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Drools5 Community Training Sponsored by Plugtree

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Module 3: Drools Expert DRL Syntax Drools5 Community Training version: 1.0-SNAPSHOT Release Date: 03/16/2011Under The Creative Common License

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Module 3: Drools Expert DRL Syntax 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/.

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Agenda● Introduction to Drools Expert● Drools DRL syntax introduction ○ LHS Conditional Elements ○ RHS ○ Rules attributes ○ Queries● Drools 5.x APIs introduction

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Drools Expert Introduction● Drools Expert is the rule engine core● Lets us express Business Rules● It will be in charge of making inferences to get new conclusions

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Components interaction

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Rules Execution Cycle

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Business Rule Structurepackage ...import ...global ...rule "My Rule" <Attributes> when <LHS> Song(genre == "Jazz") <CEs> then <RHS> System.out.println("Hi John!");end

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LHS - Conditional Elements● Pattern● e.g.Song(genre == "Jazz")$song: Song(genre == "Jazz" || == "Avantgarde")$song: Song(duration > 360, $genre: genre == "Jazz")

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LHS - Conditional Elements● Field Operators● e.g.Song( lyrics matches "AZ-az[drink]" )Song( authors contains "John Zorn" )Song( author memberof $greatMusicians )

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LHS - Conditional Elements● AND e.g. Person( name == "John" ) AND Pet(type == "cat")● OR e.g. Policewoman (age > 30) OR Fireman(age > 31)

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LHS - Conditional Elements● eval e.g. eval( song.isJazz() )● not e.g. not( Song( genre == "Pop") )

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LHS - Conditional Elements● exists e.g. exists ( Song(genre == "Jazz"))● forall e.g. forall ( Song() Song(genre == "Jazz") )

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LHS - Conditional Elementsfrom CE ● e.g. $playlist: Playlist() Song() from $playlist.songs $playlist: Playlist() Song(genre == "Jazz") from $playlist.songs

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LHS - Conditional Elements● from● e.g. global HibernateSession hbn; $playlist: Playlist() Song() from hbn.namedQuery("SongByArtist") .setParameter("artist","John Zorn") .getResultList();

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LHS - Conditional Elements● Collect● e.g. $songs: ArrayList() from collect (Song(genre == "Jazz", year > 2000))

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LHS - Conditional Elements● Accumulate

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LHS - Conditional Elements ● Accumulate CE:<result pattern> from accumulate( <source pattern>, init( <init code> ), action( <action code> ), reverse( <reverse code> ), result( <result expression>)) ● e.g. $playlist: Playlist() $jazzSongs: Number( doubleValue > 100 ) from accumulate( Song(playlist == $playlist, genre == "Jazz"), init( double total = 0; ), action( total += 1; ), reverse( total -= 1; ), result( total ))

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LHS - Conditional Elements ● Accumulate Function Examples $playlist: Playlist() $total: Number( doubleValue > 100 )from accumulate( $song: Song( playlist == $playlist, genre == "Jazz"), count($song))

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LHS - Conditional Elements● Accumulate out-of-the-box Functions ○ average ○ min ○ max ○ count ○ sum

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LHS - Conditional Elements● Accumulate custom function$playlist: Playlist() $total: Number( doubleValue > 100 ) from accumulate( $song: Song( playlist == $playlist), myCustomFc($song.duration))● We can plug our custom function here. We just need to implement the AccumulateFunction interface.

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Nesting CEs● Drools support nested CEs $petshop: PetShop() $total: Number( doubleValue > 10 ) from accumulate( $pet: Pet(petshop == $petshop, type == PetType.Cat) from $hbm.getNamedQuery("getPetsFromPetshopId") .setParamenter("petshopid",$petshop.getId()) .list(), count ($pet) )

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Right Hand Side● Set of actions● MVEL or Java (http://mvel.codehaus.org/)● We will have a set of methods to modify the working memory status ○ insert() ○ modify() / update () ○ retract() rule "Fire ! ! !" when Fire() then insert(new Alarm()); end

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Rule Attributes

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Rule Attributes - no loop● no-loopi.e. rule "infinite activation loop" no-loop true when $person: Person(age > 21) then update($person){ setName("John"); } end

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Rule Attributes - salience ● salience (higher priority first)rule "rule with priority" salience 10 when $song: Song() then System.out.println("Rule with higher priority Fired!");endrule "rule with less priority" salience 5 when $song: Song() then System.out.println("Rule with lower priority Fired!");end

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Rule Attributes - agenda-group rule "Playlist ready" agenda-group "Create Playlist" when Playlist(size == 3) then //Set the focus to "Play playlist" agenda-group kcontext.getKnowledgeRuntime().getAgenda() .getAgendaGroup("Play playlist").setFocus(); end rule "Play playlist" agenda-group "Play playlist" when $pl : Playlist() then $pl.play(); end

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Rule Attributes - lock-on-activerule "Fill playlist" rule "Number Songs" salience 1 salience 2 lock-on-active lock-on-active agenda-group "Create Playlist" agenda-group "Create Playlist" when when $pl : Playlist() $song : Song() $song : Song() then then modify($song){ modify($pl){ setName( addSong($song); index.getAndIncrement()+ } "_"+ $song.getName());end } end

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QueriesExample query "Get Persons by Name" (String name) Person(name = :name)end

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Drools Expert APIs

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KnowledgeBuilder KnowledgeBuilder kbuilder = KnowledgeBuilderFactory.newKnowledgeBuilder();// Add our ruleskbuilder.add(new ClassPathResource("rules.drl"), ResourceType.DRL);//Check for errors during the compilation of the rulesKnowledgeBuilderErrors errors = kbuilder.getErrors();if (errors.size() > 0) { for (KnowledgeBuilderError error : errors) { System.err.println(error); } throw new IllegalArgumentException("Could not parse knowledge."); }

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KnowledgeBase // Create the Knowledge Base KnowledgeBase kbase = KnowledgeBaseFactory.newKnowledgeBase(); // Add the binary packages (compiled rules) to the KnowledgeBase kbase.addKnowledgePackages(kbuilder.getKnowledgePackages());

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KnowledgeSession // Create a StatefulSession using the KnowledgeBase that // contains the compiled knowledgeStatefulKnowledgeSession ksession = kbase.newStatefulKnowledgeSession();// We can add a runtime logger to understand what is going on// inside the EngineKnowledgeRuntimeLoggerFactory.newConsoleLogger(ksession);// Insert a new Fact inside my worldFactHandle myFactHandle = ksession.insert(new Person("Myself"));// Update a Fact using the FactHandleksession.update(myFactHandle, new Person("Salaboy!"));// Retract/Remove from my world the Factksession.retract(myFactHandle);

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Full Picture

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Hands on LabsProjects: ● 01 :: Drools Expert Introduction ● 02 :: Drools Expert Conditional Elements ● 03 :: Drools Expert Rule Attributes

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Briefing Up● Covered Topics: ○ Rules Execution Lifecycle ○ DRL Syntax ■ Conditional Elements in the LHS ■ Actions in the RHS

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Questions?

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Enjoy! Questions and Feedback are alwaysappreciated!Stay Tuned!

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