Drools Interview Questions

Drool is a business rule management system consists of backward and forward interfaces. If you are looking for the top 15 Drool interview questions and answers, then you are at the right place to learn and explore the important concepts of the Drool tool. As per the latest research, more than 1.78% of the market depends on the drool tool. Are you ready to upgrade drool skills? Then here you go, HKR’s recently designed drool interview questions and answers will help you to crack any complex interview. What you are waiting for, let’s begin the journey;

1. What is a Drool tool?

Ans: Drool is nothing but a business rule management system (BRMS) tool, which is provided by the JBoss community. This type of tool is designed to implement complex applications based on automatic behavior and rules. Drool is also known as the framework, this framework is developed on the base of the algorithm called rete pattern-matching algorithms. Drool is written using java and it’s an open-source project tool used by JBoss and Red Hat. The two main keywords here we use are Logic and data.

2. What are the main parts of Drool tools?

Ans: The following are the two important parts of the Drool tool such as;

1. Authoring -> this process is used to generate Rules files or DRL files.

2. Runtime -> this process is used to create working memory and handling all types of activations.

3. What do you mean by Rule in Drool?

Ans: A rule is a piece of knowledge that is used to perform specific tasks based on the conditions.

The syntax is as follows;


 < Condition is true>


 < Take desired action>









4. What are the important components of the enterprise version?

Ans: Below are the important components of the enterprise version;

1. JBoss enterprise web platform-> this contains software infrastructures and BRMS components.

2. JBoss enterprise application platform or JBoss enterprise SOA platform-> this consists of software infrastructures, and run only BRMS components.

3. Business rules manager-> this consists of drools guvnor and GUI editors.

4. Business Rules repository -> this consists of Drools Guvnor.

Below are the components of the JBoss community version:

1. Drools Guvnor or Business rule manager

2. Drools expert or rule engine.

3. Drools flow or process/workflow

4. Drools fusion or event processing /temporal reasoning.

5. Drools planner or Optaplanner.

5. What do you mean by pattern matching?

Ans: Pattern matching is a process of matching any new or existing facts which can be done against production rules. The complete pattern matching is performed by the Inference Engine.

There are many algorithms used to perform pattern matching;

1. Linear

2. Treat

3. Rete

4. Leaps.

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6. What are Drool workbench, Expert, and Fusion?

Ans: Drool workbench uses the web user interface to perform authoring and management tasks.

Drool expert is also known as a business rule engine.

Drool fusion is the feature used to process complex events.

7. What is a Knowledge session in Drool?

Ans: The knowledge session in Drool nothing but a session retrieved from the knowledge base. This is also known as the main interface for the drool engine.

There are two types of knowledge session available such as;

1. Stateless knowledge session

2. Stateful knowledge session.

8. What is the global variable and nomenclature in Drool?

Ans: The global variables are the keywords used in Drool. This global variable is a variable and which are visible to all the rules available in the DRL file.

Nomenclature is also known as a production rule system that uses the enhanced Rete algorithm implementations.

9. What are the key features of the JBoss Enterprise Application Platform?

Ans: Some of the important key features of the Jboss enterprise application platform;

1. Eclipse based IDEs are available using the Jboss developer studio.

2. Java persistence uses hibernate.

3. Supports the Java EE and web service standard tools.

4. Object request broker in Drool uses the JACOBS which is interoperability with any CORBA objects.

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10. What do you understand by Drools stateful vs stateless knowledge session?

Ans: Let me explain one by one;

1. Stateless session:

a. Any changes which are made while executing the rules will not affect the rule engine.

b. dispose() method in drool is called automatically mainly used to release the session.

c. Any changes made in the executing rules will not affect the rule engine, this means that any rule is modified no other re-activation rule engines will take place.

2. Stateful session:

a. Any changes which are made while executing the rules will affect the rule engine.

b. Dispose  () method in drool is called to release the session to avoid any memory leaks.

c. Any changes made in the executing rule will affect the rule engine for a particular fact; you can also reactivate all the drools rules and also modify them.

11. Which drools attribute have you used?

Ans: Below are the important drools attributes which we are using;

1. Salience -> salience in drool is used to figure out which drool tool we have to fire first.

2. No loop -> with the help of this attribute, you can avoid an indefinite looping system.

3. Update statement -> this attribute updates the statement and also modifies the rule facts.

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12. List the different execution control statements used in the drool tool?

Ans: Some of the different execution control statements used in drool tool such as;

1. Agenda group: this is an optional keyword in Drool. If any type of rule is not assigned to any group, it will belong to the main agenda by default.

2. Activation group: this is a reserved keyword available in drl file. Here either singular or multiple rules will be belonging to a particular activation group.

3. Rule flow-group: this is similar to the agenda group. This is primarily used in the JBPM process to process rule flows.

13. What are the benefits of using rule engines in business project management?

Ans: Below are the important benefits of using rule engines in business project management such as;

1. Offers high flexibility

2. it’s very easy to learn

3. Helps to reduce the intricacy

4. Reusability

14. How to remove objects from the Knowledge session?

Ans: By using the retract method to remove the object from the knowledge session.

15. What is the restriction in java code?

Ans: In drools, the user cannot use the java code inside the “when” part of the rules, and it can also be used in the “then” part.


In this blog, I have tried my best to explain the top 15 important drools interview questions and answers asked by any top recruiter. Learning HKR’s drools interview questions and answers will help you to gain knowledge and crack any interview. These interview questions are designed for both basic to experienced professionals.

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Research Analyst
As a Senior Writer for HKR Trainings, Sai Manikanth has a great understanding of today’s data-driven environment, which includes key aspects such as Business Intelligence and data management. He manages the task of creating great content in the areas of Digital Marketing, Content Management, Project Management & Methodologies, Product Lifecycle Management Tools. Connect with him on LinkedIn and Twitter.

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