Package Definition

Before defining the rules, it is necessary to build one or more containers capable of holding them.
These containers are Drools packages and they can be defined as follow:

PackageDefinition.java

public static void main(String[] args) {
  PackageDescr package = new PackageDescrBuilderImpl()
    .name("eu.trentorise.game.model")
    .getDescr();
}

In the above example we created a package whose name namespace is eu.trentorise.game.model.
Packages can be enriched with imports, globals, declarations and rules.

One rule per package

Even if this is not true for Drools, while using DSL4GaR each package should contain exactly one rule.

Imports

It is possible to import necessary classes inside a package as follow:

PackageDefinition.java - Imports

import eu.trentorise.game.model.BadgeCollectionConcept;

public static void main(String[] args) {
  PackageDescr package = new PackageDescrBuilderImpl()
    .name("eu.trentorise.game.model")
    .newImport(BadgeCollectionConcept.class)
    // Other imports...
    .getDescr();
}

All the imported classes can then be used inside the rule to apply the corresponding constraints.

Globals

Within a package it is also possible to define global variables in the following way:

PackageDefinition.java - Globals

import it.univaq.gamification.dsl.Global;

public static void main(String[] args) {
  final Global GLOBAL_VERONA_DISTANCE = new Global(Double.class, "verona_distance");

  PackageDescr package = new PackageDescrBuilderImpl()
    .name("eu.trentorise.game.model")
    // Imports...
    .newGlobal(GLOBAL_VERONA_DISTANCE).end()
    // Other globals...
    .getDescr();
}

In order to add a new global to a package it is necessary to declare a Global instance; its constructor accepts a Class that corresponds to the type of the global variable and a String that corresponds to the name of the variable itself.

Global reference

The Global object is not instantiated directly inside newGlobal method but its reference is kept in a variable GLOBAL_VERONA_DISTANCE so that it can be further referenced within the rule inside the package.

Types Declaration

A package can also hold type declarations:

PackageDefinition.java - Declarations

import it.univaq.gamification.dsl.Global;

public static void main(String[] args) {
  PackageDescr package = new PackageDescrBuilderImpl()
    .name("eu.trentorise.game.model")
    // Imports...
    // Globals...
    .newDeclare()
      .type().name(PRItinerary.class)
      .newField("length").type(Double.class).end()
      .newField("name").type(String.class).end()
    .end()
    // Other type declarations
    .getDescr();
}

In order to define a type, it is necessary to use the newDeclare method; it allows to define the class of the type to declare and its relative fields (with their corresponding types). In this case the following type has been declared:

rule.drl

declare PRItinerary
  length: Double
  name: String
end

tip

Inside a package it is possible to define imports, globals and types in any order!