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  • Mastering JBoss Drools 6
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Mastering JBoss Drools 6

Mastering JBoss Drools 6

By : Mariano De Maio, Salatino, Aliverti
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Mastering JBoss Drools 6

Mastering JBoss Drools 6

3 (1)
By: Mariano De Maio, Salatino, Aliverti

Overview of this book

Mastering JBoss Drools 6 will provide you with the knowledge to develop applications involving complex scenarios. You will learn how to use KIE modules to create and execute Business Rules, and how the PHREAK algorithm internally works to drive the Rule Engine decisions. This book will also cover the relationship between Drools and jBPM, which allows you to enrich your applications by using Business Processes. You will be briefly introduced to the concept of complex event processing (Drools CEP) where you will learn how to aggregate and correlate your data based on temporal conditions. You will also learn how to define rules using domain-specific languages, such as spreadsheets, database entries, PMML, and more. Towards the end, this book will take you through the integration of Drools with the Spring and Camel frameworks for more complex applications.
Table of Contents (13 chapters)
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Preface
Preface
What this book covers
What you need for this book
Who this book is for
Conventions
Reader feedback
Customer support
Free Chapter
1
1. Rules Declarative Nature
1. Rules Declarative Nature
What are rules?
Why do we use rules?
When should we use rules?
When not to use a rule engine
Summary
2
2. Writing and Executing Rules
2. Writing and Executing Rules
Setting up our environment
Creating our first Drools project
Writing and executing our first rule
The Rule language
Organizing our projects
Summary
3
3. Drools Runtime
3. Drools Runtime
Understanding the Drools runtime instances
KieModule configurations (KieBases, KieSessions & StatelessKieSessions)
KieScanner
Summary
4
4. Improving Our Rule Syntax
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4. Improving Our Rule Syntax
Adding external interactions with global variables
Modifying the data in the working memory
Rule attributes
Controlling loops in rules
Special Drools operations
Working memory breakdown: the from clause
Drools syntactic sugar
Decorating our objects in memory
Logical insertion of elements
Rule inheritance
Summary
5
5. Understanding KIE Sessions
5. Understanding KIE Sessions
Stateless and stateful Kie Sessions
Kie runtime components
Kie Base components
Summary
6
6. Complex Event Processing
6. Complex Event Processing
What is complex event processing?
Declaring CEP-based Rules
Event-driven architecture
Running CEP-based Scenarios
Drools CEP limitations
Summary
7
7. Human-Readable Rules
7. Human-Readable Rules
Domain Specific Languages
Decision tables
Rule templates
PMML
Summary
8
8. Rules' Testing and Troubleshooting
8. Rules' Testing and Troubleshooting
Create loosely coupled DRLs
Prefer KieHelper over a KieContainer classpath
Benefits of using globals
Debugging the left-hand side of a rule
Debugging the right-hand side of a rule
Reporting a bug in Drools
Summary
9
9. Introduction to PHREAK
9. Introduction to PHREAK
Introducing PHREAK
Special nodes in the network
Queries and backward-chaining
PHREAK improvements over RETE
Phreak Inspector
Summary
10
10. Integrating Rules and Processes
10. Integrating Rules and Processes
jBPM – the process engine
Simple business process example
Drools and jBPM: integration patterns
Persistence and transactions
Summary
11
11. Integrating Drools with our Apps
11. Integrating Drools with our Apps
Architecture considerations
Integrating with the rest of an application
CDI integration
Spring integration
Camel integration
Kie Execution Server
Kie Workbench
Drools and beyond: extending our functionality
Summary
12
Index
Index

Working memory breakdown: the from clause

We've seen how rule conditions are written. So far, all these conditions have filtered data that was inserted in our KieSession (that is, inserted in the working memory). However, in some situations, we might need to check special conditions on collections that are different from the working memory, such as attributes of some objects, global variables, or subsets of the working memory itself that we can create dynamically. To be able to do so, Drools provides the from clause, which we can be used to define a specific search space outside of the working memory.

The following rule is a simple example of how we can use the from clause to look for specific attributes:

rule "For every notebook order apply points coupon"
     when
       $o: Order($c: customer, $lines: orderLines)
       OrderLine($item: item) from $lines
       Item(name == "notebook") from $item
     then
       insert(new Coupon($c, $o, CouponType.POINTS));
   end

The previous rule looks...

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