Drools is a business rule management system (BRMS) with an inference based engine, using an enhanced implementation of the Rete algorithm. Business rules implementations are aimed mostly at developers. However, it is sometimes needed that these rules are readable and understandable by the business analysts. Ideally, they should be able to change rules or even write new ones. Decision table as a form of human-readable rules involve business analysts in creation and maintenance of rules. Managing rules in a spreadsheet format is very applicable for business analysts since they already use them. An important aspect of business rules is their readability and user friendliness. Looking at a rule, you should immediately have an idea of what it is about.

1. Dragan Juričić, Privredna banka Zagreb

2. Introduction to “business rules”
High level overview of JBoss Drools
Decision tables
Discussion of benefits and downsides

3. Business Rules

4. Basic problem: how to model “business logic”
try to automate all kinds of business process
process and decisions are not very well
representded using traditional programing
language such as Java or C#
Drools – makes the process of implementing
rules quicker and handles complexity

5. Rule engine is a piece of software, which having some
knowledge is able to perform conclusions
Type of Expert System
Two types of rules:
“Production (or Inference) Rules”
If x, then y
Often stateless
“Reaction Rules” (Complex Event Processing)
Wait for set of events
Stateful

6. Rules consist of conditions and actions, which are executed
when their conditions are true
Conditions for above rule:
Object type condition - Applicant Object Type
Field condition - age < 18
Matching patterns against the inserted data
6
rule "Is of valid age"
when
$a : Applicant(age <18) Condition
then
$a.setValid( false); Action
end
public class Applicant {
private String name;
private int age;
private boolean valid;
//getter and setter methods
}

7. 7
JBoss Drools

8. 8
“A common platform to model and govern the business logic of the
enterprise.”

9. Core Drools product
Has an enhanced and optimized implementation of
the Rete algorithm for object oriented systems
called as ReteOO
Higher memory consumption for increased speed
Forward chaining rule interpreter : “data driven”
9

10. Technical Rule Language (Drools Rule Language –
DRL)
mostly aimed for developers
Human-readable rules
Custom Domain Specific Languages (DSL)
Guided Editor
DecisionDecisionDecisionDecision TableTableTableTable
XML
10

11. Decision Tables

12. Excel XLS based
Tabular representation of decisions
Compact way to model large sets of related rules
12

13. 13
rule "Interest Calculation_16"
when
$a:Account(type == Account.Type.SAVINGS,
currency == "EUR", balance >= 100 && < 1000,
monthsBetweenStartAndEndDate >= 1 && < 3)
then
$a.setInterestRate(new BigDecimal("3.00"));
end

14. Advantages of a decision tables
It is easy to read and understand
Refactoring is quicker (change conditions across group of rules)
Involve “business users” in creation & maintenance
Many businesses already use spreadsheets for managing data
Any formatting available in a spreadsheet editor can be applied
Disadvantages of a decision table
XLS is a binary format which makes version management more
difficult
It can be awkward to debug these rules
14

15. 15

16. 1 DecisionTableConfiguration dtableconfiguration =
2 KnowledgeBuilderFactory.newDecisionTableConfiguration();
3 dtableconfiguration.setInputType(DecisionTableInputType.XLS);
4 dtableconfiguration.setWorksheetName("Tables");
5
6 KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();
7 kbuilder.add(ResourceFactory.newClassPathResource("SearchCase.xls"),
8 ResourceType.DTABLE, dtableconfiguration);
9
10 if (kbuilder.hasErrors()) {
11 for (KnowledgeBuilderError err : kbuilder.getErrors()) {
12 System.out.println("Drools error: " + err.getMessage());
13 }
14 }
15 KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase();
16 kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());
17
18 StatelessKnowledgeSession ksession = kbase.newStatelessKnowledgeSession();
19 ksession.execute(Iterable p_objects);
16

17. Discussion

18. Large set of rules, with complex branching
Rules likely to change over time, likely out
of sync with code changes
Involve “business users” in creation &
maintenance of rules

19. Separates “business logic” from application
code
“Hot” changes of rules (no recompile)
Improved performance for large rule sets
Communicates rules more clearly than Java
code

20. New tool
Learning curve
Extra point of failure
Overhead
Not practical for small rule sets

21. http://www.jboss.org/drools/
http://en.wikipedia.org/wiki/Drools
http://docs.jboss.org/drools/release/5.5.0.Final/droolsjbpm-
introduction-docs/html_single/index.html
http://technicalmumbojumbo.wordpress.com/2009/03/28/jb
oss-drools-decision-tables/
http://www.packtpub.com/article/human-readable-rules-
with-drools-jboss-rules-part1
http://docs.jboss.org/drools/release/5.5.0.Final/droolsjbpm-
introduction-docs/html_single/index.html
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