#### Overview of this book

Free Chapter
Part 1:The Problem with Excel, and Why Rule-Based AI Can Be the Solution
Chapter 1: Wrestling with Excel? You Are Not Alone
Chapter 2: Choosing an AI and Business Rules Engine – Why Drools and KIE?
Part 2: Writing Business Rules and Decision Models – with Real-Life Examples
Chapter 4: More Decision Models, Business Rules, and Decision Tables
Chapter 5: Sharing and Deploying Decision Models Using OpenShift and GitHub
Chapter 6: Calling Business Rules from Excel Using Power Query
Part 3: Extending Excel, Decision Models, and Business Process Automation into a Complete Enterprise Solution
Chapter 7: Using Business Rules in Excel with Visual Basic, Script Lab, or Office Scripts
Chapter 8: Using AI and Decision Services Within Power Automate Workflows
Chapter 9: Advanced Expressions, Decision Models, and Testing
Part 4: Next Steps in AI, Machine Learning, and Rule Engines
Chapter 10: Scaling Rules in Business Central with Docker and the Cloud
Chapter 11: Rules-Based AI and Machine Learning AI – Combining the Best of Both
Chapter 12: What Next? A Look inside Neural Networks, Enterprise Projects, Advanced Rules, and the Rule Engine
Index
Other Books You May Enjoy
Appendix A - Introduction to Visual Basic for Applications
Appendix B - Testing Using VSCode, Azure, and GitHub Codespaces
Appendix C - Troubleshooting Docker

# A tour of the UI

Our `Hello World` example is a great start, but obviously, Decision Models and rules can do so much more. Let’s expand our `Hello World` example a bit more and explore KIE Sandbox along the way.

To start, you may have noticed a blue box marked Problems at the bottom right of the KIE Sandbox decision model screen, as shown in Figure 3.18:

Figure 3.18 – Issues highlighted by KIE

This screen shows when you click on the Problems button. But what do these messages mean? What is a variable, and how can it be missing a type reference? Let’s explain what variables and types are.

## What is a variable?

You have almost certainly typed a formula into Excel to add two cells together – something such as `= A1+B1`. In this case, you’re telling Excel to go to the box (cell) named A1, take the value found there, and add it to the value that Excel finds in box (cell) B1. If the values in the boxes (cells) change, the...