Drools5 Community Training Sponsored by Plugtree

Module 1.5: Drools Expert First Example

Drools5 Community Trainingversion: 1.0-SNAPSHOT

Release Date: 03/16/2011Under The Creative Common License

Module 1.5: Drools Expert First Example

Drools5 Community Training Course by Mauricio "Salaboy" Salatino and Esteban Aliverti is licensed under a Creative Commons Attribution 3.0

Unported License.Based on a work at salaboy.wordpress.

com.Permissions beyond the scope of this

license may be available at http://salaboy.wordpress.com/.

Agenda

IntroductionBusiness Rule StructureDrools Expert Example ScenarioHands on lab

Drools Expert in 2 slides

The core of Drools Lets us express our Knowledge -> Business RulesLets us create Sessions -> Our World It will be in charge of making inferences between them and firing the correspondent actions.Let's see how it works!

Drools Expert in 2 slides

Business Rule Structure

rule "My Rule" when <LHS> Person(name == "John") <CEs> then <RHS> System.out.println("Hi John!"); <Actions>end

Example Scenario

Example Model

We can define that a Pet will have a name, type and a position.

For this example a Person will have a Pet which he/she can call. And this Person can also call the fire department. The Firefighter will know how to retrieve a Cat from a Tree.

Example Rules

Rule "Call Cat when it is in a tree" When my Cat is on a limb in a tree Then I will call my Cat

Rule "Call the fire department" When my Cat is on a limb and it doesn't come down when I call Then call the Fire Department Rule "Firefighter gets the cat down" When the Firefighter can reach the Cat Then the Firefighter retrieves the Cat

Technical View of  the Model

Technical View of  the Rules

rule "Call Cat when it is in a tree" when $p: Person($pet: pet, petCallCount == 0) $cat: Pet(this == $pet, position == "on a limb", type == PetType.CAT) then //$cat.getName() + " come down!" $p.setPetCallCount($p.getPetCallCount()+1); update($p); end

Rule "Call Cat when it is in a tree" When my Cat is on a limb in a tree Then I will call my Cat

Technical View of  the Rules

rule "Call the fire department" when $p: Person($pet: pet, petCallCount > 0) $cat: Pet(this == $pet, position == "on a limb", type == PetType.CAT) then Firefighter firefighter = new Firefighter("Fred"); insert(firefighter);end

Rule "Call the fire department" When my Cat is on a limb and it doesn't come down when I call Then call the Fire Department

Technical View of  the Rules

rule "Firefighter gets the cat down" when $f: Firefighter() $p: Person($pet: pet, petCallCount > 0) $cat: Pet(this == $pet, position == "on a limb", type == PetType.CAT) then $cat.setPosition("on the street"); retract($f); update($cat);end

Rule "Firefighter gets the cat down" When the Firefighter can reach the Cat Then the Firefighter retrieves the Cat

Active Scenario in Java

For the previous rules to fire in our Java world we need to have:An instance of a Person that contains a relation to its PetAn instance of a Pet that is on a limb

Person person = new Person("Salaboy!"); Pet pet = new Pet("mittens", "on a limb", Pet.PetType.CAT); person.setPet(pet);

API's Sneak Preview

Hands On

Project Name: drools5/00-Drools5-FirstExampleSources: https://github.com/Salaboy/Drools_jBPM5-Training-ExamplesCharacteristics:

Java Project (jar) Uses Maven (pom.xml)Drools Dependencies (core, api, compiler)DRL File (src/test/resources/rules.drl)

To do:Run the test (src/test/java/org/plugtree/example/FirstExampleTest.java)Get familiar with the output

Hands On

Exercise 1:Create a new rule that inserts a Dog (on the street) when there is Cat on the street too.Create a new rule for the situation when a Cat and a Dog are on the street, the Dog should chase it up to the tree and then the Cat should climb the limb.

Hands On - Solution

rule "Cat on the street" when Pet(position == "on the street", type == PetType.CAT) then Pet dog = new Pet("doggy", "on the street" , PetType.DOG); insert (dog);end rule "Cat on the street and a dog is around" when $cat: Pet(position == "on the street", type == PetType.CAT) $dog: Pet(position == "on the street", type == PetType.DOG) then modify($cat){ setPosition("on the limb"); } modify($dog){ setPosition("under the tree"); } end

Hands On - What Happen?

Exercise 1:What happens with the execution? Why?Try to find a solution

Briefing Up

Covered Topics:Quick review about Drools ExpertProject DependenciesA simple example that shows the key things that we need to have to use Drools

  

Questions?

Enjoy! Questions and Feedback are always appreciated!Stay Tuned!

  

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