INFS205 Spring 2004

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INFS205 Spring 2004

• Graphical Representations
• for
• Problem Solving

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Graphical Representations

• Flowcharts
• System
• Program
• Structure
• Entity Relationships
• Data Flow Diagrams

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System Flowcharts
Overview description of basic Input-Processing-Out
put. IPO charts deal with top level. If broken
down further to describe further decomposition,
then described as HIPO or Hierarchical Input
Processing Output charts.
Input Processing
Output
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System Flowcharts
Overview description of basic Input-Processing-Out
put. IPO charts deal with top level. If broken
down further to describe further decomposition,
then described as HIPO or Hierarchical Input
Processing Output charts.
Input Processing
Output
File1 Record Field Field File2
Record Field1 Field2
Report1 Headings Body Footings File3
Record Field1 Field2
Get input record Look up rate in table Calculate
change Accumulate Totals
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Program Flowcharts

• Program flowcharts describe the logic

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Structure Chart

• Structure charts present both hierarchy and
  data(switches)

Produce Report Line
Good Input
Output Data
Good Input
Output Data
Output Report Line
Get Good Input
Process Good Data
Output line
Output Data
Good Input
Input line
Output line
Input line
Write Report Line
Format Report Line
Edit Input
Read Input
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Entity Relationship Diagrams

• Uses basic diagramming figures to define the
  complete environment for a systems. The
  components represent entities and the
  relationships between those entities.
• Basic Figures
• Relationship Lines verbs
• Entities Boxes nouns

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Relationship Symbols

• How entities relate
• 1 instance required
• 1 or no instances required
• 1 or many instances required
• 0, 1 or many instances required
• many instances required

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Relationship Symbols Cardinality
Cardinality Minimum Maximum Interpretatio
n Instances Instances
Exactly One 1
1 Zero or One 0
1 One or More 1
Many (gt1) Zero, One or more 0
Many (gt1) More than One gt1
gt1
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Relationship Diagrams

• How entities relate

Employee
Office
is assigned to is occupied by
Machine
Scheduled Maintenance
is undergoing is being done on
Customer
is assigned to is called on by
Salesperson
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Relationship Diagrams

• How entities relate

Employee
Office
is assigned to is occupied by
Number ENTITY RELATIONSHIP Number ENTITY
ONE Employee is assigned to ONE Office ONE Office
is occupied by ONE Employee
QUESTION What is the implication of the symbol
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Relationship Diagrams

• How entities relate

A (one) MACHINE is undergoing MAINTENANCE MAINTENA
NCE is being done on A (one) MACHINE
Machine
Scheduled Maintenance
is undergoing is being done on
QUESTION What is the implication of the symbol
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Relationship Diagrams

• How entities relate

One or More SALESPERSON(S) is assigned to One or
More CUSTOMER One or More CUSTOMER(S) is called
on by One or More SALESPERSON(S)
QUESTION What is the implication of the symbol
QUESTION Can you think of a fundamental business
flaw in the relationship modeled?
Customer
is assigned to is called on by
Salesperson
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Entity Symbols

• Fundamental Real entity, exists without the
  information being defined system
• Associative entity necessary because of
  information system processing
• Attributive unique identifier for repeating
  group entities

Fundamental
Associative
Attributive
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Entity RelationshipDiagrams
Patron
In the name of has has
Makes Is made for belongs to
Question Describe what is going on in this ER
Diagram
Concert/Show
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Entity Relationship Diagrams
Patron
Patron- name(PK) Address Phone Credit
Card Reservation-number(PK) Patron-name
(FK) Performance-number (FK) Concert/Show Date Tim
e Location Price Performance-number(PK) Concert/S
how Date Time Location Price Options Concert/Show
(PK) Concert details Dates Location
In the name of has has
Makes Is made for belongs to
Concert/Show
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Introduction to Data Flow Diagrams

• Overview
• defined
• symbols
• guidelines for developing
• guidelines for determining a good DFD
• DFD as agent for change
• Example

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DFD Defined

• a graphical representation of data processes
  throughout the organization
• What is a process?
• What graphical representation?
• Advantages of DFD
• system documentation
• hardware independent
• shows characteristics of the system
  (decomposition/boundary/inter-relatedness)

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Process Defined

• Collection of activities that take one or more
  kinds of input and creates an output that is of
  value Hammer Champy 1993
• The manner of combining the inputs so that the
  system will achieve a certain result.
  Schoderbeck, et.al. 1985

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Context Data Flow

• Purpose To graphically represent the data
  flowing in and out of a system along with the
  basic processing (transformation process) of the
  system.

