The document discusses database system concepts including architecture, schema, and instances. It describes 1-tier, 2-tier, and 3-tier architectures. A 1-tier architecture has the client, server, and database on one machine. A 2-tier architecture separates the presentation and data layers across two machines. A 3-tier architecture introduces an application layer between the presentation and data layers. The schema defines the database structure while instances represent the stored data at a point in time.

1. Database system concept and architecture, data
model schema and instances

2. Database System Architecture
• The design of a DBMS depends on its architecture.
• It can be centralized or decentralized or hierarchical.
• DBMS architecture helps in design, development,
implementation, and maintenance of a database.
• A database stores critical information for a business.
• The architecture of a DBMS can be seen as either single tier or
multi-tier.
• DBMS architecture depends upon how users are connected to
the database to get their request done.

3. Types of DBMS Architecture

4. 1 Tier Architecture
• The simplest of Database Architecture are 1
tier where the Client, Server, and Database all
reside on the same machine.
• Anytime you install a DB in your system and
access it to practice SQL queries it is 1 tier
architecture.
• But such architecture is rarely used in production.
• The 1-Tier architecture is used for development
of the local application, where programmers can
directly communicate with the database for the
quick response.

5. 2 Tier Architecture
A two-tier architecture is a database architecture where
1. Presentation layer runs on a client (PC, Mobile, Tablet, etc)
2. Data is stored on a Server.
The 2-Tier architecture is same as basic client-server.
In the two-tier architecture, applications on the client end can directly
communicate with the database at the server side. For this interaction, API's
like: ODBC, JDBC are used.
The user interfaces and application programs are run on the client-side.
The server side is responsible to provide the functionalities like: query
processing and transaction management.
To communicate with the DBMS, client-side application establishes a
connection with the server side.

7. 3 Tier Architecture
3-tier schema is an extension of the 2-tier architecture. 3-tier architecture has
following layers
1. Presentation layer (your PC, Tablet, Mobile, etc.)
2. Application layer (server)
3. Database Server
This DBMS architecture contains an Application layer between the user and the
DBMS, which is responsible for communicating the user's request to the DBMS
system and send the response from the DBMS to the user.
The application layer(business logic layer) also processes functional logic,
constraint, and rules before passing data to the user or down to the DBMS
Three tier architecture is the most popular DBMS architecture.

9. The goal of Three-tier architecture is:
To separate the user applications and physical database
Proposed to support DBMS characteristics
Program-data independence
Support of multiple views of the data

10. Data Schema and Instances
Schema is the overall description
of the database.
The basic structure of how the
data will be stored in the
database is called schema.
It defines how the data is
organized and how the relations
among them are associated.
It formulates all the constraints
that are to be applied on the
data.

11. • The data which is stored in the database at a particular
moment of time is called an instance of the database.
• The instances can be changed by certain CRUD operations as
like addition, deletion of data.
• It may be noted that any search query will not make any kind
of changes in the instances.

12. Schema Instance
It is the overall description of the database.
It is the collection of information stored in a
database at a particular moment.
Schema is same for whole database.
Data in instances can be changed using addition,
deletion, updation.
Does not change Frequently. Changes Frequently.
Defines the basic structure of the database i.e how
the data will be stored in the database.
It is the set of Information stored at a particular
time.

13. Three schema architecture
The three schema architecture is
also called ANSI/SPARC
architecture or three-level
architecture.
This framework is used to describe
the structure of a specific
database system.
The three schema architecture is
also used to separate the user
applications and physical
database.
The three schema architecture
contains three-levels.
It breaks the database down into
three different categories.

14. Mapping is used to transform the request and response between various
database levels of architecture.
Mapping is not good for small DBMS because it takes more time.
In External / Conceptual mapping, it is necessary to transform the request from
external level to conceptual schema.
In Conceptual / Internal mapping, DBMS transform the request from the
conceptual to internal level.

15. Internal Level
• The internal level has an internal schema which describes the physical storage
structure of the database.
• The internal schema is also known as a physical schema.
• It uses the physical data model. It is used to define that how the data will be
stored in a block.
• The physical level is used to describe complex low-level data structures in
detail.

16. Conceptual Level
• The conceptual schema describes the design of a database at the conceptual
level.
• Conceptual level is also known as logical level.
• The conceptual schema describes the structure of the whole database.
• This schema hides information about the physical storage structures and
focuses on describing data types, entities, relationships, etc.
• In the conceptual level, internal details such as an implementation of the data
structure are hidden.
• Programmers and database administrators work at this level.

17. External Level
• 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.
• An external schema is also known as view schema/view level.
• Each view schema describes the database part that a particular user group is
interested and hides the remaining database from that user group.
• The view schema describes the end user interaction with database systems.
• There may be "n" number of external views for each database.

18. Advantages Database Schema
You can manage data independent of the physical storage
Faster Migration to new graphical environments
DBMS Architecture allows you to make changes on the presentation level
without affecting the other two layers
As each tier is separate, it is possible to use different sets of developers
It is more secure as the client doesn't have direct access to the database
business logic
In case of the failure of the one-tier no data loss as you are always secure by
accessing the other tier

19. Disadvantages of Database Schema
Complete DB Schema is a complex structure which is difficult to
understand for every one
Difficult to set up and maintain
The physical separation of the tiers can affect the performance of
the Database