This document discusses database system concepts and architecture. It covers data models, schemas, and instances. There are three categories of data models: high-level conceptual models, low-level physical models, and representational models. Schemas describe the database design while instances represent the actual data. The three schema architecture separates the internal, conceptual, and external schemas. Database languages include DDL for design, DML for manipulation, and others. DBMSs provide various interfaces and operate within a database system environment.

1. DATABASE SYSTEM CONCEPTS AND
ARCHITECTURE
Chapter 2

2. Contents
Data Models, Schemas, and Instances
Categories of Data Models
Schemas, Instances, and Database State
Three Schema Architecture and Data
Independence
Database languages
DBMS Interfaces
The Database System Environment

3. Data Model, Schemas and Instances
The data model is a collection of
concepts that can be used to describe
the structure of a database, provides
necessary means to achieve this
abstraction.
By structure of a database we mean
data types, relationships, and constraints
that hold a database.

4. Categories of Data Model
 High-level or conceptual data model
 Provide concepts that are close to the way many
users perceive data.
 Low level or physical data model
 Provides concepts that describe the details of how
data is stored in the computer
 Representational or implementational data
model
 Provide concepts that may be understood by user ,
but that are not too far removed from the way data
is organized within the computer.

5. Schemas,Instances and database State
 It is important to distinguish between the
description of the database and the database
itself.
 The description of a database is called the
database schema which is specified during
database design and is not expected to
change frequently
 The actual data in a database may change
quite frequently and is called a database state
or snapshot.

6. 3Schema Architecture

7. 3 Schema Architecture
 Internal Level has internal schema, which
describes the physical storage structure of the
database.
 Conceptual Level has conceptual schema, and
hides the physical storage structures and
concentrates on describing entities, data
types, relationships , user operations and
constraints.
 External or View Level describes a part of the
database that is particular to a group of users
interest in it and hides the rest of the database
from that user group.

8. Data Independence
Logical Data Independence
Capacity to change the conceptual schema
without changing the application programs
or external schema.
Physical data independence
Capacity to change the internal schema
without changing the conceptual schema

9. DBMS Languages
 DDL
 Used by DBA and Database designers to define
both conceptual and internal schemas.
 Storage Definition Language (sdl): used to
define the internal schema
 View Definition Language(VDL): used to
specify the user views and their mapping to
the conceptual schema.
 DML( data manipulation language): for
retrieval , insertion,deletion and modification of
the data.

10. Interfaces
Menu based Interfaces
Forms-based Interfaces
Graphical User Interfaces
Natural Language Interfaces
Interfaces for Parametric Users
Interfaces for DBA

11. The Database System Environment

12. Classification of Database
Management System
Several criteria are normally used to
classify DBMS’s
Data Model
Number of Users
Number of Sites
Cost