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