Drools

Drools is a business rule management system (BRMS) and an enhanced Rules Engine implementation, ReteOO, based on Charles Forgy's Rete algorithm tailored for the Java language.

More importantly, Drools provides for Declarative Programming and is flexible enough to match the semantics of your problem domain with Domain Specific Languages, graphical editing tools, web based tools and developer productivity tools.

FeaturesEngine
- Full Rete Implementation -- with high performance indexing
- Dynamic RuleBases
- Stateful and Stateless Execution Modes
- Async operations
- Rete and Sequential Rete
- Rule Agent
- Optional Data Shadowing
- Pluggeable Dialects
Propositional Logic
- Literal Restriction
- Variable Restriction
- Return Value Restriction
- Jointed and dis-jointed Connectives allowed - '&&' '||'
- inline-Eval
First Order Logic (Quantifiers)
- And
- Or
- Exists
- Not
- Accumulate
- Collect
- From
- Forall
- Nesting of any CE inside of 'and' and 'or'
- Support for both infix and prefix 'and'/'or' CEs
- Nesting and Chaining of 'from', 'accumulate', 'collect'
Execution Control
- Conflict Resolution (salience) Now pluggeable
- Agenda Filters
- Agenda Groups
- Activation Groups
- Rule Flow
- Attributes (no-loop, lock-on-active)
Temporal Rules
- Scheduler for rule duration will fire when a rule is true for X duration
Truth maintenance with Logical Insertions

Event Model
- Working Memory, Agenda and Rule Flow
Configurable
- All Rete optimizations and execution behavior can be configured
Authoring
- Technical rules: DRL and XML formats supported
- Template based DSLs
- Guided Editor
- BRMS and Eclipse
- Decision Tables (Excel, Open Office)
BRMS (Knowledge Asset Management System)
- Authoring and Storage DRLs, RuleFlows, Decision Tables, Business Rules (Guided Editor)
- Multi level Versioning, at both the rule and package level
- Classification
- Deployment
- Built on Standards and Open APIs - JCR (JSR 170) Dublin Core, GWT