01-DBMS | Introduction

Information is meaningful data
It is processed, organized, and structured data
It provides context of the data and enables decision making.
Processed data that make sense to us.
Information is extracted from the data, by analyzing and interpreting pieces of data.
E.g.,you have data of all the people living in your locality, its Data, when you analyze and interpret the data and come to some conclusion that:
- There are 100 senior citizens.
- The sex ratio is 1.1.
- Newborn babies are 100.

Data is a collection of facts,
- while information puts those facts into context.
While data is raw and unorganized
- information is organized.
Data points are individual and sometimes unrelated.
- Information maps out that data to provide a big-picture view of how it all fits together.
Data, on its own, is meaningless
- When it’s analyzed and interpreted, it becomes meaningful information.
Data does not depend on information;
- however, information depends on data.
Data typically comes in the form of graphs, numbers, figures, or statistics.
- Information is typically presented through words, language, thoughts, and ideas.
Data isn’t sufficient for decision-making
- but you can make decisions based on information.

Database is an electronic place/system where data is stored in a way that it can be easily accessed, managed, and updated.
It is also used to organize the data in the form of a table, schema, views, and reports, etc.

DBMS is a software which is used to manage the database. For example: MySQL, Oracle, etc
The primary goal of a DBMS is to provide a way to store and retrieve database information that is both convenient and efficient
It provides protection and security to the database.
In the case of multiple users, it also maintains data consistency.

The major purpose of DBMS is to provide
- an abstract view of the data.
- hides certain details of how the data is stored and maintained.
- to simplify user interaction
- multiple users to access the same data with a personalized view
The collection of information stored in the DB at a particular moment is called an instance of DB
The overall design of the DB is called the DB schema
Schema is structural description of data.
- Schema doesn’t change frequently.
- Data may change frequently.

We have 3 types of Schemas: Physical, Logical, several view schemas called subschemas. Three Schema Architecture

Physical level / Internal level
- The lowest level of abstraction describes how the data are stored
- It has Physical schema which describes physical storage structure of DB.
- Talks about: Storage allocation (N-ary tree etc), Data compression & encryption etc.
- Goal: We must define algorithms that allow efficient access to data.
Logical level / Conceptual level
- The conceptual schema describes the design of a database at the conceptual level, describes what data are stored in DB, and what relationships exist among those data.
- User at logical level does not need to be aware about physical-level structures.
- DBA, who must decide what information to keep in the DB use the logical level of abstraction.
- Goal: ease to use.
View level / External level
- Highest level of abstraction aims to simplify users’ interaction with the system by providing different view to different end-user.
- Each view schema describes the database part that a particular user group is interested and hides the remaining database from that user group.
- At the external level, a database contains several schemas that sometimes called as subschema.
- The subschema is used to describe the different view of the database.
- At views also provide a security mechanism to prevent users from accessing certain parts of DB.

Data definition language (DDL)
- DDL is used to specify the database schema
- We specify consistency constraints, which must be checked, every time DB is updated.
Data manipulation language (DML)
- DML is used to express database queries and updates
- Data manipulation involves
  1. Retrieval
  2. Insertion
  3. Deletion
  4. Updating
- Query language, a part of DML to specify statement requesting the retrieval of information.
Practically, both language features are present in a single DB language, e.g., SQL language.

Apps written in host languages, C/C++, Java interacts with DB.
- E.g., Banking system’s module generating payrolls access DB by executing DML statements from the host language.
An interface in implemented between the App and DB
API is provided to send DML/DDL statements to DB and retrieve the results.
- Open Database Connectivity (ODBC), Microsoft “C”.
- Java Database Connectivity (JDBC), Java.

A person who has central control of both the data and the programs that access those data.
It works on logical level
Functions of DBA
- Schema Definition
- Storage structure and access methods.
- Schema and physical organization modifications.
- Authorization control.
- Routine maintenance
  - Periodic backups.
  - Security patches.
  - Any upgrades.

A DBMS architecture allows dividing the database system into individual components that can be independently modified, changed, replaced, and altered.
The DBMS architecture affects the performance of the database
It describes the structure and the way in which the users are connected to a specific database system.
Tier-1 Architecture
- It is the simplest architecture of Database
- The client, server & DB all present on the same machine
Tier-2 Architecture
- App is partitioned into 2-components
- Connection to DB is through network
  - SQL queries travels through network
Tier-3 Architecture
- App is partitioned into 3 logical components
- Client machine communicates with App server, and App server communicated with DB system to access data.
- Client machine –> is just a frontend
- App server –> Business logic
- T3 architecture are best for WWW Applications.
- Advantages:
  1. Scalability due to distributed application servers.
  2. Data integrity, App server acts as a middle layer between client and DB, which minimize the chances of data corruption.
  3. Security, client can’t directly access DB, hence it is more secure.

Introduction, Three Schema Architecture, DBMS Architecture, Database Languages