Lecture IS3318

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Transcript Lecture IS3318

Lecture IS3318
29/11/11
Intro to Databases
• File organization concepts
• Computer system organizes data in a hierarchy
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Field: Group of characters as word(s) or number
Record: Group of related fields
File: Group of records of same type
Database: Group of related files
• Record: Describes an entity
• Entity: Person, place, thing on which we store information
• Attribute: Each characteristic, or quality, describing entity
• E.g., Attributes Date or Grade belong to entity COURSE
The Data Hierarchy
A computer system
organizes data in a
hierarchy that starts with the
bit, which represents either
a 0 or a 1. Bits can be
grouped to form a byte to
represent one character,
number, or symbol. Bytes
can be grouped to form a
field, and related fields can
be grouped to form a record.
Related records can be
collected to form a file, and
related files can be
organized into a database.
Figure 6-1
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Problems with the traditional file environment (files maintained separately by
different departments)
• Data redundancy and inconsistency
• Data redundancy: Presence of duplicate data in multiple files
• Data inconsistency: Same attribute has different values
• Program-data dependence:
• When changes in program requires changes to data accessed by program
• Lack of flexibility
• Poor security
• Lack of data sharing and availability
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Database
• Collection of data organized to serve many applications by centralizing
data and controlling redundant data
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Database management system
• Interfaces between application programs and physical data files
• Separates logical and physical views of data
• Solves problems of traditional file environment
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Controls redundancy
Eliminates inconsistency
Uncouples programs and data
Enables organization to central manage data and data security
Human Resources Database with Multiple Views
A single human resources database provides many different views of data, depending on the information
requirements of the user. Illustrated here are two possible views, one of interest to a benefits specialist and
one of interest to a member of the company’s payroll department.
Figure 6-3
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Relational DBMS
• Represent data as two-dimensional tables called relations or files
• Each table contains data on entity and attributes
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Table: grid of columns and rows
• Rows (tuples): Records for different entities
• Fields (columns): Represents attribute for entity
• Key field: Field used to uniquely identify each record
• Primary key: Field in table used for key fields
• Foreign key: Primary key used in second table as look-up field to identify
records from original table
Relational Database Tables
A relational database organizes data in the form of two-dimensional tables. Illustrated here are tables for
the entities SUPPLIER and PART showing how they represent each entity and its attributes.
Supplier_Number is a primary key for the SUPPLIER table and a foreign key for the PART table.
Figure 6-4A
Relational Database Tables (cont.)
Figure 6-4B
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Capabilities of Database Management Systems
• Data definition capability: Specifies structure of database content, used
to create tables and define characteristics of fields
• Data dictionary: Automated or manual file storing definitions of data
elements and their characteristics
• Data manipulation language: Used to add, change, delete, retrieve data
from database
• Structured Query Language (SQL)
• Microsoft Access user tools for generation SQL
• Many DBMS have report generation capabilities for creating polished
reports (Crystal Reports)
The Database Approach to Data Management
Microsoft Access Data Dictionary Features
Figure 6-6
Microsoft Access has a
rudimentary data dictionary
capability that displays
information about the size,
format, and other
characteristics of each field
in a database. Displayed
here is the information
maintained in the SUPPLIER
table. The small key icon to
the left of Supplier_Number
indicates that it is a key field.
Some Drawbacks…
• Complexity
• A DBMS is a complex piece of software all users must fully
understand it to make use of its functionalities
• Cost of DBMS
• The cost varies significantly depending on the environment and
the functionality provided. Must take into consideration recurrent
annual maintenance costs
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Continued..
• Cost of Conversion
• Cost of converting existing applications to run on the
new DBMS and hardware. (additional training costs)
• Performance
• DBMS is written for applications in general which
means that some applications may run slower than
before
• Higher Impact of Failure
• Centralization of resources increases vulnerability of
the system
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Database Administrator
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Oversees a staff of database specialists
Final recommendations for DB design
Load and maintain DB
Establish security controls
Perform backup and recovery
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Data Administration
Database
technology
And
management
Data
Administrator
Database
Management
System
Data planning
and modelling
technology
Users
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Systems Analyst
• Or business analyst is a systems analyst that specializes
in business problem analysis and technologyindependent requirements analysis.
• A programmer/analyst (or analyst/programmer)
includes the responsibilities of both the computer
programmer and the systems analyst.
• Other synonyms for systems analyst include:
• Systems consultant
• Systems architect
• Systems engineer
• Information engineer
• Systems integrator
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Variations on the Systems Analysts
Title
• Other synonyms for systems analyst include:
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Systems consultant
Systems architect
Systems engineer
Information engineer
Systems integrator
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Role of the Systems Analyst
• Study problems and needs of an organization
• Determine best approach to improving
organization through use of:
• People
• Methods
• Information technology
• Help system users and managers define their
requirements for new or enhanced systems
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Skills of a Successful Systems
Analyst
• Analytical
• Understanding of organizations.
• Problem solving skills
• System thinking
• Ability to see organizations and information systems as systems
• Technical
• Understanding of potential and limitations of technology.
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Skills of a Successful Systems
Analyst
• Managerial
• Ability to manage projects, resources, risk and change
• Interpersonal
• Effective written and oral communication skills
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System Owners
System owners are the information system’s sponsors and chief
advocates. They are usually responsible for funding the project to
develop, operate, and maintain the information system.
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System Users
System users are the people who use or are affected by the
information system on a regular basis—capturing,
validating, entering, responding to, storing, and exchanging
data and information. A common synonym is client.
Types include:
• Internal users
• Clerical and service workers
• Technical and professional staff
• Supervisors, middle managers, and executive
managers
• Remote and mobile users (internal but disconnected)
• External users
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Stakeholders: Players in the
Systems Game
• A stakeholder is any person who has an interest in an existing
or new information system. Stakeholders can be technical or
nontechnical workers.
