2011-03-29 London - Why do I need the guvnor BRMS?

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
Because
Drools 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 decisions
Mortgages acceptance and interest calculation
Insurances acceptance and fee calculation
Price calculations
Phone/Telecom bills
Diagnostics
Possible diseases based on symptoms
Complex validation
Car parts selection
Not a good use case: an XML parser
Use Java code for that

Mortgages example

Developers don't like data input from spreadsheets
Before App 1.0: Mortgages rules in a spreadsheet
Which 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 code
Changing business rules not flexible enough
Business 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 repository
Flexible like spreadsheet
But fields clearly defined
No spreadsheet versions/copies
Auditable

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 have
university'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? No
Mortgage manager is the domain expert

Domain experts can not read/write Java source code
Communication problem
Domain 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 change
Requires test and release lifecycle
Logic changes
Not a software change
Delivered in hours, not days
Self-service by mortgage manager

Testing before releasing
Domain experts need to unit test too
Example: 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 modules
Reuse 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
Released
Version
Immutable (all dependent modules are released)

Summary

Summary
Use Drools and Guvnor
when your business decisions either
Require 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.html
Slides available online

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2011-03-29 London - Why do I need the guvnor BRMS?

by Geoffrey De Smet

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