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Database Management System
Lecture 2
Introduction to Database management
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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.
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List of Topic
• DBMS definition
• DBMS functionalities
• DBMS Examples
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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
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Terminology
4 SQL It stands for Structured Query Language, the standard format for commands that most database software understands
5 RDBMS Relational DBMS
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DBMS definition
• DBMS is a collection of software for creating, managing and effectively searching a database.
DBMS Role Illustration
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DBMS definition (con.)
• In addition a DBMS is responsible for managing application requests to a database
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DBMS Three-Schema Architecture
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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).
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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
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DBMS Functionalities (con.)
5-Being resistant to failure.
• this is to protect data against hardware failure or software whether intentional or accidental.
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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).
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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
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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.
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Database Examples (con.)
1. MySQL:
• It does not support native transactions, subqueries, triggers and stored procedures.
• Lacks some features compared to other DBMSs
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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..).
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Database Examples (con.)
3 PostgreSQL
• PostgreSQL is usable under Linux.
• Is an excellent choice to manage databases of medium size.
• It is free.
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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
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Database Examples (con.)
5 Microsoft SQL Server
• SQL Server is a good choice for databases of medium size
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Database Examples (con.)
6 Access
• Developed by Microsoft
• Suitable for supporting small databases (personal).
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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.
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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?
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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.