• For information systems, the stakeholders can be classified as:
• System owners
• System users
• Systems analysts
• System designers
• System builders
• IT vendors and consultants
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Systems Development Lifecycle
(SDLC)
• The systems development life cycle (SDLC) model
is an approach to developing an information
system or software product that is characterised
by a linear sequence of steps that progress from
start to finish without revisiting any previous
step.
• The SDLC model is one of the oldest systems
development models and is still probably the
most commonly used.
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SDLC
• Traditional systems development lifecycle
(Waterfall Model)
• SDLC - very similar to a product life cycle in
the consumer market because both a new
product and information system develop
through a number of stages.
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• The typical SDLC has the following steps:
• Initiation
• Feasibility study
• System Investigation
• System Analysis
• Systems Design
• Implementation
• Review and Maintenance
• These stages are frequently referred to as “conventional
systems analysis”, “traditional systems analysis”, “the
systems development life-cycle” or the Waterfall Model
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SDLC or The Waterfall Model
• The waterfall model describes a development
method that is linear and sequential.
• Once a phase of development is completed, the
development proceeds to the next phase and
there is no turning back.
• The advantage of waterfall development is that it
allows for departmentalisation and managerial
control.
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The Waterfall Model
Continued..
• A schedule can be set with deadlines for each
stage of development and a product can proceed
through the development process and
theoretically, be delivered on time.
• Development moves from concept, through
design, implementation, testing, installation,
troubleshooting, and ends up at operation and
maintenance.
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Initiation
Traditional SDLC
Investigation
Analysis
Design
Implementation
NO FEEDBACK!!!!
Maintenance
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SDLC
• This is now regarded as the “hard” systems approach
because of its rigid demarcation between phases.
• It has shortfalls which lead to a number of difficulties
• One major criticism of the model is that it doesn’t cater for
revisiting previous phases to correct defects.
• Feedback Loop – refinement of Waterfall Model
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Potential Strengths of the Traditional SDLC
• It has been well tried and tested
• Use of documentation standards
• Following the methodology should aid (At least to some extent)
that roll out dates, budgets and expected benefits are met.
• At the end of each phase, all parties involved in the project can
review progress.
• Much greater control on the development of computer
applications and make possible the use of project management
tools and techniques
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Potential Weaknesses of the Traditional
SDLC
• Criticisms of the methodology or perhaps of the
way it was used include:
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Failure to meet the needs of management
Unambitious systems design
Instability
Inflexibility
User dissatisfaction
Problems with documentation
Lack of control
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Potential Weaknesses of the Traditional
SDLC
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Incomplete systems
Application backlog
Maintenance workload
Problems with the “ideal” approach
It does not allow for much reflection or revision.
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Prototyping
• Building an experimental system rapidly and inexpensively for
end users to evaluate
• It will be refined until it conforms to the users’ requirements
• This is achieved through iterative development
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Advantages of Prototyping
• Useful when there is uncertainty about system requirements
or systems design
• Valuable for End-user interface design
• Encourages end-user involvement throughout the systems
development lifecycle
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Disadvantages of Prototyping
• Better suited for smaller application development.
• Prototyping may mean glossing over essential steps in the
system development.
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Application Software Packages
• A set of prewritten, precoded application software programs
that are commercially available for sale or lease
• Packages have increased as many applications are common to
many businesses: payroll, accounts and inventory control
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Advantages of Software Packages
• Most of the design work has been completed in advance
• Little extensive testing required
• Vendor support and maintenance
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Disadvantages of Software Packages
• Disadvantages may be increased with a complex system
• Required customisation and additional programming may be
expensive
• Hidden implementation costs
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End User Development
• The development of information systems by end
users with little or no formal assistance from
technical specialist
• It has been made possible by fourth generation
software tools (4GL)
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Encouraging End User Development
• The variety of application development tools
available make it easier for end user development
• Guidelines for managers to encourage intranet
website development by end users:
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Look for what makes sense
Spur creativity
Set some limits
Give managers responsibility
Make users comfortable
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Advantages to End User Development
• Improved requirements determination
• Increased user involvement and satisfaction
• Reduced application backlog
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Risks of End User Development
• It occurs outside the traditional mechanisms for
information system management and control
• Problems in ensuring that end-user developed
applications meet organisations objectives and
standards
• Rapid systems development without a formal
methodology may mean that testing and
documentation is inadequate
• Loose control of organisational data
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Definition - Outsourcing
• The practice of contracting computer centre operations,
telecommunications networks, or application development to
external vendors
• Example: Bank of Ireland, Dell
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Outsourcing
• Outsourcing has become increasingly popular as
companies believe that it is more cost effective than
maintaining their own IS staff
• Many companies are outsourcing software
procurement and support to application service
providers (ASPs) who provide and support business
application and other software via the Internet and
intranets to all of a company’s employees
workstations
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Benefits of Outsourcing
• To reduce work in the information systems
department.
• When the IS function within an organisation is
limited.
• To improve the contribution of IT to enhance
business performance.
• To create new sources of revenue.
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Benefits of Outsourcing
• To reduce work in the information systems
department
• When the IS function within an organisation is
limited
• To improve the contribution of IT to enhance
business performance
• To create new sources of revenue
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Risks associated with Outsourcing
• May loose control over IS function
• Heavy reliance on the vendor
• Proprietary information may be leaked to the competition if
sensitive data is available outside the organisation
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Sample Questions
• Discuss Porter’s Competitive Forces Model, considering the
role of information systems in gaining competitive advantage.
Illustrate your answer with diagrams and examples.
• Outline and briefly explain the stages involved on the Systems
Development Lifecycle (SDLC).