Tutorials : A Closer Look at the Java Rules Engine API (JSR 94) :

Administrator API

The administrator API also uses the RuleServiceProvider Class to acquire an instance of the RuleAdministrator interface. The RuleAdministrator interface provides methods to register and de-register execution sets. The RuleAdministrator provides a remote and local RuleExecutionSetProvider. As mentioned before the RuleExecutionSetProvider is responsible for creating the RuleExecutionSets. The RuleExecutionSets can be created from a number of sources like XML streams, input streams etc. These sources and their contents can be marshaled and serialized across to a remote server where the rule engine is running. The scenario of a remote rule engine or remote sources could be rare in most applications. So to avoid the network overhead in these cases the API provides for a Local RuleExecutionSetProvider, which can read from sources running in the same JVM. The API does not mandate the local RuleExecutionSetProvider but vendors who do not implement the local RuleExecutionSetProvider will have to return null.

The RuleExecutionSet interface has methods to get the metadata about the RuleExecutionSet. It also has methods to retrieve all the rule objects defined within the RuleExecutionSet. This allows the client to know about the rule objects present in the RuleExecutionSet and use them as they need.

Security

The Rules engine API separates the administration and the runtime APIs so that fine grained security control can be provided for these packages. The Rules engine API does not provide any explicit security mechanism. The API is open enough to be plugged with the standard security API defined in the J2EE specification. Security can be provided with the Java authentication and authorization service (JAAS), the Java cryptography extension (JCE), Java secure Socket Extension (JSSE) or any custom made security API. JAAS can be used to define permissions to the RuleExecutionSets so that only authorized users are allowed to access them.

Exceptions and Logging

The Rules Engine API defines a javax.rules.RuleException as the root of the rules engine exception hierarchy. All other exceptions will extend from this root class. The exceptions defined in the rules engine are all checked exceptions, so the responsibility of catching the exception falls on the implementer.

The Rules Engine API does not provide an explicit logging mechanism, but it suggests that the Java Logging API be used with the Rules engine API.

Reference Implementation

In line with the recommendations of the Java Community Process, the Java rules Engine Specification provides a reference implementation. Unlike other reference implementations provided with other specifications, which are free, the Java Rule Engine reference implementation is not a full and free implementation. The rules engine specification uses the JESS rule engine and provides a wrapper around it. JESS is not freeware; so the license of the RI is governed under the JESS license agreement. However an academic license for JESS is offered at no cost. Information and licensing information about JESS can be found in the resources below.

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