drools

Geoffrey De Smet

Why do I need
the Guvnor BRMS?

Guvnor agenda

Use cases

My business requires domain expertise

My business rules change often

Auditable and reproducible

Future improvements

Use cases

I have hammer,
so every problem is a nail?

The myth

BecauseDrools can fulfil business rules

Drools is Turing complete

we should write the entire business layer in Drools?No!

Not imperative like Java, Scala, Groovy, ...

Declarative like RegEx, SQL, JPA-QL, Easier to read, better at scaling

Extract business decisions in Drools that either:Require schooled domain expertise

Change often/fast

Use cases

Financial decisionsMortgages acceptance and interest calculation

Insurances acceptance and fee calculation

Price calculationsPhone/Telecom bills

DiagnosticsPossible diseases based on symptoms

Complex validationCar parts selection

Not a good use case: an XML parserUse Java code for that

Mortgages example

Developers don't like
data input from spreadsheets

Before App 1.0: Mortgages rules in a spreadsheetWhich version/copy of the spreadsheet file?

Which field has the result our application need?

Version 1

Version 2

Mortgage experts like
the flexibility of spreadsheets

Since App 1.0: Mortgages rules in source codeChanging business rules not flexible enoughBusiness rules are hard coded in Java

Invalid: must be a number

Flooded with new improvement requests:when income below 500

when income below 1000 and age above 50

when income below 1% of mortgage amount

Data model in Guvnor

Import POJO jar

or Design the model in Guvnor:

Mortgage experts like the flexibility of Guvnor

App 2.0: Mortgage rules in Guvnor repositoryFlexible like spreadsheetBut fields clearly defined

No spreadsheet versions/copiesAuditable

My business requires
domain expertise

Only mortgage managers
understand mortgage rules

Schooled domain expertise

Are we, the developers, domain experts?Yes, we've been working in this company for year(s).

Do we haveuniversity's degree in economics? No

participated in mortgages conferences/courses? No

years of mortgage customer experience? No

Do we have a clue when the mortgage rules need to change? No

Are we, the developers, domain experts? NoMortgage manager is the domain expert

Domain experts can not read/write Java source code

Communication problemDomain expert can not read it:

for (Mortgage m : mortgages) { for (Applicant a : m.getApplicants()) { if (a.getAge() > 70) { boolean existsGuarantor = false; for (Guarantor g : m.getGuarantors() { if (g.getAge < 60) { existsGuarantor = true; } } // Will they spot the bug in this code? if (existsGuarantor) { m.setApproved(false); } } }}

DRL scales better than this Java code

Domain experts can read/write DRL with Guided Rule Editor

Change

Guided Rule Editor demo video

Demo video

Domain experts can read/write DSL even better

DSL is even easier to read/write

Developers create the building blocks

Domain experts make the building

Source: wikipedia

My business rules
change often

This mortgage rule change must be
released by noon

Deliver changes fast

Business rule change

Not a data changeRequires test and release lifecycle

Logic changes

Not a software changeDelivered in hours, not days

Self-service by mortgage manager

Testing before releasing

Domain experts need to unit test tooExample: mortgage of Erik (75) must be disapproved

Releasing

Release a snapshot of the rules package

Available at URL:http://127.0.0.1:8888/org.drools.guvnor.Guvnor/package/presentationmortgages/mortgagesDeployment

Deployment infrastructure

Auditable and reproducible

Why was that mortgage approved last year?

Auditing

View old revisions of rules

Future improvements

Feed-back welcome

Modules: reuse rules

Module contains assets (rules)Packages will be renamed to modules

Module can depend on other modulesReuse of assets (rules) from other modules

Dependency graph (like Maven/OSGi but simplified)

Mortgage rules

Car loan rules

General loan rules

Customer rules

2.0

1.1

1.1

2.1

Extended release lifecycle

Draft

Test

ReleasedVersion

Immutable (all dependent modules are released)

Summary

Summary

Use Drools and Guvnor

when your business decisions eitherRequire domain expertise

Change often/fast

Q & A

Questions?

Useful links

Website

http://www.jboss.org/drools/

Reference manual

http://www.jboss.org/drools/documentation.html

Blog

http://blog.athico.com/

Mailing lists (forum interface through nabble.com)

http://www.jboss.org/drools/lists.htmlSlides available online

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