Transcript 11. Building Information Systems

ORGANIZING DATA IN A TRADITIONAL FILE ENVIRONMENT
File Organization Terms and Concepts
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Bit: Smallest unit of data; binary digit (0,1)
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Byte: Group of bits that represents a single
character
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Field: Group of words or a complete number
ORGANIZING DATA IN A TRADITIONAL FILE ENVIRONMENT
File Organization Terms and Concepts
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Record: Group of related fields
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File: Group of records of same type
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Database: Group of related files
ORGANIZING DATA IN A TRADITIONAL FILE ENVIRONMENT
Data Hierarchy in a Computer System
Figure 7-1
ORGANIZING DATA IN A TRADITIONAL FILE ENVIRONMENT
File Organization Terms and Concepts
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Entity: Person, place, thing, event about which
information is maintained
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Attribute: Description of a particular entity
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Key field: Identifier field used to retrieve,
update, sort a record
ORGANIZING DATA IN A TRADITIONAL FILE ENVIRONMENT
Entitities and Attributes
Figure 7-2
ORGANIZING DATA IN A TRADITIONAL FILE ENVIRONMENT
Traditional File Processing
Figure 7-3
ORGANIZING DATA IN A TRADITIONAL FILE ENVIRONMENT
Problems with the Traditional File Environment
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Data redundancy
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Program-Data dependence
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Lack of flexibility
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Poor security
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Lack of data-sharing and availability
DATA REDUNDANCY
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The presence of duplicate data in multiple data
files
Different functions collect the same information
independently
May have different meanings in different parts of
the organisation
Data Redundancy
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Data Redundancy
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Staff_Branch relation has redundant data; the details of a
branch are repeated for every member of staff.
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In contrast, the branch information appears only once for
each branch in the Branch relation and only the branch
number (Branch_No) is repeated in the Staff relation, to
represent where each member of staff is located.
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Program Data Dependence
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The tight relationship between data stored in
files and the specific programs required to
update and maintain those files
Every program must describe the nature
In traditional file environment any changes to
data requires a change in all programs that
access the data
A change in tax rates for example !!
Lack of Flexibility
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Traditional File system can deliver routine scheduled
reports after a significant programming efforts
An ad hoc/ unanticipated request for information,
would require a lot of time
The information is somewhere in the system but too
expensive to locate/retrieve
Compiling the data could take weeks
Poor Security
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There is little or no control and management of
data
Data could be disseminated all over the
organisation without control
Who is accessing the data and making changes?
Lack of Data-sharing
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Lack of control over access
Hard to get hands on information
Different pieces of information in different files
and different physical locations
Since files in different locations can’t be related
hard to share or access in a timely manner
Impossible for information to flow freely
Database Technology
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DATABASE:
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A collection of data organised to serve many
applications efficiently by centralising the data and
minimising redundant data.
Historical context
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Why develop DBMS at all?
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Manage flood of data from Transaction
Processing Systems
Integrate data across organisation
“Data glare”
DBMS
A Database Management System (DBMS) is
general purpose software and hardware
facility to:
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Create, delete, reorganize, and manipulate
data in a database
Store, retrieve, share, and maintain data in
a database
Maintain relationships between the
database components
THE DATABASE APPROACH TO DATA MANAGEMENT
Database Management System (DBMS)
• Creates and maintains databases
• Eliminates requirement for data definition
statements
• Acts as interface between application
programs and physical data files
DBMS Cont’d
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Provide security and procedures relating to
privilege and access.
Authenticates the integrity of all the updates and
transactions that are carried out.
interface for the access, deletion and addition of
data and for redefining the relationships within the
database.
A DBMS is a collection of programs that manages the
database structure and controls access to the data
stored in the database.
