Drools Tutorial

In the context of businesses, there are many rules adopted precisely by the organizations to be followed. These business rules serve as an important element to look at the problems in a N number of ways.The business rules are very needy in representation of the business logics.The results outed from them are very interactive and intuitive , and help in decomposing the large issue into small parts for easy solving. With the advent of the drools tools, you can simplify your problem solving nature easily.To gain in depth knowledge or skills in using the drools rule engine logic, drools training course is very helpful. In this Drools Tutorial, I am going to share the concepts related to drools, rule, drools rule engine, drools tool suite, components, architecture of drools,key features, adding drools plugin,creating drools program, etc. Let's start exploring the concepts one after the other in detail.

1. What are drools?

DROOLS is an effective business rules management programme written in Java that utilizes an innovative rete pattern matching technique. It allows consumers with a range of features, such as Business Rule Engine, Online composing and Rules Management Framework, and full-time support for Decision Model and Notation Models. Drools has been released under Apache License 2.0 and is integrated with any JVM and is also accessible in Maven Central Repository.

The Drools platforms enable you to isolate and reason logic and data contained in enterprise applications. It facilitates forward and backward chaining inference-based drools rule engines. 

Drools are divided into two parts, namely: Authoring and Runtime. 

Authorisation-This includes the creation of the rules files. 

Runtime-This includes building a working memory and managing the activation.

2. What is the rule?

Rules are pieces of experience sometimes translated as When specific conditions occur, then do some tasks." 

The most critical part of the rule is when it comes to part. Once the part is fulfilled, the part is activated.

Syntax:

When

<Condition is true>

Then

<Take desired Action>

Pattern Matching method:

The Pattern Matching Method lets you equate old or new information with the rules of production. The Inference Engine is completed by the pattern matching method.. 

The algorithms used for pattern matching are as follows: 

  • Algorithm Rete 
  • Algorithm Leaps 
  • Linear Algorithm 
  • Treat the algorithm 

However the algorithm most widely used by Drools is the Rete Algorithm.

Rete Algorithm:

The Rete algorithm is a valuable pattern matching algorithm that helps you to enforce production rule systems. It makes you sacrifice your memory for pace. It also decreases or removes particular forms of redundancy with the aid of sharing the node. It stores partial matches while conducting junctions between various types of facts.

3. What is a rule engine?

The rule engine uses a rule-based approach to the application of an expert framework. Expert systems are information systems that enable you to make assessments. It collects information into an expert system that can be used for reasoning purposes.

4. Drools Tool Suite:

Here are five types of methods that are part of the Drools suite: 

  • Drools Guvnor: It is a centralised repository for Drools KnowledgeBase. 
  • Drools Flow provides workflow and business processes. 
  • Drools Fusion: a technique used to process complex events 
  • Drools Expert or Rules Engine: a valuable method for reasoning. 
  • Drools Planner: To deliver automatic planning, including NP-hard planning issues.
5. Components in Drools:

Here are the some of the components of the drools, they are:

  • Facts-The facts represent the data that is used as input for the rules 
  • Working Memory-Storage with Facts, where they are used to fit patterns. It can be changed, inserted and removed. 
  • Knowledge Session-This part holds all the resources needed for the fire law. Here all the details are put into the session, and then the matching laws are shot. 
  • Awareness Base-Represents knowledge in the Drools ecosystem. It stores the creation of resources where the rules are created.
  • Module-This is a module that stores various Knowledge Bases that can contain different sessions.

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6. Architecture of Drools:

Architecture of Drools

The functionalities of the rule engines are explained in the below steps. Look at them.

Step 1) The rules are placed into the Rule Base, which is always open. 

Step 2) Facts are reported in the Working Memory where they can then be changed or retracted. 

Step 3) The method of combining new or existing facts against the rules of production is called pattern matching, that is executed by the Rule engine. 

Step 4) The agenda helps you to control the order of execution of competing rules with the aid of a dispute resolution strategy.

