The Imixs Rule Engine

The Imixs Workflow project provides a powerful, fast and very flexible rule engine based on the GraalVM. Rules can be written in different popular languages and can be combined with additional features and libraries.

The Imixs Rule Engine integrates seamless into the Imixs Workflow engine and comes in two different versions to evaluate business rules:

  • BPMN RuleEngine - used to evaluate a business rule based on a BPMN 2.0 workflow model.
  • Core RuleEngine - used to evaluate a business rule during the processing life cycle of a process instance.

The BPMN Rule Engine

The Imixs BPMN Rule Engine automatically evaluates a business Rule based on a standard BPMN 2.0 model. These kind of business rules are based on conditional events. Each condition has full access to the workitem and event object being processed.

A condition in a BPMN business rule is evaluated to a boolean indicating if the condition is true or false:

(workitem.getItemValueDouble('budget') > 100) && ('finance'.equals(workitem.getItemValueString('category'))

See the section conditional events to learn how you can model business rules.

Calling the BPMN Rule Engine Programmatically

As an alternative to conditional events the Imixs BPMN Rule Engine can also be called programmatically from your Java code. For this purpose the Rule Engine is initalized with an existing Imixs BPMN Model instance. To evaluate the rules a workitem containing the business values can be applied by the eval() method:

bpmnRuleEngine=new BPMNRuleEngine(model);

workitem = new ItemCollection().model(MODEL_VERSION).task(100).event(10);
workitem.setItemValue("a", 1);
workitem.setItemValue("b", "DE");

// evaluate rule
Assert.assertEquals(200, bpmnRuleEngine.eval(workitem));

The BPMN RuleEngine is based on the Imixs Core Rule Engine which is explained in the next section.

The Core RuleEngine

The Imixs Core RuleEngine evaluates any kind of business rules based on the build-in GraalVM script engine. A business rule can be written in any script language supported by the GraalVM. The RuleEngine can be used in a BPMN event to evaluate business rules based on the Imixs RulePlugin.

The Imixs Core RuleEngine provides direct access to the item values from a given current workItem or BPMN event. The results of a business rules are stored in an object named result which is mandatory.

// test the value of the workitem attribute 'name'
var result={}; result.isValid = ('Anna'==workitem.getItemValueString('name'));

A business rule can add additional values to the JSON based result object:

 var result={ someitem:'Hello World', somenumber:1};

These additional items will be stored in the current process instance. See the section Imixs RulePlugin for further details.

Calling the Core Rule Engine Programmatically

You can call the Imixs Core RuleEngine programmatically from your java code. The method evaluateBusinessRule() expects a script containing the business rule and the optional objects workitem and event to be evaluated in the script. See the following example:

ruleEngine = new RuleEngine();
ItemCollection workitem = new ItemCollection();
workitem.setItemValue("name", "Anna");
// define a script
String js = "var result={}; if ('Anna' == workitem.getItemValueString('name')) result.colleague='Melman';";
// evaluate the business rule
workitem = ruleEngine.evaluateBusinessRule(js, workitem, null);
Assert.assertEquals("Melman", workitem.getItemValueString("colleague"));


The method evaluateBusinessRule evaluates the business rule. The method returns the instance of the evaluated result object which can be used to continue evaluation. If a rule evaluation was not successful, the method returns null.

workitem = ruleEngine.evaluateBusinessRule(js, workitem, event);


The method evaluateBooleanExpression can be used to evaluate a boolean expression. The method takes a workitem as an optional argument and returns a boolean value indicating the result of the business rule.

ItemCollection workitem = new ItemCollection();
workitem.setItemValue("budget", 1000);
boolean result = ruleEngine.evaluateBooleanExpression("(workitem.getItemValueDouble('budget')>100)", workitem);

All kind of boolean business rules are mainly used to evaluate conditional events.