Logic Modeling

Learning Objectives Use Structured English as a tool for representing steps in logical processes in data flow diagrams 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 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 Select among Structured English, decision tables, and decision trees for representing processing logic

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

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

Logic Modeling Techniques

Deciding Among Structured English, Decision Tables and Decision Trees Criteria Structured English Decision Tables Decision Trees Determining Conditions and Actions 2 nd 3rd1st Transforming Conditions and Actions into Sequence 1st3rd1st Checking Consistency and Completeness 3rd1st1st

Practical Considerations ► Know all 3 techniques.  If you only know how to use a hammer, every problem looks like a nail. ► Structured English may be best when  The logic is very simple  The goal is to communicate with users ► Decision Tables may be best when  The sequence of the decision criteria (the questions you would ask) is not important  Consistency, completeness and flexibility/scalability are important  You want to depict a large amount of data in a small amount of space ► Decision Trees may be best when  The sequence of the decision criteria is important.

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

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