IT 244 Database Management System

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IT 244 Database Management System

• Lecture 1 14 / 02 /07
• Course Information
• Introduction to Database DBMS

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Topic 1 Introduction

• Evolution of Database Systems
• Data gtgt Database vs Database Management
• Compare ways DATA is organized
• Word processor (document production)
• Spreadsheets (numerical analysis)
• Traditional File Management (mini computers
  storage retrieval)
• Database (data management)
• Advantages and Disadvantages

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Ways data is organized in
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Spreadsheet Format Store data in rows and
columns

• Several things to note about the above table
• Data to be stored has uniform format. Same kind
  of information about each patient
• File size will increase as the number of patient
  records increases
• Frequently accessing the table for new or
  existing patients
• Table will be useful for all like the doctor or
  administrators
• Other people may need print out of the
  information .

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Potential problems that can arise

• Patients increase file size too so access to
  the table will become slower and slow when access
  concurrently
• Takes time to manipulate the table ie. Get
  specific information, correct an error,
  repetition of data will have to be dealt with.

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Traditional File Systems

• Information system specialist became aware of the
  problems
• So they devised ways of managing them.
• Rather then keeping data in a single large file,
• Data was separated into many different files
  according to the nature of the information to be
  stored.
• Then special software programs were written to
  manage the files.
• These programs could perform tasks such as
• add new records
• update old ones
• search for selected data within files
• and deleted unwanted records.

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Traditional File System

• Thus The data about the Hospital patients in the
  spreadsheet can be separated into the following
  files under the traditional file system.
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• File Information Stored
• Patients - Surname, First name, age, date
  admitted, date discharged
• Doctor - Surname, First name, Phone contact
• Ward - Ward number, number of rooms
• Room - Room number, beds, ward number

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Traditional method of file management
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Traditional method of file management

• Although this is an improvement over the
  spreadsheet method of storing and accessing data,
  there are still some problems.
• For instance, information about the wards is
  closely related to the information about rooms
  but they are in different files. How do you link
  them ? Often extra programming effort.
• Not every organization can afford to have a
  programmer
• Getting access to the required information often
  takes a number of steps.
• To speed up the retrieval of information you can
  create indexes for the file and/or split it up to
  avoid repetition of information and reduce the
  total size of the file.

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Disadvantages of TFM

• Since data is stored in many related files you
  can end up with
•  
• Data redundancy keeping many copies of the same
  type of data
• Data inconsistency updating some of the copies
  but not the others
• Data Dependency data access is tied to the
  program so change in data will also change in
  programs
• Excessive maintenance and upgrade costs
  Modifying the programs and structure of the data
  files require a lot of effort.

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The Evolution of Database System

• What is a database- is nothing more than a
  collection of information that exists over a long
  period of time.
• The term database refers to a collection of data
  that is managed by a DBMS

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DATABASE

• A collection of data that is managed and
  organized by a DBMS. Not all collection of data
  are databases. Databases have the following
  characteristics
•  They represent some aspects of the real world
• Hospital patients
• They are logically coherent and have some meaning
• Related in some way
• Information has some meaning.
• They are created for specific purposes.
• Information for a specific purposes.

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Database Approach
User 1
Database Management System
Patients
User 3
Doctors
User 6
Ward
User 9
Room
User 12
Data are all in one database but kept in a
separate logical units or tables. The DBMS
provides users with one interface to access the
database and present the database information to
each users according to preferences.
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Advantages of Database approach

• Data independence data items no longer tied to
  the programs
• Reduction of data redundancy and inconsistency
  Only one copy of each data item is stored
• Consolidation of data management Just one
  software program DBMS to manage access to the
  database
• Can be used in multi-user environment More
  people can used at once
• Security restrictions can be applied. Security
  features can be build into the DBMS to restrict
  and protect the data.
• The integrity of the data can be maintained
  accuracy and reliability of the data
• Standard can be enforced adhere to
  organizational policies

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What is a Database Management System (DBMS)

• A Database Management System (DBMS) is a software
  system designed to store, manage, and facilitate
  access to databases.
• In other words
• A collection of programs that enables you to
  store, modify, and extract information from a
  database. (Webopedia Computer Dictionary)

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DBMS

• DBMS is a powerful tool for creating and managing
  large amounts of data efficiently and allowing
  it to keep over long periods of time safely
• These systems are among the most complex types of
  software available.

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Capabilities that a DBMS provides

• Persistent Storage like a file system support
  very large amounts of data that exists
  independently of any processes that are using the
  data.
• - DBMS goes far beyond the file system in
  providing flexibility, such as data structures
  that support efficient access to very large
  amounts of data

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Capabilities that a DBMS provides

• Programming Interface - DBMS allows the user or
  an application program to access and modify data
  through a powerful query language
• - Again the advantage of a DBMS over a file
  system is the flexibility to manipulate stored
  data in much more complex ways than the reading
  and writing of files.

