Drools Interview Questions

Q. What is Drool?
Drools is a free and open source project licenced under the Apache License 2.0 and it is compatible with any JVM and available in Maven Central Repository also.

Drools is a BRMS (Business Rules Management System). It includes a Business Rules Engine (BRE), a web authoring and rules management framework (Drools Workbench), complete runtime support for Decision Model and Notation (DMN) models at Conformance level 3, and a core development Eclipse IDE plugin.

It is written in 100% pure Java, runs on any JVM and is available in the Maven Central repository too. The Drools assists you in separating and reasoning over logic and data in business processes. It has a forward and backward chaining inference-based drools rules engine that supports forward and backward chaining.

Q. What is the Drool Rule Engine?

Drools is a Rule Engine or a Production Rule System that implements an Expert System using a rule-based approach. Expert systems are information-based systems that process acquired knowledge into a knowledge base that can be used for reasoning.
A Production Rule System is Turing complete, with a focus on knowledge representation to express propositional and first order logic in a concise, non-ambiguous and declarative manner.
The brain of a Production Rules System is an Inference Engine that is able to expand to a large number of rules and facts.
A Production Rule is a two-part structure that uses first-order logic for reasoning over knowledge representation.
A Rule Engine allows you to specify “What to Do” rather than “How to Do It”.

Q. Explain the Architecture of Drools?
The working of Drools architecture is as follows:

Production Memory
The Rules are stored in the Production Memory/Rule Base.

Q. What Does Jbpm Do?

This commercial enterprise manner permits you to model your enterprise desires with the aid of describing the steps that need to be executed to attain that aim and the order, the use of a drift chart.This greatly improves the visibility and agility of your business good judgment, results in higher-level and domain-specific representations that can be understood with the aid of business customers and is simpler to reveal.The middle of jBPM is a mild-weight, extensible workflow engine written in pure Java that allows you to execute commercial enterprise procedures the usage of the ultra-modern BPMN 2.0 specification. It can run in any Java environment, embedded for your software or as a provider.

Q. What Are The Features Of Jboss Enterprise Web Platform?

The JBoss Enterprise Web Platform is the software infrastructure that supports the walking of BRMS additives.

Q. What Are The Features Of Jboss Enterprise Application Or Soa Platform?

It is the utility software program structure in the machine that helps going for walks of BRMS additives.

Q. Who Use The Business Rules Engine?

Drools experts use the Business Rules Engine thru Rete set of rules and Drools Rule Language (DLR).

Q. Is The Graphical Process Designer (gpd) Only Useable In Eclipse?

Is There A Way To Use It Standalone?Answer :The jBPM GPD is an eclipse plugin that goals utilization via more than one roles. Both the enterprise analyst and developer are capable of use the identical device in extraordinary ways. The main reason why we suppose it is essential to combine those in one unmarried surroundings is because in many groups, these roles are executed via one person.Then it turns into very crucial that the device can help each roles and progressively shift from being a diagramming tool to an implementation tool.

Q. What Are The Advantages Of Rule Engine?

Advantages of Rule Engines:Greater flexibility: preserving your regulations right into a Knowledge base will let you adapt easily your selections while they may be changing.Easier to understand: Rules are less complicated to understand than procedural code in order that they can be correctly used to bridge the gap between enterprise analyst and builders.Reduced complexity: When embedding masses of selection points on your procedural codes it could without difficulty flip your utility right into a nightmare. On the alternative hand guidelines can deal with tons higher increasing complexity because they use a regular illustration of commercial enterprise policies.Reusability: By keeping rules are saved in one location leads to a extra reusability of your business guidelines. Also, traditional procedural code regularly impose needless versions of base rules which might be therefore more hard to reuse in different contexts.

Q. Where To Use Global Variable?

Consider a scenario, where inside the rules there may be a demand for database connection object. In this case, the DB Connection item may be inserted as a worldwide variable inside the operating reminiscence and the connection item can be visible to all of the guidelines in that DRL record.

Q. What Is Business Rules Manager?

Business Rules Manager is a centralized repository for the Drools expertise bases and has wealthy web primarily based Graphical User Interface as well as tools and editors to control big numbers of policies.

Q. What Is Global In Drl File?

Global is the keyword used in drools to outline a global variable. Global variable is the only on the way to be visible to all the guidelines internal a DRL record.Globals have to be used very cautiously in a DRL file, since the modifications in a global variable are not notified to the operating reminiscence. For example, you’re using a listing variable as a worldwide and in any rule you’re including a cost in a list and in a single specific rule, you are checking if list length() > 0, then in this example rule may not fireplace. Global variable can be used for any type of object.

Q. Explain The Difference Between String Builder And String Buffer Class?

String Builder is unsynchronized whereas StringBuffer is synchronized. So when the application needs to be run best in a unmarried thread then it’s miles better to use StringBuilder. StringBuilder is extra green than StringBuffer.

Q. What Is Meant By Drools Guvnor And Drools Expert?

Drools Guvnor is the Business Rules Manager and Drools Expert is the Business Rules Engine.

Q. How should the global variable be used in DRL file?

Global variables can be used extremely carefully in DRL file. Changes in global variable are not modified in working memory and hence care in handling them is required.

Q. What is the use of global variable?

Global variable can be used for any type of object and there won’t be any mismatch.

Q. Where global variable should be used?

Where in the rules requirements for database connection object is necessary, global variable should be used. For instance; The DB connection object could be global variable.

Q. What is not advisable in use of global variables?

Changing global value inside the rule is not advisable. Instead the value should be set from the application using the working memory interface.

Q. What is meant by accumulate in DRL Drools?

Accumulate is conditional element that was introduced in Drools version 4.0. It is used to iterate over the list of objects and help validation of data in Java operation.

Q. What is meant by Drools Recursive Rules?

A Fibonacci series is the most common example of recursion in Drools. In the Drools the implementation is carried out using the insert and modifies keywords.

Q. What are the most important parts of Recursion in Drools?

The three most important parts of in the process of implementation of recursive rules in Drools are inserting keywords in ‘then’ part, not keyword used in ‘when’ part, and ‘breaking condition’.

Q. What would be the breaking condition in Fibonacci series?

The breaking condition in Fibonacci series would be (sequence==1).

Q. Explain what are the features of JBoss Enterprise Web Platform?

The JBoss Enterprise Web Platform is the software infrastructure that supports the running of BRMS components.

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