Logic Modeling ch5 pp.173180

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Logic Modeling(ch5 pp.173-180)

• MIS 322

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Logic Modeling

• Representing the details of the processes that
  have been identified during process modeling.
• During Analysis, logic modeling is detailed but
  generic.
• Used as a communication tool between users,
  analysts, and programmers

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Logic Modeling Approaches

• Structured English to represent process logic
• Decision Tables

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Structured English a technique for representing
the "processing" contents of a DFD process

• modified form of English used to represent
  process details
• Strong verbs to describe process action
• read, write, print, sort, move, merge, add,
  subtract, multiply, divide
• Basically, pseudo code to describe each process
  bubble at the functional primitive level
• There is no right way to write pseudo code. Just
  have a method and be consistent throughout
  document

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Structured English

• Example...
• Show processing logic for a bank's service charge
  calculation
• Process Calculate Customer Service Charge

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Example of one form of the process

• READ summary of customer monthly balances
• BEGIN IF
• IF daily-balance is lt 300 for any given day
• THEN set service-charge to 5
• ELSE set service-charge to 0
• END IF

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More complex example that includes account type

• READ customer account-type and summary of
  customer monthly balances
• SELECT CASE
• CASE 1 (account-type is NOW)
• BEGIN IF
• IF daily-balance lt 300 for any given day
• THEN set service-charge to 5
• ELSE set service-charge to 0
• END IF
• CASE 2 (account-type is REGULAR)
• BEGIN IF
• IF daily-balance lt 100 for any given day
• THEN set service-charge to greater of 3 or
  .20 times number-checks
• ELSE set service-charge to 0
• END IF
• END CASE

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Three Parts to Structured Programs

• Sequence
• Conditions
• Repetition
• Sequence we show by just listing things top to
  bottom in descending order
• Conditions and Repetition we show just like in a
  Visual Basic subprocedure

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CONDITIONAL STATEMENTS

• Conditions IF/THEN/END IF SELECT CASE / END
  CASE (or END SELECT if you like)
• BEGIN IF
• IF Quantity-in-stock is less than
  Minimum-order-quantity
• THEN GENERATE new order
• ELSE DO nothing
• END IF

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CONDITIONAL STATEMENTS

• READ Quantity-in-stock
• SELECT CASE
• CASE 1 (Quantity-in-stock greater than
  Minimum-order-quantity)
• DO nothing
• CASE 2 (Quantity-in-stock equals
  Minimum-order-quantity)
• DO nothing
• CASE 3 (Quantity-in-stock is less than
  Minimum-order quantity)
• GENERATE new order
• CASE 4 (Stock out)
• INITIATE emergency re-order routine
• END CASE

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REPETITION

• DO
• READ Inventory records
• BEGIN IF
• IF Quantity-in-stock is less than
  Minimum-order-quantity
• THEN GENERATE new order
• ELSE DO nothing
• END IF
• UNTIL End-of-file

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REPETITION

• READ Inventory records
• WHILE NOT End-of-File DO
• BEGIN IF
• IF Quantity-in-stock is less than
  Minimum-order-quantity
• THEN GENERATE new order
• ELSE DO nothing
• END IF
• END DO

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Misc. Info on Structured English

• Indent just like in programming to signify groups
  of processes
• Suggestions
• All caps for programming keywords
• cap first letter in nouns
• hyphenate phrases
• Write out conditions (less than instead of lt
  )
• Dont do tech details like initialize variables,
  etc.
• Note Figure 5-14 and 5-15 in the book are only
  appropriate if level 0 is also the functional
  primitive level

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DECISION TABLES

• a matrix representation of the logic of a
  decision
• CONDITION STUBS
• The part of a decision table that lists the
  conditions relevant to the decision.
• ACTION STUBS
• The part of a decision table that lists the
  actions that result for a given set of
  conditions.
• RULES
• The part of a decision table that specifies which
  action items are to be followed for a given set
  of conditions.

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Condition Stubs
Action Stubs
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CONSTRUCTING DECISION TABLES

• 1. Name the conditions and the values each
  condition can assume
• 2. Name all possible actions that can occur
• 3. List all possible rules
• 4. Define the actions for each rule
• 5. Simplify the decision table by removing any
  rules with impossible actions or with
  indifferent conditions

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INDIFFERENT CONDITION

• In a decision table, a condition whose value does
  not affect which actions are taken for two or
  more rules.
• Example follows this slide for reducing table by
  taking out extra columns for salaried employees

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The next 2 slides are from the book. Lets work
through reducing figure 5-18 into figure 5-19
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Complete decision table for inventory reorder
system (fig. 5-18)
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Reduced decision table for inventory reorder
system (fig. 5-19)
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When to use Structured English and when Decision
Tables?

• Use the one that is more clear or use both in
  combination
• The point is to communicate to the developers and
  the client