is the central software component of the DBMS also knows as Database Control System.

The Main Functions Of Data Manager Are: --

• Convert operations in user's Queries coming from the application programs or combination of DML Compiler and Query optimizer which is known as Query Processor from user's logical view to physical file system.

• Controls DBMS information access that is stored on disk.

• It also controls handling buffers in main memory.

• It also enforces constraints to maintain consistency and integrity of the data.

• It also synchronizes the simultaneous operations performed by the concurrent users.

• It also controls the backup and recovery operations.

4. Data Dictionary -

Data Dictionary is a repository of description of data in the database. It contains information about

• Data - names of the tables, names of attributes of each table, length of attributes, and number of rows in each table.

• Relationships between database transactions and data items referenced by them which is useful in determining which transactions are affected when certain data definitions are changed.

• Constraints on data i.e.

range of values permitted.

• Detailed information on physical database design such as storage structure, access paths, files and record sizes.

• Access Authorization - is the Description of database users their responsibilities and their access rights.

• Usage statistics such as frequency of query and transactions.

Data dictionary is used to actually control the data integrity, database operation and accuracy. It may be used as a important part of the DBMS.

5. Data Files - It contains the data portion of the database.

6. Compiled DML

- The DML complier

converts the high level Queries into low level file access commands known as compiled DML.

A database system is composed of four components;

• Data

• Hardware

• Software

• Users

which coordinate with each other to form an effective database system.

1. Data -

It is a very important component of the database system. Most of the organizations generate, store and process 1arge amount of data. The data acts a bridge between the machine parts i.e.

hardware and software and the users which directly access it or access it through some application programs.

Data may be of different types.

•

User Data -

It consists of a table(s)

of data called Relation(s)

where Column(s)

are called fields of attributes and rows are called Records for tables. A Relation must be structured properly.

•

Metadata

-

A description of the structure of the database is known as Metadata.

It basically means "data about data". System Tables store the Metadata

which includes.

- Number of Tables and Table Names

- Number of fields and field Names

- Primary Key Fields

•

Application Metadata

-

It stores the structure and format of Queries, reports and other applications components.

'

2. Hardware -

The hardware consists of the secondary storage devices such as magnetic disks (hard disk, zip disk, floppy disks), optical disks (CD-ROM),

magnetic tapes etc. on which data is stored together with the Input/Output devices (mouse, keyboard, printers), processors, main memory etc. which are used for storing and retrieving the data in a fast and efficient manner. Since database can range from those of a single user with a desktop computer to those on mainframe computers with thousand of users, therefore proper care should be taken for choosing appropriate hardware devices for a required database.

3. Software -

The Software part consists of DBMS which acts as a bridge between the user and the database or in other words, software that interacts with the users, application programs, and database and files system of a particular storage media (hard disk, magnetic tapes etc.) to insert, update, delete and retrieve data. For performing these operations such as insertion, deletion and updation

we can either use the Query Languages like SQL, QUEL, Gupta SQL or application softwares

such as Visual 3asic, Developer etc.

4. Users - Users are those persons who need the information from the database to carry out their primary business responsibilities i.e.

Personnel, Staff, Clerical, Managers, Executives etc. On the basis of the job and requirements made by them they are provided access to the database totally or partially.

The various types of users which can access the database are:-

•

Database Administrators (DBA)

•

Database Designers

•

End Users

•

Application Programmers