Information Systems System Analysis 421 Class Eight

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Information Systems System Analysis 421Class
Eight
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Class Exercise

• A. BadMouth Press works with several different
  authors who write the books it publishes. Some
  authors have written only one book, while others
  have written many also, some books are co-author
  by multiple authors. BadMouth also works with
  multiple printers each book, though, is printed
  by only one printer. An editor at BadMouth Press
  works with several authors at a time, editing and
  producing their book projects it is the editor's
  job to turn over the final camera-ready copy to
  the printer when the manuscript has been copy
  edited and typeset.

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Class Exercise
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Class Exercise
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Class Exercise
A. SkyHigh Airlines has three major resources
airplanes, pilots, and crew members. Pilots and
crew members have respective home bases, which
they return at the end of an assigned flight. A
flight must have at least one pilot and one or
more crew members attached to an airplane. Each
airplane has a maintenance base.
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Class Exercise
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Class Exercise
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Learning Objectives

• Use Structured English as a tool for representing
  steps in logical processes in data flow diagrams
• Use decision tables and decision trees to
  represent the logic of choice in conditional
  statements
• Select among Structured English, decision tables,
  and decision trees for representing processing
  logic
• Logic modeling and Internet applications

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Logic Modeling

• Data flow diagrams do not show the logic inside
  the processes
• Logic modeling involves representing internal
  structure and functionality of processes depicted
  on a DFD
• Logic modeling can also be used to show when
  processes on a DFD occur

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Logic Modeling

• Deliverables and Outcomes
• Structured English
• Decision Tables
• Decision Trees
• State-transition diagrams
• Sequence diagrams
• Activity diagrams

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Modeling Logic with Structured English

• Modified form of English used to specify the
  logic of information processes
• Uses a subset of English
• Action verbs
• Noun phrases
• No adjectives or adverbs
• No specific standards

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Modeling Logic with Structured English

• Similar to programming language
• If conditions
• Case statements
• Figure 9-3 shows Structured English
  representation for Hoosier Burger

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Modeling Logic with Decision Tables

• A matrix representation of the logic of a
  decision
• Specifies the possible conditions and the
  resulting actions
• Best used for complicated decision logic

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Modeling Logic withDecision Tables

• Consists of three parts
• Condition stubs
• Lists condition relevant to decision
• Action stubs
• Actions that result from a given set of
  conditions
• Rules
• Specify which actions are to be followed for a
  given set of conditions

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Modeling Logic with Decision Tables

• Indifferent Condition
• Condition whose value does not affect which
  action is taken for two or more rules
• Standard procedure for creating decision tables
• Name the condition and values each condition can
  assume
• Name all possible actions that can occur
• List all rules
• Define the actions for each rule
• Simplify the table

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Figure 9-4Complete decision table for payroll
system example
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Modeling Logic with Decision Trees

• A graphical representation of a decision
  situation
• Decision situation points are connected together
  by arcs and terminate in ovals
• Two main components
• Decision points represented by nodes
• Actions represented by ovals

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Modeling Logic with Decision Trees

• Read from left to right
• Each node corresponds to a numbered choice on a
  legend
• All possible actions are listed on the far right

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Figure 9-9Decision tree representation of the
decision logic in the decision tables in Figures
9-4 and 9-5, with only two choices per decision
point
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Deciding Among Structured English, Decision
Tables and Decision Trees
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Structure English

• Modified English
• No formal dictionary
• Just nouns and verbs (no adjectives or adverbs)
• Used for describing processing logic
• Common referred to as psuedocode but is kept
  simple so end users can follow

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Logic Models

• Structured English
• relies on action verbs and nouns
• Decision tables
• Decision trees

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Structure English

• Build it from the DFD describing each of the DFD
  processes
• Only need to do for your lowest level DFDs
• Describes how the process changes the inputs to
  outputs
• Verify that Structured English uses the same
  inputs and outputs as your DFD

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Structure English

• We have salaried and hourly employee
• Salary employees get paid overtime after 50 hours
• Hourly employees are paid straight pay
• If they work over 40 hours they get time and a
  half
• If they work second shift they get a differential
• If they work third shift they get hazard pay
• If they work Sunday but did not work 40 hours for
  the week they get double time
• If they work Sunday and did work 40 hours they
  get overtime
• If they were on vacation that counts as working
• If they drive a blue car and have green eyes they
  get no pay

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Structure English
Salary status
Hours worked
Hours worked
Employee Salary status
Salary status
Paycheck amount
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Structure English

• Process 2.1
• read payroll information
• until employee found
• get salary status
• Process 2.2
• read payroll information
• until employee found
• get hours worked
• get pay rate

• Process 2.3
• if salary status is salaried, then pay at pay
  rate
• else case
• worked lt40 hours
• do pay rate hours
• do absence report routine
• worked 40 hours
• do pay rate hours
• worked gt40 hours
• do pay (rate 40)
• ((hours - 40) rate 1.5)
• Process 2.4
• collect absence reasons
• produce report
• send report

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Decision Tables

• A matrix representation of the logic of a
  decision.
• Three constructs
• Condition Stubs the part of the table that lists
  conditions relevant to the decision or policy
• Action Stubs the part of the table that lists
  the action results for a given set of conditions
• Rules the part of the decision table that
  summarizes the set of actions to be followed
• Advantage of decision tables
• Easier to understand
• Cover all conditions
• Easier to translate into computer code
• More clearly thought out

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Decision Tables

• A graphical technique that depicts decisions or
  choices.
• Steps in decision tables
• Identify the condition and values
• Determine the maximum number of rules
• Identify the possible actions
• Enter all possible rules
• Define the action for each rule
• Verify the policy
• Simplify the decision tree

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Figure 9-4Complete decision table for payroll
system example
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Summary

• Several methods of logic modeling
• Structured English
• Primarily communication technique for analysts
  and users
• Decision Tables
• Conditions are listed in condition stubs
• Possible actions are listed in action stubs
• Rules link conditions with actions

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Summary

• Decision Tables
• Lists all possible rules
• Decision Trees
• Conditions are portrayed by decision points
• Values are represented by paths between decision
  points and ovals that contain actions

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Summary

• Comparison of Structured English, Decision Tables
  and Decision Trees
• Most studies show that decision trees are best
  for many criteria
• There is no best technique
• Analyst must be proficient in all three

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