Travel Agent
Flights Preferences
Reservation System
0.0
Travel Request
Passenger
Ticket Information
Passenger Reservation
Airline
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Data Flow Symbols
Label
Entity person, group, department, etc. that
receives or originates data. Should be labeled in
body of box.
Process an action or set of actions that takes
place to convert or transform data. Should be
numbered in top and labeled in body.
ID
Label
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Data Flow Symbols
- Label -
Label
ID
Not used in Context Flow
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Diagram Workaround

• In order to minimize the confusion created with
  the overlap of data flow lines, you may create
  duplicate instances of a data store or entity
  symbol. You must identify any duplicates as such,
  symbolically.

DS1
E2
E1
DS1
E1
DS2
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Workaround
DS 2
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DFD Development Guidelines

• Make lists
• external entities (Defines Environment)
• processes (Defines Programs or Modules)
• data stores (Defines Data)
• data flows (Defines Logic or Procedures)
• Create context diagram to define scope
• Decompose main transformation into Level 0
  diagram Add data stores to the diagram

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DFD Development Guidelines

• Decompose processes in Level 0 to primitive
  levels
• Check for Errors
• Convert Logical to Physical DFD
• Partition the final Physical DFD
• input/output screens and reports
• batch processing
• to represent programs, procedures or modules

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DFD Development Guidelines

• Name processes as imperative
• Read Input Calculate Salary Increase
• Name data stores by what is stored in them
• records, orders, forms
• Name data flows after flowing data
• records, data elements
• Name entities after what they represent
• person, organization, other system

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DFD Development Guidelines

• When do I stop decomposing the diagram?
• WHEN each process is primitive to the system in
  this context, primitive could be single decision,
  calculation, data base query AND
• WHEN each data store represents data on a single
  entity AND
• WHEN each data flow is at lowest level AND
• WHEN each transaction, interaction of the system
  is shown AND
• WHEN you, your team and the user think you have
  enough detail

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DFD Decomposition
Context Level 0 Level 1 Level 2
Primitive
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General Considerations

• Completeness - all components are accounted for
  and defined
• Consistency - are the diagrams between levels
  compatible is the inheritance valid
• Timing - DFD are timeless the system has
  never started and will never stop
• Iterative - It will not be correct the first
  time you will have to iterate

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Specific Errors to Check for

• No free standing symbols
• All inputs/outputs are inherited - balanced
• Entities are the initial and final destinations
• Data comes out of data sources (not just in)
• No process has only outputs
• No process can have only inputs

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Errors (cont)

• Data cannot move directly from one data store to
  another
• Data cannot move directly from one entity (source
  entity) to another (sink entity).
• A data flow should only occur in one direction
  read and write should be divided into two arrows.

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Problems?
Raw data
Valid Data
Customer
Customer data
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Problems?
Advising Office
Student
Validate Request
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DFD Logical or Physical

• Logical
• How business operates
• Business activities
• Collections of data
• Show business controls

• Physical
• System implemented
• Programs or module
• Physical files
• Validation actual processes for implementing
  controls

According to book, which DFD type (logical or
physical) will probably contain more symbols in
the diagram. Why?
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DFDs in Business Process Re-engineering

• Implementing a new system (or changing a current
  system) is by definition change. DFDs can help in
  that process by identifying and documenting the
  state of the system as it exists now and how it
  should exist after the implementation.

AS-IS
TO-BE
Current Logical DFD
New Logical DFD
New Physical DFD
TO-BE minus AS-IS equals the implementation
projects scope
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DFD Summary

• DFDs are a hierarchical, graphical representation
  of information system.
• When done correctly, DFDs provide
• a complete and consistent image of the system
• a communication tool
• documentation of the system
• a way to determine the scope of change

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DFD Example
Context Level
What does this DFD tell you?
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DFD Example
Level 0
What does this DFD tell you?
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Assignment

• More Information
• Lab 9-B page 463 and on disk
• DFD Assignment
• DFD and short write up
• 10 pts
• Due April 13