The Relational Database Model

Course:-MCA-II

Subject:-Database Management System

Unit:-2

Outline

Data Models, Schemas, and Instances Three-Schema Architecture Database language and Interfaces The database system environment Centralized and client/server architecture

Categories of data models

High-level or Conceptual data models: Provide concept that are close to the way many users

perceive data

Low-level or Physical data model: Provide concepts that describe the details of how data

is stored in the computer

Conceptual data models

• It uses concepts such as entities, attributes and relationships.

• Entity represents a real-world object or concept, such as employee or project

• Attribute represents some property of interest that further describes an entity, such as employee’s name or salary

• Relation among two or more entities represents an association among two or more entitles

Example of a Relation[1]

Schemas and Database State

In any data model, it is important to distinguish between the description of the data and database itself

The description of the database is called the database schema

A displayed Schema is called a schema diagram

University Database

Example of a Database Schema[2]

Schemas and Database State The data in the database at a particular moment in

time is called a database state The distinction between database schema and

database state is very important When we define a new database, we specify its

database schema only to the DBMS At this point, the corresponding database state is the

empty state with no data We get the initial state of the database when the

database is first loaded From then on, every time an update operation is

applied to the database, we get another database state

Schemas and Database State

Valid State: a state that satisfies the structure and constrains specified in the schema.

The database schema changes very infrequently. The database state changes every time the database

is updated

Schema is also called intension. State is also called extension.

Outline

Data Models, Schemas, and Instances

Three-Schema Architecture

Database language and Interfaces

The database system environment

Centralized and client/server architecture

Three-Schema Architecture

Three of four important characteristics of the database approach, listed in Ch.1 are:

Self-describing of a DB (Schema) Insulation between programs and data Support of multiple views of the data

Three-Schema Architecture : it was proposed to help achieve and visualize these characteristics

Three-Schema Architecture Defines DBMS schemas at three levels:

Internal schema at the internal level to describe physical storage structures and access paths (e.g. indexes).

Conceptual schema at the conceptual level to describe the structure and constraints for the whole database for a community of users.

External schemas at the external level to describe the various user views.

The Three-schema architecture[3]

Outline

Data Models, Schemas, and Instances

Three-Schema Architecture

Database language and Interfaces

The database system environment

Centralized and client/server architecture

DBMS Languages

The first step to create a database through DBMS is to specify conceptual and internal schemas for the database

Data Definition Language (DDL): is used by database designers to define schemas

Data Manipulation Language (DML) View Definition Language (VDL): is to specify user

views

In current DBMS, the preceding types of languages are usually not considered distinct languages

DBMS Programming Language Interfaces

Programmer interfaces for embedding DML in a programming languages:

Embedded Approach: e.g. embedded SQL (for C, C++, etc.), SQLJ (for Java)Procedure Call Approach: e.g. JDBC for Java, ODBC for other programming languagesDatabase Programming Language Approach: e.g. ORACLE has PL/SQL, a programming language based on SQL; language incorporates SQL and its data types as integral components

User-Friendly DBMS Interfaces

• Menu-based, popular for browsing on the web (URSA)

• Forms-based, designed for naïve users

• Graphics-based

• Natural language: requests in written English

• Combinations of the above

Outline

Data Models, Schemas, and Instances

Three-Schema Architecture

Database language and Interfaces

The database system environment

Centralized and client/server architecture

DBMS Component Modules

A DBMS is a complex software system

The figure showed in next slide is divide into two halves.

The top half refers to the various users of the database system

The lower half shows the internals of the DBMS responsible for storage of data and processing of transactions

Typical DBMS Component Modules[4]

Outline

Data Models, Schemas, and Instances Three-Schema Architecture Database language and Interfaces The database system environment Centralized and client/server architecture

Centralized DBMS Architecture

A centralized DBMS in which all the DBMS functionality, application program execution, and user interface processing were carried out on a single machine

Basic Client/Server Architectures

The client/server architecture was developed to deal with computer environment in which a large number of PCs, workstation, file server…

A client in this framework is typically a user machine that provides user interface capabilities and local processing

A server is a system containing both hardware and software that can provide services to the client machines.

Logical two-tier client server architecture[5]

Two-tier Architecture

This is called two-tire architectures because the software components are distributed over two systems: client and server

The emergence of the Web changed the roles of client and server, leading to the three-tier architecture

Three-tier architecture

The intermediate layer or middle layer is sometimes called the application server or Web server

Three-tier Architecture Can Enhance Security: Database server only accessible via middle tier Clients cannot directly access database server

Three-tier client-server architecture[6]

Three-tier architecture

The presentation layer displays information to the user

The business logic layer handles intermediate rules and constrains before data is passed up to the user or down to the DBMS

If the bottom layer is split into two layers (a web server and a database server), then it is a 4-tire architecture (possible to the n-tier)

REFERENCES1. http://mytechnicalarticles.files.wordpress.com/2010/07/database-

system-concepts-and-architecture.pdf

2. http://cse.hcmut.edu.vn/~c503002/Files/DANGTranTri/slides/02.pdf

3. http://mytechnicalarticles.files.wordpress.com/2010/07/database-system-concepts-and-architecture_ppt.pdf

4. Database System Concepts: Abraham Silberschatz, Henry F. Korth & S., Sudarshan, TATA Mcgraw Hill.

5. Database Systems Concepts, design and Applications 2/e, Singh S. K, PearsonEducation

6. SQL- PL/SQL, Ivan bayross, BPB Publications. 

Image References1.http://www.k9safesearch.com/search.jsp?q=relation++images+in+database+management+system&v=w

2.http://stackoverflow.com/questions/7991112/database-normalization-for-school-management-system

3.http://www.expertsmind.com/questions/draw-and-explain-the-three-level-architecture-of-database-30163918.aspx

4.http://www.expertsmind.com/questions/draw-and-DBMS Component Modules-of-database-30163918.aspx

5.http://www.studytonight.com/dbms/architecture-of-database.php

6.http://www.studytonight.com/dbms/architecture-of-database.php