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Drools Tutorial - Learn Drools from Scratch

Drools Tutorial - Learn Drools from Scratch


Drools is an open source project written in Java which is sustained by Red Hat, Inc and JBoss and is based on Business Logic integration Platform (BLiP). It is based on Rete Pattern matching algorithm and extends and implement the functionality of the algorithm. Drools is a collection of tools that permit us to isolate and purpose over data and logic initiate within business processes. 

There are 2 major components of drools: 

  • Authoring: This process comprises of the formation of Rules files which is .DRL files. 
  • Runtime: This process comprises of the formation of occupied memory and handling the initiation. 

Rule Engine:

A Production Rule Structure which is used by drools that practices the rule-based method to implement and Expert System. A Production Rule System is mainly focused on knowledge illustration to implement first-order and propositional logic in a brief, un-ambiguous and in explanatory manner.

Inference Engine is considered to be the brain of a Production Rules System that can measure to a large amount of facts and rules. It compares data and facts with Production Rules to conclude the action results. The Production Rule is a bipartite structure that customs first-order logic for reasoning over knowledge illustration. The business rule engine is a software structure that implements more than one business rules in a runtime production situation. A Rule Engine permits you to describe “What to Do” with the implementation but not describe “How to do it.”


Rules are considered as a fragments of knowledge articulated as, “When some conditions executes, then perform some tasks.” The most important part of a Rule is it’s when part. If the when part is fulfilled, the then part role comes into picture.

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Pattern Matching:

The procedure of comparing the new or old facts with the Production Rules which is completed by the Inference Engine is called pattern matching. There are a many algorithms used for Pattern Matching which also includes:

  • Rete Algorithm
  • Linear Algorithm
  • Leaps Algorithm
  • Treat Algorithm

The algorithm that is mainly used by Drools is the Rete Algorithm.

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Advantages of a Rule Engine:

  • Explanatory Programming

In drools, Rules make it simple to express explanations to challenging problems and get the resolutions tested as well. In comparison to codes, Rules are developed in less complex formats and Business Analysts can simply read and verify a group of rules. 

  • Separation of Logic and Data

The Domain Objects contains the data inside and the business logic contains the Rules. Depending on the nature of the project, this kind of separation can be very beneficial. 

  • Scalability and Speed

With the help of Drools, application becomes very accessible. In case of regular change requests, a provision for adding new rules is available without modifying the predefined rules. 

  • Knowledge Centralization

With the help of Rules, a warehouse of knowledge would be created which is executable in its form. 

  • Tool Incorporation

Various tools such as Eclipse offer means to manage and edit rules and get instant response, authentication, and content support. Inspecting and debugging tools are also accessible to get instant response about the inputs.

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