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Capabilities that a DBMS provides

• Transaction Management - DBMS support concurrent
  access to data i.e. simultaneous access by many
  distinct processes (called transactions) at once

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DBMS was expected to-

• Allow user to create new database and specify
  schema
• Give users the ability to query the data
• Support the storage of very large amount of data
• Control access to data from many users at once

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Early Database Management System

• First commercial database management systems
  appeared in the late 1960s
• These systems evolved from file system (File
  systems store data over a long period of time and
  they allow the storage of large amounts of data)

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Application of DBMS

• Airline Reservation Systems
• In this type of System, the item of data
  include-
• - Reservations by customers
• Information about flights (airports they fly
  from and to, departure and arrival time, aircraft
  flown etc)
• Information about tickets (such as prices,
  requirements and availability)

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Application of DBMS

• Banking Systems
• - Include names and addresses of customers,
  accounts, loans etc.
• - as with airlines reservation system, we expect
  many tellers and staff or customers querying and
  modifying the banks data at once

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Summary

• Course administrative matters
• How the concept of Database approach developed
• Files structure
• Users
• Database
• DBMS

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• End of Lecture

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Problems EDBMS

• File systems do not generally guarantee that data
  can not be lost if it is not backed up
• They do not support efficient access to data
  items whose location in a particular file is not
  known
• File systems do not directly support a query
  language for the data files

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Problems EDBMS

• Their support for a schema for the data is
  limited to the creation of directory structures
  for files
• File system do not satisfy concurrent access to
  files by several users or processes

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Simultaneous access

• Avoiding consequences of simultaneous access DBMS
  support
• i) isolation - the appearance that
  transactions execute one at a time
• ii) atomicity- the requirement that
  transactions either completely or not at
  all
• iii) durability- the ability to recover from
  failure or errors of many types

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Application of DBMS

• The first important applications of DBMS were one
  where-
• - Data was composed of many small items
• - Many queries or modifications were made

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Application of DBMS

• IT IS VITAL THAT SIMULTANEOUS ACCESSES TO AN
  ACCOUNT NOT CAUSE THE EFFECT OF A TRANSACTION TO
  BE LOST.
• FAILURE CANNOT BE TOLERATED.

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Relational Database Systems

• Following a famous paper written by Ted Codd in
  1970s
• Database system changed significantly
• Codd proposed that database systems should
  present the user with a view of data organized as
  tables called relations

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Relational Database Systems

• Behind the scenes, there might be a complex data
  structure that allow rapid response to a variety
  of queries. But unlike the user of earlier
  database systems, the user of a relational system
  would not be concern with the storage structure.
  Queries could be expressed in a very high-level
  language, which greatly increased the efficiency
  of database programmers

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Relational Database Systems

• Relations and Tables
• - Columns are headed by attributes which
  describe the entries in the column
• Eg. A relation named Accounts recording Bank
  Account, Balance and Type might look like

Acc No Balance Type
123 100.00 Sav
456 2000.00 Check

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Relational Database Systems

• Heading the columns are the attributes
• - Account No
• - Balance
• -Type

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Relational Database Systems

• Below the attributes are the Rows or Tuples
• The table show two tuples of the relation
  explicitly, and the dots below them suggest that
  there would be many more tuples.

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Relational Database Systems

• Suppose we want to know the balance of account
  456. We could ask this query in SQL as follows
• SELECT account No
• FROM Accounts
• WHERE accountNo 456

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Relational Database Systems

• Do NOT expect that this example is enough to make
  you an expert SQL programmer, but it should
  convey the high-level nature of the SQL
  Select-From-Where statement

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Relational Database Systems

• In principle, they ask the DBMS to
• 1. Examine all the tuples of the Relation
  Accounts mentioned in the FROM clause
• 2. Pick out those tuples that satisfy some
  criterion indicated in the WHERE clause and
• 3. Produce as an answer certain attributes of
  those tuples as indicated in the SELECT clause
• In practice, the system must optimize the
  query and find an efficient way to answer the
  query, even though the relations involved in the
  query may be very large.

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Smaller and Smaller Systems

• Originally, DBMS were large, expensive software
  running on large computers
• Size was necessary because to store large amount
  of data require large computer system
• To day many gigabytes fit on a single disk
• Size Decrease, Capacity and power increases.

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Bigger and Bigger Systems

• On the other hand, a gigabyte isnt much data.
• Corporate database often occupy hundreds of
  gigabyte
• As storage become cheaper people find new reasons
  to store greater amount of data
• Database no longer focus on storing simple data
  item (integer or short string of characters)
  but can store images, audio and video and many
  other kind of data.

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Bigger and Bigger Systems

• Handling such large database require
  technological advances
• eg. Database of modest size are today stored on
  arrays of disks which are called secondary
  storage device. (compared to main memory which is
  primary storage)
• The fact that database systems routinely assume
  data is too big to fit in main memory and must be
  located primarily on disk at all times

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Bigger and Bigger Systems

• Trends that allow database systems to deal with
  large amounts of data faster
• - Tertiary Storage-
• - tertiary storage devices perhaps storing a
  tera-byte each.
• - require much more time to access a given item
  than does a disk
• - involve transporting an object, upon which
  the desired data item is stored to a reading
  device

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Bigger and Bigger Systems

• - Parallel Computing
• - the ability to store enormous volumes of data
  is important but it would be of little use if we
  could not access large amounts of data quickly
• - thus very large databases also require speed
  enhancers.
• - parallel Computing handle such problem

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Client Server and Multi-Tier Architectures

• Client server architecture (Two-Tier) a
  request by one process (the client) are send to
  another process (the server) for execution
• N-Tier DBMS continues to act as a server, but
  its client is typically an application server.

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Client Server and Multi-Tier Architectures

• Application server in a N-Tier manage connections
  to the database, transactions, authorization and
  other aspects.
• Application Servers in turn have clients such as
  Web servers, which support end-users or other
  application.

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Summary

• The worlds of Database Systems
• The evolution of Database Systems
• Early Database Management Systems
• Relational Database System
• Smaller and Smaller Systems
• Bigger and Bigger Systems
• Client Server and Multi-Tier Architecture