ch04 dbms final

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					        Chapter 4
The Database Management
     System Concept
  Fundamentals of Database Management Systems
          Chapter Objectives
   Discuss the problems encountered in a
    nondatabase information systems
    environment.

   List the five basic principles of the
    database concept.

   Describe how data can be considered to
    be a manageable resource.
                                             4-2
          Chapter Objectives
   List the three problems created by data
    redundancy.

   Describe the nature of data redundancy
    among many files.

   Explain the relationship between data
    integration and data redundancy in one
    file.
                                              4-3
          Chapter Objectives
   State the primary defining feature of a
    database management system.

   Explain why the ability to store multiple
    relationships is an important feature of the
    database approach.



                                               4-4
          Chapter Objectives
   Explain why providing support for such
    control issues as data security, backup
    and recovery, and concurrency is an
    important feature of the database
    approach.

   Explain why providing support for data
    independence is an important feature of
    the database approach.
                                              4-5
     Data Processing Systems
   Data was stored in different formats in different
    files.

   Data was often not shared among different
    programs that needed it, necessitating the
    duplication of data in redundant files.

   Little was understood about file design, resulting
    in redundant data within individual files.
                                                        4-6
     Data Processing Systems
   Files often could not be rebuilt after being
    damaged by a software error or a
    hardware failure.

   Data was not secure and was vulnerable
    to theft or malicious mischief by people
    inside or outside of the company.


                                                   4-7
     Data Processing Systems
   Programs were usually written in such a
    manner that if the way that the data was
    stored changed, the program had to be
    modified to continue working.

   Changes in everything from access
    methods to tax tables required
    programming changes.
                                               4-8
        The Database Concept
   1. Data as a Manageable Resource

   2. Data Integration and Data Redundancy

   3. Multiple Relationships

   4. Data Control Issues

   5. Data Independence

                                              4-9
       The Database Concept
   Data as a Manageable Resource - The
    creation of a data-centric environment in
    which a company’s data can truly be
    thought of as a significant corporate
    resource. A key feature of this
    environment is the ability to share data
    among those inside and outside of the
    company who require access to it.


                                                4-10
        The Database Concept
   Data Integration and Data Redundancy - The
    ability to achieve data integration while at the
    same time storing data in a nonredundant
    fashion. This, alone, is the central, defining
    feature of the database approach.

   Multiple Relationships - The ability to store data
    representing entities involved in multiple
    relationships without introducing data
    redundancy or other structural problems.

                                                       4-11
       The Database Concept
   Data Control Issues - The establishment of
    an environment that manages certain data
    control issues, such as data security,
    backup and recovery, and concurrency
    control.

   Data Independence - The establishment of
    an environment that permits a high degree
    of data independence.
                                            4-12
        Data as a Manageable
              Resource
   Information systems environment:
     Hardware
     Networks
     Applicationssoftware
     Systems software
     People
     Data



                                       4-13
        Data as a Manageable
              Resource
   Historically, data has not been the highest
    priority concern.

   As the operational, tactical, and strategic
    corporate levels became more dependent
    on information systems, data increasingly
    became recognized as an important
    corporate resource.
                                              4-14
        Data as a Manageable
              Resource
   The corporate community became
    increasingly convinced that a firm’s data
    could provide a significant competitive
    advantage to the firm.

   It became clear that data would have to be
    managed in an organized way.


                                                4-15
Data as a Manageable
      Resource




                       4-16
        Data as a Manageable
              Resource
   Needed a software utility that could
    manage and protect data.

   Data could be a critical corporate
    resource.

   Out of this need was born the database
    management system.

                                             4-17
        Data as a Manageable
              Resource
   Reengineering - data is aggressively used
    to redesign business processes.

   Electronic commerce - a database at the
    heart of every web site; allows companies
    and customers to conduct business.

   ERP systems - collections of application
    programs build around a central database.
                                            4-18
     Data Integration and Data
            Redundancy
   Data integration - the ability to tie together
    pieces of related data within an
    information system.

   Data redundancy - the same fact about the
    business environment is stored more than
    once within an information system.


                                                 4-19
Data Redundancy - Problems
   Redundant data takes up a great deal of
    extra disk space.

   If the redundant data has to be updated, it
    takes additional time to do so. This can be
    a major performance issue.

   There is the potential for data integrity
    problems.
                                                4-20
              Data Integrity
   Refers to the accuracy of the data.

   Inaccurate data leaves the whole
    information system of limited value.




                                           4-21
           Data Redundancy,
             Data Integrity




   When all copies of redundant data are not
    updated consistently, a data integrity problem
    exists.

                                                     4-22
Three Files with Redundant
            Data
   Sales file
   Customer        Customer     Customer
   Number          Name         Address
   2746795         John Jones   123 Elm Street

   Accounts Receivable file
   Customer        Customer     Customer
   Number          Name         Address
   2746795         John Jones   123 Elm Street

   Credit file
   Customer        Customer     Customer
   Number          Name         Address
   2746795         John Jones   123 Elm Street

                                                 4-23
Three Files with a Data
  Integrity Problem
 Sales file
 Customer        Customer     Customer
 Number          Name         Address
 2746795         John Jones   456 Oak Street

 Accounts Receivable file
 Customer        Customer     Customer
 Number          Name         Address
 2746795         John Jones   456 Oak Street

