2.5.3. RuleBase
Figure 2.16. RuleBaseFactory
A RuleBase is instantiated using the RuleBaseFactory, by default this returns a ReteOO RuleBase. Packages are added, in turn, using the addPackage method. You may specify packages of any namespace and multiple packages of the same namespace may be added.
RuleBase ruleBase = RuleBaseFactory.newRuleBase(); ruleBase.addPackage( pkg );
Example 2.7. Adding a Package to a new RuleBase
Figure 2.17. RuleBase
A RuleBase contains one or more more packages of rules, ready to be used, i.e., they have been validated/compiled etc. A Rule Base is serializable so it can be deployed to JNDI or other such services. Typically, a rulebase would be generated and cached on first use; to save on the continually re-generation of the Rule Base; which is expensive.
A Rule Base instance is thread safe, in the sense that you can have the one instance shared across threads in your application, which may be a web application, for instance. The most common operation on a rulebase is to create a new rule session; either stateful or stateless.
The Rule Base also holds references to any stateful session that it has spawned, so that if rules are changing (or being added/removed etc. for long running sessions), they can be updated with the latest rules (without necessarily having to restart the session). You can specify not to maintain a reference, but only do so if you know the Rule Base will not be updated. References are not stored for stateless sessions.
ruleBase.newStatefulSession(); // maintains a reference. ruleBase.newStatefulSession( false ); // do not maintain a reference
Packages can be added and removed at any time and all changes will be propagated to the existing stateful sessions. Do not forget to call fireAllRules() for resulting Activations to fire.
ruleBase.addPackage( pkg ); // Add a package instance ruleBase.removePackage( "org.com.sample" ); // remove a package, and all its parts, by it's namespace ruleBase.removeRule( "org.com.sample", "my rule" ); // remove a specific rule from a namespace
While there is a method to remove an individual rule, there is no method to add an individual rule. You just add a new package with a single rule in it.
RuleBaseConfigurator can be used to specify additional behavior of the RuleBase. RuleBaseConfiguration is set to immutable after it has been added to a Rule Base. Nearly all the engine optimizations can be turned on and off from here, and also the execution behavior can be set. Users will generally be concerned with insertion behavior (identity or equality) and cross product behavior(remove or keep identity equals cross products).
RuleBaseConfiguration conf = new RuleBaseConfiguration();
conf.setAssertBehaviour( AssertBehaviour.IDENTITY );
conf.setRemoveIdentities( true );
RuleBase ruleBase = RuleBaseFactory.newRuleBase( conf );
