Process Descriptions: 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. Chapter 8 © 2008 by Prentice Hall 1 1

Logic Modeling Text-based process descriptions provide more information about the process than the DFD alone If the logic underlying the process is quite complex, more detail may be needed in the form of logic model: Structured English Decision trees Decision tables

Structured English Structured English: modified form of English language used to specify the logic of information system processes. No single standard. Typically relies on action verbs and noun phrases and contains no adjectives or No specific standards. Chapter 8 © 2008 by Prentice Hall 3 3

Structured English Common Statements Example Action Statement Profits = Revenues - Expenses Generate Inventory Report Add Product record to Product Data Store If Statement IF Customer Not in Customer Data Store THEN Add Customer record to Customer Data Store ELSE Add Current Sale to Customer’s Total Sales Update Customer record in Customer Data Store For Statement FOR all Customers in Customer Data Store, do Generate a new line in the Customer Report Add Customer’s Total Sales to Report Total Case Statement CASE If Income < 10,000: Marginal tax rate = 10% If Income < 20,000: Marginal tax rate = 20% If Income < 30,000: Marginal tax rate = 31% If Income < 40,000: Marginal tax rate = 35% ELSE Marginal tax rate = 38% ENDCASE

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Structured English Chapter 8 © 2008 by Prentice Hall 6

Decision Trees Graphical way of depicting if-then-else logic

Decision Tables Represent very complex processes with multiple decision rules Decision table: a matrix representation of the logic of a decision which specifies the possible conditions for the decision and the resulting actions. Best used for complicated decision logic. Chapter 8 © 2008 by Prentice Hall 8 8

Decision Tables Chapter 8 © 2008 by Prentice Hall 9 9

Decision Tables Condition stubs: that part of a decision table that lists the conditions relevant to the decision. Action stubs: that part of a decision table that lists the actions that result for a given set of conditions. Chapter 8 © 2008 by Prentice Hall 10 10

Decision Tables Rules: that part of a decision table that specifies which actions are to be followed for a given set of condition. Indifferent condition: in a decision table, a condition whose value does not affect which actions are taken for two or more rules. Chapter 8 © 2008 by Prentice Hall 11 11

Decision Tables Procedure for Creating Decision Tables Name the condition and the values that each condition can assume. Name all possible actions that can occur. List all possible rules. Define the actions for each rule. Simplify the table. Chapter 8 © 2008 by Prentice Hall 12 12

Decision Tables Chapter 8 © 2008 by Prentice Hall 13 13

Deciding Among Structured English and Decision Tables Criteria Structured English Decision Tables Determining Conditions and Actions Second Best Third Best Transforming Conditions and Actions into Sequence Best Checking Consistency and Completeness Chapter 8 © 2008 by Prentice Hall 14 14