database introduction
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Introduction
Database integral part of our day to day life Collection of related database Database Management System : software
managing and controlling access to the database.
Database system : collection of application interracting with database
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Example of use of database systemsA database is accessed when :
Purshasing in a supermarket ( item price) Purchase using credit cards ( valid cards) Inquiries about a holliday (flight details) Make a loan (library) Rent video ( detail info on each video) Online bookstore( book details)
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Sample data
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Dtabase in the dev cycleProject
Identifcation and Selection
ProjectInitiation
and Planning
Analysis
Logical Design
PhysicalDesign
Implementation
Maintenance
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Database A repository of data simultaneously used by many
users (a shared ressource). Collection of logically related data. Description of this data (data dictionary) BDMS
Software interracting with : Users Application programs database
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BDMSSoftware interracting with : Users Application programs Database
DBMS allows users (using a query language): Insert Update Delete Retrive data from DB
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Database application programsComputer program that allow users to interact with the DB through DBMS.
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DBMS environment Hardware :Computer systems that DBMS and
application programs run on. Software: DBMS,application programs, operating
system, network software(if DBMS used over network).
Data ( operational data and meta-data) Procedures: instruction and rules that govern use of
database People: DB designer, administrators , programmers
and end users
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Database environment
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DBMS architecture2 layer architecture Client-Server The client that runs the application and the server that
handles the database back-end Multiple users able to access the DB simultanousely. Server is processing data while the client for business
logic and presentation.
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2-Tier Architecture
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DBMS architecture
3 layer architecture User Interface layer ( runs on the user´s client) Business logic (middle layer) and data processing
layer. Runs on a server called ”application server”. DBMS ( store data ) , may run on a separate server
called ”database server”
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3 layer architecture advantages Thin client (less hardware) , client only handling
presentation logic.This means a little communication needed between the client(browser) and the middle tier.
Separating the core business logic from the database functions
Modularity : Easy to modify or replace one tier without affecting the other tiers
Easier load balancing Maps quite naturally to the web environment Security : middle tier protecting the DB. Scalabale : add as many middle tier as needed
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Functions of a DBMS
Data storage , retrieval and update
A user-accessible Catalog
Hold data about the structure of database , users , applications and so on
Transaction support
Ensure that all the updates are made or that none of them are made
Concurrency control services
Enable many users to access shared data concurrently
Recovery services
When transaction fails, DB revovered to a consistent state
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Functions of a DBMS
Autorization services
Only special part could have access to info
Support for data communication
Terminal at remote locations can communicate with host of DBMS through network
Integrity Services
Stored data are consistent and correct
Services to promote Data Independence
Utility Services
Utility program help manage the DB effectively
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Advantages of DBMS Control of data redundancy (duplication)
Eliminate redundency where possible ,
Data consistency Data stored in more than once , system can ensure that all copies
of the data are kept consistent
Sharing of data By all authorized users
Improved data integrity Rules that DB is not permitted to violate User define data and DBMS enforce it
Improved maintenance through data independence Make application immune to changes in data description