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

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

Structuring System Requirements in SDLC

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

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

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

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

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

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

Modeling Logic with Decision Tables Example: Payroll System 9.10

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

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

Example: Hoosier Burger’s Inventory System

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

Example: A Generic Decision Tree

Example: Payroll System 9.16

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

Deciding Among Decision Tables and Decision Trees 9.18

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

Problem 9.1 – Page 198 Figure 9.5 – Page 298

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

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

Problem 9.5 – Decision Table

Problem 9.5 – Decision Tree

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.