1. CHAPTER 9: Structuring System Requirements: Logic Modeling
MSIS 5653 Advanced Systems Development Dursun Delen, Ph.D. Department of Management Oklahoma State University
CHAPTER 9:
Structuring System Requirements:
Logic Modeling
1.1

2. 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
9.2

3. Structuring System Requirements in SDLC

4. Logic Modeling What is the purpose of 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
9.4

5. Logic Modeling Deliverables and Outcomes Structured English
Decision Tables
Decision Trees
State-transition diagrams
Sequence diagrams
Activity diagrams
9.5

6. Modeling Logic with Structured English
Modified form of English used to specify the logic of information processes
No specific standards
Uses a subset of English
Action verbs
Noun phrases
No adjectives or adverbs
It can be used to represent all three process types of structured programming
Sequence, Conditional Statement and Repetition
9.6

7. Modeling Logic with Structured English
Similar to programming language
If conditions
Case statements
Do-Until, While-do loops
Example:
BEGIN IF
IF Quantity-In-Stock is LESS THAN Minimum-Order-Quantity
THEN GENERATE New-Order
ELSE DO nothing
END IF
Structured English vs. Pseudo Code
9.7

8. Example: Hoosier Burger’s Inventory System
Process 4.0: Generate Payments
READ Today’s-date DO
SORT Invoice-records by Date
READ next Invoice-record
BEGIN IF
IF Date is 30 days or greater THEN GENERATE Payment
END IF
UNTIL End-of-file
Process 3.0: Generate Orders DO
READ next Invoice-item-record
BEGIN IF
If Qty-in-stock LESS THAN Min-order-qty THEN GENERATE
END IF
UNTIL End-of-file
Process 2.0: Update Inventory Used DO
READ next Stock-item-record
FIND matching Inventory-record
SUBTRACT Quantity-used
UNTIL End-of-file
Process 1.0: Update Inventory Added DO
READ next Invoice-item-record
FIND matching Inventory-record
ADD Quantity-added
UNTIL End-of-file

9. 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
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
9.9

10. Modeling Logic with Decision Tables
Example: Payroll System
9.10

11. 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
Step 1: Name the condition and all values each condition can assume
Step 2: Name all possible actions that can occur
Step 3: List all rules
Step 4: Define the actions for each rule
Step 5: Simplify the table
9.11

12. 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
9.12

13. Example: Hoosier Burger’s Inventory System

14. Modeling Logic with Decision Trees
A graphical representation of a decision situation
Consists of nodes, arcs and ovals
Each node corresponds to a choice
All possible actions are listed on the far right with ovals
Nodes and Ovals are connected with arcs
Should be read from left to right
9.14

15. Example: A Generic Decision Tree

16. Example: Payroll System
9.16

17. Deciding Among Structured English, Decision Tables and Decision Trees
Criteria
Structured English
Decision Tables
Decision Trees
Determining Conditions and Actions
Second Best
Third Best
Best
Transforming Conditions and Actions into Sequence
Checking Consistency and Completeness
9.17

18. Deciding Among Decision Tables and Decision Trees
9.18

19. 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
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
Comparison of Structured English, Decision Tables and Decision Trees
9.19

20. Problem 9.1 – Page 198
Figure 9.5 – Page 298

21. Problem 9.5 Represent the logic of the given scenario by using:
Structured English
Decision Table
Decision Tree

22. Problem 9.5 – Structured English
BEGIN IF
IF Purchase-amount is greater than $15,000.00
THEN Purchasing–Department APPROVES RFP
DO Bid Process
ELSE Purchasing-Department APPROVES Purchase
PURCHASE equipment
END IF
RETURN
(Bid Process)
SEND RFP
BEGIN IF
IF three Proposals received
AND Winning-Vendor is APPROVED
AND no Violations
THEN AWARD contract
PURCHASE equipment
ELSE DO Rebid Process
END IF
RETURN
(Rebid Process)
SEND RFP
BEGIN IF
IF Winning-Vendor is APPROVED by Purchasing
AND no Violations
THEN AWARD contract
PURCHASE equipment
END IF
ISSUE Purchase Order
RETURN

23. Problem 9.5 – Decision Table

24. Problem 9.5 – Decision Tree

25. Homework Assignment #4 Solve the following problems:
Problem 13 in Chapter 8
HINT: You may combine the “review of prescription orders by stations” in a single process (as opposed to three separate processes).
Problem 9 in Chapter 9
HINT
In Structured English section you are to calculate commission and bonus for sales reps
In Decision Table and Decision Tree sections you can limit your answer to calculating sales commission only
Assignments should be typed, professionally organized, and should have a cover page.