Drools Rule Language (DRL) Documentation

Introduction to Drools Rule Language

• What is DRL? - A clear, approachable definition for newcomers
• Why Use DRL? - Business benefits and technical advantages
• DRL vs Other Rules Approaches - Quick comparison with alternatives (SQL, decision tables, etc.)
• Where DRL Fits in Your Architecture - How it integrates with Java applications

Getting Started with DRL

• Your First DRL Rule - Simple hands-on example with explanation
• Basic Rule Structure - The fundamental components of a rule
• Syntax Overview - Basic patterns and conventions
• Common Use Cases - Everyday scenarios where DRL shines

DRL Building Blocks

• Packages - Organization and namespaces
• Imports - Working with Java classes
• Rule Units - Modern rule organization approach
• Rule Structure - Detailed breakdown of rule components
• Rule name
• Attributes
• Conditions (when)
• Actions (then)

Working with Data in DRL

• Facts and Data Sources - Understanding the data that rules operate on
• Type Declarations - Creating and using fact types
• Data Binding - How to reference fact properties
• Accessing Properties - Different ways to extract and use data

Rule Conditions

• Pattern Matching - The foundation of rule conditions
• OOPath Expressions - Modern object traversal approach
• Constraint Operators - Comparing and evaluating data
• Complex Condition Elements - Combining conditions with and, or, exists, not, etc.
• Collections and Accumulations - Working with groups of facts

Rule Actions

• Modifying Working Memory - insert, update, delete operations
• Modifying Facts - Changing properties safely
• Executing Functions - Calling methods from rules
• Best Practices for Actions - Keeping actions clean and maintainable

Advanced DRL Features

• Rule Attributes - Controlling rule behavior
• Timers and Calendars - Time-based rule execution
• Queries - Retrieving data from working memory
• Metadata - Adding annotations to rules and facts
• Rule Inheritance - Building rule hierarchies

DRL in Practice

• Testing Rules - Strategies for verification
• Debugging Tips - Common issues and solutions
• Performance Optimization - Making rules efficient
• Integration Patterns - Connecting rules with applications

Reference

• Complete Syntax Reference - Comprehensive syntax guide
• Operator Precedence - How operators are evaluated
• Supported Functions - Built-in capabilities
• Railroad Diagrams - Visual syntax representation

Appendix

• Transitioning from Traditional to Modern Syntax
• Migrating from Other Rule Systems
• Glossary of Terms

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