Database Management System

Lecture 2

Introduction to Database management

Learning Outcomes

• Understanding the definition of a Database management System (DBMS)

• Grasping an outline of DBMS architectures

• Understanding DBMS’s main functionalities

• Get introduced to a number of commercial

DBMSs which are widely used.

List of Topic

• DBMS definition

• DBMS functionalities

• DBMS Examples

Terminology

1 Database A collection of related information stored in a structured format

2 DBMS Database management system. A program or environment which hosts one database or more and provide support for managing information in such databases

3 Table A single store of related information. A table consists of records, and each record is made up of a number of fields

Terminology

4 SQL It stands for Structured Query Language, the standard format for commands that most database software understands

5 RDBMS Relational DBMS

DBMS definition

• DBMS is a collection of software for creating, managing and effectively searching a database.

DBMS Role Illustration

DBMS definition (con.)

• In addition a DBMS is responsible for managing application requests to a database

DBMS Three-Schema Architecture

DBMS Three-Schema Architecture (con.)

• The architecture ensures:

• the independence of logical and physical data • allowing the manipulation of data • ensure data integrity• optimize data access.

DBMS Three-Schema Architecture (con.)

1- External layer or External Schema

• It covers all the possibilities of access to data by different users.

• Access of different user groups can be done via different applications.

DBMS Three-Schema Architecture (con.)

2- Each external schema describes

• the part of the database that a particular user is interested in

• hides the rest of the database from user.

DBMS Three-Schema Architecture (con.)

2- Logical Layer or Logical Schema

• It is the general view of the data independent of individual applications and how data is stored.

• It hides the details of physical storage structures and concentrates on describing entities, data types, relationships, user operations, and constraints.

DBMS Three-Schema Architecture (con.)

3- Internal layer or Internal Schema

• Describes the physical storage structure of the database.

• The internal schema describes the complete details of data storage and access paths for the database.

DBMS Functionalities

1-Support the concepts defined in the data model in order to represent data properties.

• It usually includes the definition of specific types and the definition of consistency rules.

DBMS Functionalities (con.)

2- Make transparent data sharing between different users.

• This means that multiple users should be able to use the database concurrently and transparently

DBMS Functionalities (con.)

3- Ensure confidentiality of data

• to specify who has the right to access or modify all or part of a database.

• first requires a user identification• second requires a specification of privileges (add,

delete, update).

DBMS Functionalities (con.)

4-Ensure compliance with the consistency rules defined on the data

• after each modification on the database, all rules of consistency must be checked on all data

DBMS Functionalities (con.)

5-Being resistant to failure.

• this is to protect data against hardware failure or software whether intentional or accidental.

DBMS Functionalities (con.)

6- Possess a high storage capacity

• Thus enabling data management up to several billion bytes

• The storage units are moved from the megabyte (106) to gigabyte (109), then to terabyte (1012), peta-byte (1016), and we start talking about exabytes (1018) even zettabyte (1021).

DBMS Functionalities (con.)

7- To answer queries with a level of acceptable performance

• A query requires searching data in a database based on some conditions

• Computer power is not the only possible answer to the problems of performance

• Query optimization can be very effective to ensure

Database Examples

• Is widely used due to its ease of integration with the Apache/PHP and its good response time.

• MySQL supports only part of the standard SQL-92.

Database Examples (con.)

1. MySQL:

• It does not support native transactions, subqueries, triggers and stored procedures.

• Lacks some features compared to other DBMSs

Database Examples (con.)

2 Oracle• is a RDBMS which supports remote access to the

database hosted in it.

• It is one of the best performing DBMS with powerful

tools.

• Oracle is a RDBMS-oriented environments with heavy constraints (availability, integrity, stability, large volumes of data and high number of users, etc..).

Database Examples (con.)

3 PostgreSQL

• PostgreSQL is usable under Linux.

• Is an excellent choice to manage databases of medium size.

• It is free.

Database Examples (con.)

4 Borland Interbase

• One of its main strengths is its availability in an open source version

• A good choice to manage databases for small and medium size

Database Examples (con.)

5 Microsoft SQL Server

• SQL Server is a good choice for databases of medium size

Database Examples (con.)

6 Access

• Developed by Microsoft

• Suitable for supporting small databases (personal).

Summary

In this lesson, the following has been discussed:

• The definition of DBMS and its role.• The DBMS architecture based on the three-schema

architecture.• The main features that a robust and reliable DBMS

must have.• An outline of the most widely used DBMSs.

Exercises

• What are the three layers constituting a DBMS architecture ?

• Which layer in DBMS architecture interacts with end users or user applications ?

• List the most important features which must belong to a DBMS?

• List four widely used DBMSs?

Self-assessment

1 Search the web and find a good reference for the SQL language. Identify the SQL command that could be used to:

• Create a table.• Insert a record in a table.• Modify a data field in a table record.