Drools is split into two main parts: Authoring and Runtime.

The authoring process involves the creation of DRL or XML files for rules which are fed into a parser, defined by an Antlr 3 grammar. The parser checks for correctly formed grammar and produces an intermediate structure for the "descr"; where the "descr" indicates the AST that "describes" the rules. The AST is then passed to the Package Builder which produces Packages. Package Builder also undertakes any code generation and compilation that is necessary for the creation of the Package. A Package object is self contained and deployable, it is a serialized object consisting of one or more rules.

Figure 2.10. Authoring Components

A RuleBase is a runtime component which consists of one or more Packages. Packages can be added and removed from the RuleBase at any time. A RuleBase can instantiate one or more WorkingMemories at any time; a weak reference is maintained, unless configured otherwise. The Working Memory consists of a number of sub components, including Working Memory Event Support, Truth Maintenance System, Agenda and Agenda Event Support. Object insertion may result in the creation of one or more Activations. The Agenda is responsible for scheduling the execution of these Activations.

Figure 2.11. Runtime Components