DATABASE SYSTEM CONCEPTS AND
ARCHITECTURE
Chapter 2
Contents
Data Models, Schemas, and Instances
Categories of Data Models
Schemas, Instances, and Database State
Three Sc...
Data Model, Schemas and Instances
The data model is a collection of
concepts that can be used to describe
the structure o...
Categories of Data Model
 High-level or conceptual data model
 Provide concepts that are close to the way many
users per...
Schemas,Instances and database State
 It is important to distinguish between the
description of the database and the data...
3Schema Architecture
3 Schema Architecture
 Internal Level has internal schema, which
describes the physical storage structure of the
database...
Data Independence
Logical Data Independence
Capacity to change the conceptual schema
without changing the application pr...
DBMS Languages
 DDL
 Used by DBA and Database designers to define
both conceptual and internal schemas.
 Storage Defini...
Interfaces
Menu based Interfaces
Forms-based Interfaces
Graphical User Interfaces
Natural Language Interfaces
Interfa...
The Database System Environment
Classification of Database
Management System
Several criteria are normally used to
classify DBMS’s
Data Model
Number of...
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Chapter2

  1. 1. DATABASE SYSTEM CONCEPTS AND ARCHITECTURE Chapter 2
  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. 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. 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. 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. 6. 3Schema Architecture
  7. 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. 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. 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. 10. Interfaces Menu based Interfaces Forms-based Interfaces Graphical User Interfaces Natural Language Interfaces Interfaces for Parametric Users Interfaces for DBA
  11. 11. The Database System Environment
  12. 12. Classification of Database Management System Several criteria are normally used to classify DBMS’s Data Model Number of Users Number of Sites Cost
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