DBMS
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Relieves the programmer or end user from the
task of understanding where and how data are
actually stored
Seperates the logical view from the physical
view
Logical View- How data perceived by end
users or business specialists
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Physical View- How data is actually organised
and structured on phsical storage
media
THE DATABASE APPROACH TO DATA MANAGEMENT
The Contemporary Database Environment
Figure 7-4
THE DATABASE APPROACH TO DATA MANAGEMENT
Types of Databases
• Relational DBMS
• Hierarchical and Network DBMS
• Object-Oriented Databases
THE DATABASE APPROACH TO DATA MANAGEMENT
Relational DBMS
• The most popular type of DBMS today for PCs
as well as for larger companies and mainframes
• Represents all data in DB as two-dimensional
tables called relations
• Similar to flat files but information in more than
one file can easily be extracted and combined
• Relates data across tables based on common
data element
• Examples: DB2, Oracle, MS SQL Server
THE DATABASE APPROACH TO DATA MANAGEMENT
Relational Data Model
Figure 7-6
THE DATABASE APPROACH TO DATA MANAGEMENT
Three Basic Operations in a Relational Database
• Select: Creates subset of rows that meet
specific criteria
• Join: Combines relational tables to provide
users with information
• Project: Enables users to create new tables
containing only relevant information
THE DATABASE APPROACH TO DATA MANAGEMENT
Three Basic Operations in a Relational Database
Figure 7-7
THE DATABASE APPROACH TO DATA MANAGEMENT
Hierarchical and Network DBMS
Hierarchical DBMS
• Organizes data in a tree-like structure
• Supports one-to-many parent-child
relationships
• Prevalent in large legacy systems
THE DATABASE APPROACH TO DATA MANAGEMENT
Hierarchical DBMS
Figure 7-8
Hierarchical
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Disadvantages
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Knowledge of physical level required
Does not support logical data independence and
does not support all physical data independence
operations
Not all problems are one-to-many types
Problems with multiple parent implementation
Problems with anomalies for parent deletion
Application development in 3GL time-consuming
Support programs are not part of the DBMS
“System created by programmers for
programmers!”
THE DATABASE APPROACH TO DATA MANAGEMENT
Network DBMS
• Depicts data logically as many-to-many
relationships
THE DATABASE APPROACH TO DATA MANAGEMENT
Network DBMS
THE DATABASE APPROACH TO DATA MANAGEMENT
Disadvantages
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Outdated
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Less flexible compared to RDBMS
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Lack support for ad-hoc and English languagelike queries
Object-Oriented databases
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Object-oriented DBMS: Stores data and
procedures as objects that can be retrieved and
shared automatically
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Object-relational DBMS: Provides capabilities
of both object-oriented and relational DBMS
DBMS Disadvantages
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DBMSs are complex;
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Need for explicit backup and control;
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Costs associated with development and
operation can be substantial;
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Consolidation of an entire business’
information resources can create a high level
of vulnerability.
Designing Databases
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Conceptual design: Abstract model of database
from a business perspective
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Physical design: How data is actually stored on
direct access storage devices
CREATING A DATABASE ENVIRONMENT
Designing Databases
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Entity-relationship diagram: Methodology for
documenting databases illustrating relationships
between database entities
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Normalization: Process of creating small stable
data structures from complex groups of data
An Entity-Relationship Diagram
Figure 7-10
An Unnormalized Relation of ORDER
Figure 7-11
An Normalized Relation of ORDER
Figure 7-12
Distributing Databases
Centralized database
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Used by single central processor or multiple
processors in client/server network
Distributing Databases
Distributed database
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Stored in more than one physical location
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Partitioned database
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Duplicated database
Distributed Databases
Figure 7-13
DATABASE TRENDS
Data Warehousing and Datamining
Data warehouse
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Supports reporting and query tools
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Stores current and historical data
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Consolidates data for management analysis and
decision making
DATABASE TRENDS
Components of a Data Warehouse
Figure 7-16
DATABASE TRENDS
Data Warehousing and Datamining
Datamining
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Tools for analyzing large pools of data
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Find hidden patterns and infer rules to predict
trends
DATABASE TRENDS
Benefits of Data Warehouses
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Improved and easy accessibility to information
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Ability to model and remodel the data
DATABASE TRENDS
Databases and the Web
Database server
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Computer in a client/server environment runs a
DBMS to process SQL statements and perform
database management tasks
Application server
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Software handling all application operations
DATABASE TRENDS
Linking Internal Databases to the Web
Figure 7-18