What is Drools?

Drools is one of the Business Rule Management Systems (BRMS) that helps find simple solutions to complex problems. It is a tool with robust AI capabilities to deal with business rules and data. The rule engine is the core of Drools, which chooses the best business rule against the input data and execute the rules to derive better results. Do you want to know more about Drools? No more wait! This blog will closely walk you through the various features of Drools.

Undeniably, change is the only constant. No single entity in the world can be exempt from this law of nature. On that note, when it comes to specific complex business processes, they will change constantly. Subsequently, you must change the code of their software applications as well.

In traditional software systems, you cannot change the codes every time there is a change. It is a tedious and time-consuming task. But, at the same time, you must adapt to the changes as soon as possible. You can solve this problem by changing the business rules instead of changing codes all the time. Business rules are derived from business logic. Simply put, Business Rule Management System (BRMS) is the right solution.

This way, Drools is one of the BRMS tools that helps overcome this setback and simplify business management. Know that Drools is part of the KIE community. KIE refers to ‘Knowledge in Everything’. KIE provides the best solutions for business automation as well as management. OptaPlanner, Kogito, and JBPM are some other KIE solutions.

In this blog, you will go through the basics of Drools, its architecture, features, and many more at a closer look. Let’s go ahead!

Drools Tutorial - Table of Contents

What is Drools?

Drools is one of the widely used Business Rule Management Systems (BRMS). It is an open-source tool written in Java. So, you can run Drools in any JVM. You can get this tool in Maven central repository. With Drools, we can build and run business rules. The rules help to make better decisions with the help of the AI-based automation capabilities of Drools. Thus, we can simplify complex business processes.

Drools comes with many crucial components, such as:

  • Business Rule Engine (BRE)
  • A Drools Workbench
  • An IDE plugin.

The first component, the rule engine, is nothing but a forward as well as backward chaining rule-based engine. Know that forward-chaining rule engines derive conclusions from the given facts or inputs. On the other hand, the backward chaining rule engine checks whether the given facts satisfy a goal.

Another one, Drools Workbench or JBoss rules Workbench, is nothing but an Integrated Development Environment. This is where you can create and test codes. Additionally, Drools does two crucial functions – authoring as well as runtime. Here, authoring refers to creating business rules. In another part, runtime refers to creating working memory as well as triggering the rule engine.

Drools is an expert system where the rule engine is one of the building blocks. Typically, expert systems are knowledge-based systems with which you can make accurate decisions. This is just because they accumulate knowledge in the knowledge base that helps to simplify decision-making.

If you want to enrich your career and become a professional in Drools, then enroll in "Drools Online Training". This course will help you to achieve excellence in this domain.

The Architecture of Drools

Drools architecture comprises various elements such as a rule base, rule engine, working memory, production memory, and agenda.

Drools Architecture

1. Rule-Engine

A rule engine is also an inference engine that works based on AI capabilities. No wonder it acts as the brain of Drools.

Know that the rule engine uses a pattern-matching method. This method works based on the Rete algorithm. In this method, the rule engine compares the incoming data or facts with business rules based on the ‘if-then’ rule and finds the matching rules. And then, the rule engine executes the matching rule to derive better decisions.

It is essential to note that the pattern-matching method helps increase execution speed.

2. Rules

Essentially, Drools follow a rule-based approach. Business logic is expressed as rules. In its basic form, rules are declarative and expressed in human-readable form. Rules are usually stored in a rule base.

The business rules are framed in the ‘If-then’ structure. It means that they have conditions along with the associated actions.

The syntax for writing a rule is given as follows:

Rules Syntax

3. Facts

It is the incoming data that the rule engine receives. With facts, we can perform pattern matching. Also, we can store facts in the working memory. We can add, modify, and delete facts by executing rules in the rule engine. Not only that but facts can also be modified because of external sources.

4. Production Memory

This is the place where business rules are stored. This memory is never disturbed during the analysis session. You cannot add or delete any rule in the production memory during the analysis session. At the same time, once the session is over, you can add or remove rules in the production memory.

5. Working Memory

As you know, this is where the facts are stored. You can add, modify, and remove facts in working memory. Unlike production memory, you can change the contents of this memory during the analysis session.

A simple but essential note is that you must store facts relevant to the business logic. Then only it will increase the performance of the rule engine.

6. Agenda

It is the place where applicable business rules are registered and prioritized. It allows the rule engine to execute the business rules in the correct order in the following stage. Besides, the agenda uses the conflict resolution strategy to manage the conflicting rules smoothly.

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Why Drools?

Of course! Drools is one of the best tools for business Rule management systems. Let’s take a close at the reasons to consider:

  • When the business is too complex or constantly changing, then Drools will be highly useful for making in-depth business solutions
  • The main thing about Drools is that it decouples business logic from the application code as well as data
  • Drools helps to reduce the gap between business analysts and developers simply because analysts can quickly understand business logic more than codes.
  • It centralizes knowledge by creating a centralized knowledge repository. As a result, it empowers applications to run to their maximum efficiency.
  • Drools allows maintaining business rules effortlessly.

