Writing rules

You write rules to define the business logic of the agent. A rule agent encapsulates the business logic that updates the state of its bound entity.

About this task

The rules define the action to be taken when an agent receives an event. An agent can listen to several events, but is always associated with a bound entity. The binding to the entity is defined at the agent level. The rule references the entity through the authoring context.

Through rules, rule agents can emit new events, and also create and destroy the bound entity.

Structure of rules
A rule defines the specific actions to take when certain conditions are met. A rule is composed of several parts that define the conditions and actions. The structure of the rule depends on the type of rule that you want to write.
Variables available in rules
Several types of variables are available when you write rules. Variables include the bound entity and the events that are defined in the agent descriptor, variables in the definitions part of the rule, and variables that are defined at the agent project level.
Inserting terms and phrases in the rule editor
You write rules using a near-natural language based on the vocabulary from the elements defined in the business model. The editor helps you to write the rules by providing an automatic completion mechanism to select the constructs and statements that make up the rule.
Adding a when part
A rule agent can process a specific event immediately upon its arrival into the system, or after a delay.
Adding a definitions part
You add a definitions part in a rule to create variables that can be used within the rule, and to simplify certain expressions.
Adding an if part
You use the if part to state under which conditions to carry out the rule actions that are defined in the then and else parts.
Adding a then and an else part
Rule actions define what to do when the if part of the rule is true or false. You define actions in the then and else parts of a rule.
Creating, updating, and deleting the bound entity
An agent can manage the lifecycle of its bound entity by writing rules that create, update, and delete the entity.
Getting values from global aggregates in rules
Use the values of global entity aggregates and global event aggregates in your rules to evaluate conditions and make decisions.
Getting values from shared aggregates in rules
Use the values of shared aggregates in your rules to evaluate conditions and make decisions.
Operating over past events
You can write rules that run tests on several events of the same type. For example, you can test that several event instances happened over a certain period.
Emitting an event
You can emit an event from a rule agent. In the action part of a rule, you use the emit <an event> keyword to create an event that is sent out when the agent is triggered, if the conditions apply. The emitted event can then be processed by the agents that listen for this event type.
Scheduling the execution of a rule
You can define when a rule must be executed by writing a temporal condition that uses the time now.
Reasoning over time and events
Write rules that contain time-aware business logic to reason over events and other time elements such as periods, durations, and current time.
Reasoning over geographic locations
Write location-aware rules to reason over geographic data of entities and events.
Null values handling in rules
Null values in rule conditions can prevent some rules from being fired. You can add tests in your rules to identify null values.