Features of Drools:

The important features of the drools are :

  • Drools help you distinguish the programme from complex logic. 
  • It is a declarative programming; 
  • Centralisation of Knowledge 
  • It helps in achieving speed and scalability: 
  • It helps in separating logic of the application 
  • Easily understandable rules are derived from the drools.
Steps to add drools plugin into Eclipse:

Just follow the few steps to add the drools plugin into Eclipse. They are:

Go to the official website page and click the "Distribution ZIP" button for JBPM integration. Extract it from your hard drive after downloading as shown in the below image.

Steps to add drools plugin into Eclipse

Step2: In Eclipse, select install new software as shown in the below image.

install new software

Step3: Click on Add

Click on Add

step4:In the next screen, select the following:

Click on Local

Select folder "org.drools.updatesite/"

Click Ok

Click on Local

Step5: Click next button as shown below:

Click next button as shown below

Step6: Accept the terms and conditions and click next.

Accept the terms and conditions and click next

Step7: Software will be downloaded and you will be asked to reboot the eclipse

Step8: In Windows > Preferences menu, you will see the Drools option that means that it is installed.

Drools option that means that it is installed

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9. Creating the drools program:

package com.sample

import com.sample.DroolsTest.Message;

rule "Hello World"

 when

m : Message( status ** Message.Hello, myMessage : message )

  then

System.out.println( myMessage );

m.setMessage( "Goodbye cruel world" );

m.setStatus( Message.GOODBYE ); 

update( m );

end

 rule "GoodBye"

when

Message( status ** Message.GOODBYE, myMessage : message )

then

System.out.println( myMessage );

end 

10: Backward and forward chaining

A forward-track engine reviews the details and draws a clear inference. 

Consider the situation of a medical diagnostic method. If the symptoms of the patient are put into the working memory as evidence, it is easy to diagnose the disease.

Backward and forward chaining

The backward chaining engine has a fixed target, and the engine is trying to satisfy it. 

Consider the same medical diagnosis situation. Suppose there is an outbreak of a certain disease. This AI should have concluded that the person had a disease and tried to assess if the diagnosis was right on the basis of available knowledge.

backward chaining engine

11. Why use drools rule engine?

  • Rules are easy for developers and market analysts to grasp. 
  • Rules are quickly preserved. 
  • Rule Engine uses a Rete algorithm which states that the output of the engine is never dependent on the number of rules. 
  • Laws may be modified and implemented without the request being made. 
  • Extends business logic from a comparatively static codebase. 
  • Rules are formulated in less complex formats such that a group of rules can be easily read and checked by a business analyst.
  • The rules allow you to create an information warehouse that is executable in a form. 
  • Tools like Eclipse help you manage rules, get instant response, authentication, and support for content
12. Drawbacks of drools rule engine:

The drawbacks of drools rule engine are:

  • A variety of learning efforts needs developers to understand this programming process. 
  • Rule engine is not a safe tool for troubleshooting issues. 
  • Needs to understand how the rule engine operates to use more memory 
  • There is a broad collection of rules for complex branching.

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Conclusion:

Drools is a solution for the Business Rule Management System (BRMS). It offers a rule engine that handles facts and generates output as a result of the processing of rules and facts. Centralization of business processes makes it possible to make improvements rapidly and cheaply. 

It also fills the gap between company and domain experts by offering an easy-to-understand set of guidelines for writing.

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Kavya Gowda
Kavya Gowda
Research Analyst
Kavya works for HKR Trainings institute as a technical writer with diverse experience in many kinds of technology-related content development. She holds a graduate education in the Computer science and Engineering stream. She has cultivated strong technical skills from reading tech blogs and also doing a lot of research related to content. She manages to write great content in many fields like Programming & Frameworks, Enterprise Integration, Web Development, SAP, and Business Process Management (BPM). Connect her on LinkedIn and Twitter.