 Credit file
 Customer        Customer     Customer
 Number          Name         Address
 2746795         John Jones   123 Elm Street
                                               4-24
                (a) Salesperson file
Salesperson    Salesperson Commission Year Of Hire
Number         Name           Percentage
    137        Baker                 10   1995                General
    186        Adams                 15   2001
    204        Dickens               10   1998                 Hardware
    361        Carlyle               20   2001
                                                               Company
Customer
                 (b) Customer file
              Customer        Salesperson
                                                               Files
Number        Name            Number        HQ City
  0121        Main St.             137      New York
              Hardware
  0839        Jane’s Stores        186      Chicago
  0933        ABC Home             137      Los Ange les
              Stores
  1047        Acme                 137      Los Ange les
              Hardware Store
  1525        Fred’s Tool          361      Atlanta
              Stores
  1700        XYZ Stores           361      Washington
  1826        City Hardware        137      New York
  2198        Western              204      New York
              Hardware
  2267        Central Stores       186      New York
                                                                      4-25
General Hardware Company
      Combined File
 0121 Main St.         137 New York     137 Baker     10 1995
      Hardware
 0839 JaneÕsStores     186 Chicago      186 Adams     15 2001
 0933 ABC Home         137 Los Ange les 137 Baker     10 1995
      Stores
 1047 Acme             137 Los Ange les 137 Baker     10 1995
      Hardware
      Store
 1525 FredÕsTool       361 Atlanta      361 Carlyle   20 2001
      Stores
 1700 XYZ Stores       361 Washington   361 Carlyle 20 2001
 1826 City Hardware    137 New York     137 Baker   10 1995
 2198 Western          204 New York     204 Dickens 10 1998
      Hardware
 2267 Central Stores   186 New York     186 Adams     15 2001

                                                                4-26
                 Anomalies
   Typically occur in poorly structured files.

   Problems arise when two different kinds of
    data, like salesperson and customer data
    are merged into one file.




                                                  4-27
                    Anomalies
   Deletion Anomaly - e.g, if you delete a customer and that
    record was the only one for a salesperson, the
    salesperson’s data is gone.

   Insertion Anomaly - e.g., General Hardware cannot add
    data about a new salesperson the company just hired
    until she is assigned at least one customer.

   Update Anomaly - redundant data in the database file
    must be updated each place it exists when it changes



                                                           4-28
       Database Management
              System
   A software utility for storing and retrieving
    data that gives the end-user the
    impression that the data is well integrated
    even though the data can be stored with
    no redundancy at all.




                                                4-29
Multiple Relationships -
 Horizontal Solution
 Salesperson Salesperson Commission Year            Customer
 Number      Name          Percentage Of            Numbers
                                      Hire
     137     Baker               10   1995          0121, 0933, 1047, 1826
     186     Adams               15   2001          0839, 2267
     204     Dickens             10   1998          2198
     361     Carlyle             20   2001          1525, 1700
              (a) Salesperson file.

 Customer   Customer
 Number     Name                     HQ City
   0121     Main St. Hardware        New York
   0839     Jane’s Stores            Chicago
   0933     ABC Home Stores          Los Ange les
   1047     Acme Hardware Store      Los Ange les
   1525     Fred’s Tool Stores       Atlanta
   1700     XYZ Stores               Washington
   1826     City Hardware            New York
   2198     Western Hardware         New York
   2267     Central Stores           New York
                (b) Customer file.
                                                                             4-30
Multiple Relationships -
   Vertical Solution




                           4-31
           Data Control Issues




   Data security

   Backup and Recovery

   Concurrency Control
                                 4-32
        Computer Security
 A very broad topic
 Protecting the physical hardware
  environment
 Defending against hacker attacks
 Encrypting data transmitted over networks
 Educating employees on the importance of
  protecting the company’s data
 … and many more
                                         4-33
         Backup and Recovery
   Data can be lost or corrupted in any of a
    variety of ways:
    a  disaster such as a fire, a hurricane, or an
      earthquake
     hackers
     computer viruses
     poorly written application programs
     unintentional error


                                                      4-34
        Concurrency Problem
   Updates to a database can interfere with
    each other in such a way that the resulting
    data values will be incorrect.

   A database management system must be
    designed to protect its databases from
    such an eventuality.


                                              4-35
           Data Independence
   Data Dependence - if for any reason the storage
    characteristics of the data had to be changed,
    the application program itself had to be modified,
    often extensively.

   Data Independence - to have a data storage and
    programming environment in which as many
    types of changes in the data structure as
    possible would not require changes in the
    application programs that use them.

                                                    4-36
      Major DBMS Approaches
   Hierarchical - navigational

   Network - navigational

   Relational - became commercially viable in
    about 1980.

   Object-oriented - useful for a variety of niche
    applications.
                                                      4-37
       Hierarchical & Network
   Called navigational approaches because
    of the way that programs have to
    “navigate” through hierarchies and
    networks of data to find needed data.

   Developed in the 1960s and

   Somewhat similar in structure
                                             4-38
        Hierarchical & Network
   Suitable only for mainframe computers

   were an elegant solution to the
    redundancy/integration problem at the time

   Complex, difficult to work

   Now considered legacy systems

                                                 4-39
         Relational Database
   Became commercially viable in about
    1980

   Soon became the preferred DBMS
    approach and it has remained so ever
    since.



                                           4-40
             Object-oriented
   Has proven useful for a variety of niche
    applications

    It is interesting to note that some of the
    key object-oriented database concepts
    have found their way into some of the
    mainstream relational DBMSs and some
    are described as taking a hybrid
    object/relational approach to database.
                                                  4-41

				
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posted:8/31/2012
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