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Structure of Database Management Systems

 

 

A database is a place/container where all the data is stored. In a database, even the smallest piece of information is data. For example, Student is a data, Course is a data, and Color is a data, Height, Weight, Food – everything is data. In short, all the living and non-living objects in this world – all their properties and attributes – can be disintegrated in the form of data.

We need to generate data in this manner so that we can perform various actions on them. If we want to record the change in water level in a well every year, we note the level on sheets of paper every month. At the end of the certain period or year, we would compare the levels to see if the discharge and recharge are in balance. If some entry is wrong or irrelevant, we can correct it or strike it off. The same procedure is adopted using a database. We would be storing all these information in the database. If we want to check the status, we would be pulling the information from the database. If we need to change any information, we can update/delete them. But all the data will be at one place - Database.

Types of Data stored in a database

In a database, we store related data in separate groups called tables. For example, Student, Teacher, Class, Subject, Employee, Department etc. form individual tables. This helps in identifying which data is stored where and under what name. It reduces the time to search for a different sets of data in a whole database. Whereas a table constituting a database contains related data, different tables may contain seemingly unrelated data. We also need to constantly update and edit the database and process queries, often by multiple users simultaneously. For this, the users need to connect to the database, and the database itself should be properly structured for such use. One can imagine a database to be similar to the human brain. How is the structure of brain? That’s a bit sophisticated, but each part of the brain is responsible for some specific tasks. Databases are designed similarly – different segments of a database management system are responsible for different tasks. These segments constitute the structure of a DBMS.

Database Management System

The Management System of a Database acts as an interface between the user and the database. The user requests the DBMS to perform various operations viz., insert, delete, update and retrieve data. Various components which perform these operations on the database constitute the structure of the DBMS. These components also help process data to produce valuable information.

Structure of DBMS

At the top level, a database is considered as shown in below diagram.  Let us see them in detail below.

 

Application & End Users

The Database Application can be considered as a user friendly web page where the user enters the requests. Here he simply enters the details that he needs and presses buttons to get the data.

The End Users are the real users of the database. They can be developers, designers, administrator or the actual users of the database.

Data Definition Language

Data Definition Language (DDL) is an instruction/command to create a database, schematic, tables, mappings etc. in the database. These are the commands used to create the objects like tables, fields, and indexes in the database for the first time. In other words, they create structure of the database.

DDL Compiler

This part of database is responsible for translating the DDL instructions into machine language and processing those commands. That means these compiler actually breaks down the command into machine understandable codes. It is also responsible for storing the metadata information like table name, space used by it, number of columns in it, mapping information etc.

DML Compiler

DML stands for Data Manipulation Language. When the user inserts, deletes, updates or retrieves records, he sends request by pressing some buttons. But for the database, this needs to be broken down to object code, which is done by this compiler. One can imagine this as when a person is asked some question, how this is broken down into waves to reach the brain!

Query Optimizer

When user makes a  request, he is least bothered how it will be communicated to the database. He is not all aware of the nuts and bolts of the database or its way of performance. Whatever be the request, the system should be able to execute it. The Query Optimizer decides the best way to execute the request received from the DML compiler. It is similar to selecting the best nerve to carry the waves to brain!

Stored Data Manager

This is also known as Database Control System. It is one the main central system of the database. It is responsible for various tasks:

  1. It converts the requests received from query optimizer to machine understandable form. 
  2. It makes actual request inside the database.
  3. It is like fetching the exact part of the brain to answer questions.
  4. It helps to maintain consistency and integrity by applying the constraints. 
  5. That means, it does not allow inserting / updating / deleting any data if it has child entry.
  6. Similarly it does not allow entering any duplicate value into database tables.
  7. It controls concurrent access.
  8. In multi-user access, it makes sure all users see the correct data.
  9. It guarantees that there is no data loss and there is no data mismatch between the transactions of multiple users.
  10. It helps to backup the database and recover the same whenever required. As for instance, when there is an unexpected error during transaction.

Data Files

This is the real estate – the real data stored in a database. The data can be stored in various formats of text, graphics, audio and video formats. It can be stored as magnetic tapes, magnetic disks or optical disks.

Compiled DML

Some of the processed DML statements (insert, update, delete) are stored in it so that if there is similar requests, it will be re-used.

Data Dictionary

Contains all the information about the database. As the name suggests, it is the dictionary of all the data items. It contains description of all the tables, view, materialized views, constraints, indexes, triggers etc.

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