How Does the Drools Rule Engine Work?

As you know, Drools separates business logic from the application as well as facts. Business logic is usually defined by business rules. So, if you want to change the business logic, you can change the associated business rules rather than changing codes.

Working of Drools Rule Engine

Drools' rule engine works based on the Rete algorithm. In general, facts are the inputs to the rule engine. And the output can be modified facts or new facts. When there is any change in the working memory of Drools, it will trigger the rule engine. The engine matches the facts with the rule base and identifies the matching rule. After that, the matching rule is executed by the rule engine.

Suppose there are multiple rules selected, and the order of execution of rules is managed by agenda. In other words, the agenda prioritizes the execution rules based on the conflict resolution strategy. So, the engine continues executing rules until the agenda gets empty. Once this process is over, you can get the results from the working memory. You can undoubtedly get high-level decisions from low-level facts with the help of Drools' rule engine.

What is Drools Suite?

Let’s look at the different elements of the drool suite in the following:

  • Drools Expert: It is the rule base engine used for reasoning.
  • Drools Fusion: It is an integrated engine extension with which you can manage complex event processing.
  • Drools Planning: It optimizes the distribution of resources and their usage through automated resource planning. Even you can solve NP-hard planning with the help of the Drools rule engine. Mainly, Drools considers multiple solutions for problems and chooses the right one.
  • Drools Flow: It includes workflows as well as business processes.
  • Drools Guvnor: It is the centralized repository that acts as the Drools knowledge base. This is where you can store rules, models, processes, and other associated things. Besides, it has a layer of authentication to secure the data in the repository.
  • Drools Workbench: It is a web User Interface used to author as well as manage business rules.

Features of Drools

Drools offers excellent features to streamline business rule management systems. Want to know them in detail? Let’s have a read ahead!

1. Business Rules

Drools follows declarative programming. In a way, it helps to find better solutions for complex problems. You can define your business logic through business rules. No wonder business rules are close to natural language. It means that they are human-readable. Therefore, business analysts can quickly understand business rules and work efficiently.

2. Isolation

In Drools, business rules and application codes are isolated altogether. Not just codes, data is also separated from the business rules. In other words, Drools use production memory to store business rules and working memory to store facts. So, changes that you make in business logic won’t affect application codes in any way.

3. Rete Algorithm

Basically, this algorithm includes two essential elements – rule compilation as well as runtime execution. This algorithm matches business rules with facts to find the best matching rules. It analyses facts as much as possible to increase efficiency. No wonder this algorithm can sense even small changes in the facts and process them further.

4. Integration

As you know, knowledge is centralized in Drools. This knowledge base acts as the single point of truth. By using Git tools, you can integrate the Drools engine with the rules repository. Additionally, Drools engine integrates with eclipse IDE, which supports editing and managing business rules. Not only that, you can get validation, feedback, and other quick support with this IDE.

5. Visibility

Drools allows viewing the current state of the analysis session. Also, you can analyze the data stored in the working memory and the rules stored in the production memory. The rule engine stores the results in the working memory once choosing the best matching rules and executing them. Besides, it stores the reasons for choosing the rules.

Applications of Drools

Let’s see a few noteworthy applications of Drools in the following. With Drools, you can:

  • Validate timesheets of employees and make payrolls.
  • Simplify claim settlements of employees for insurance and others.
  • Manage the sales pipeline from the first contact to the sale's closing.
Learn Top Drools Interview Questions and Answers that help you grab high-paying jobs

Advantages and Disadvantages of Drools

Every coin has two sides. On that note, we must understand that drools has both pros and cons.

Let’s uncover them below one by one.


  • Drools follows a rule-based approach, which solves complex problems with simple solutions.
  • You can store rules in one place, usually in repositories.
  • Rete algorithm doesn’t depend on the number of rules. So, the addition of new rules doesn’t affect the performance of systems. Instead, the performance is improved since it opens up new possibilities.
  • Drools provides greater flexibility and speed.
  • Maintainability is good in Drools since it is easy to change business logic rather than changing codes.
  • Drools offer good scalability. So, you can add or modify or delete rules as much as possible.


  • When business logic is simple, there is no point in using Drools
  • If you cannot split the business systems into small parts, then Drools won’t be a suitable solution
  • It is possible that a large volume of rules makes complex branching in the rule base.


On a final note, Drools separates business logic from facts and application codes. As a result, it supports finding better solutions for complex problems with its AI capabilities. Business rules are similar to natural language, which helps to understand the rules quickly. So, it reduces the gap between developers and business analysts. As a whole, Drools offers good flexibility, maintainability, scalability, and much more. So, if you want to find a suitable solution for your complex problem, Drools is undoubtedly one of the go-to tools.

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Last updated: 04 Apr 2023
About Author


Madhuri is a Senior Content Creator at MindMajix. She has written about a range of different topics on various technologies, which include, Splunk, Tensorflow, Selenium, and CEH. She spends most of her time researching on technology, and startups. Connect with her via LinkedIn and Twitter .

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