Kogito, ergo Rules — Part 1: Bringing Drools Further

The Kogito initiative is our pledge to bring our business automation suite to the cloud and the larger Kubernetes ecosystem. But what does this mean for our beloved rule engine, Drools? In this post we introduce modular rule bases using rule units: a feature that has been experimental for a while in Drools 7, but that will be instrumental for Kogito, where it will play a much bigger role. This is the first post of a series where we will give you an overview of this feature (read part 2)

Bringing Drools Further

Drools is our state-of-the-art, high-performance, feature-rich open source rule engine. People love it because it is a swiss-army knife to the many problems that can be solved using rule-based artificial intelligence. But as the computer programming landscape evolves, we need to think of ways to bring further Drools as well. As you may already know, Kogito is our effort to make Drools and jBPM really cloud-native, and well-suited for serverless deployments: we are embracing the Quarkus framework and GraalVM’s native binary compilation for super-fast startup times and low memory footprint; but we are not stopping there.

The way we want to bring further Drools evolution is twofold: on the one hand, we want to make our programming model easier to reason about, by providing better ways to define boundaries in a rule base with a better concept of module; on the other hand, the concept of modular programming dates back at least to the 1970s and to Parnas’ original seminal paper. Needless to say, if our contribution stopped there, we would be bringing nothing new to the plate. In the last few years, computing has evolved, slowly but steadily embracing the multicore and distributed revolution; yet, to this day, many general-purpose programming languages do not really make it simple to write parallel or distributed programs. rule-based programming system we have the chance to propose something different: a rule engine that is great when stand-alone, but outstanding in the cloud.

Modular Rule Bases. As you already know, Drools provides a convenient way to partition set of rules into knowledge bases. Such knowledge bases can be composed together, yielding larger sets of rules. When a knowledge base is instantiated (the so-called session), rules are put together in the same execution environment (the production memory), and values (the facts) are all inserted together in the same working memory.

This model is very simple and powerful but in some senses it is also very limited. It is very simple, because, as a user of the rule base, you just worry about your data: the values are inserted into the working memory, and the engine does its magic. It is very powerful, because, as a rule author, you can rely upon the rules you have written to realize complex flows of reasoning, without worrying about how and when they will trigger.

At the same time, such an execution model lacks all of the principles, that over the years we have been learning are good programming practice. For instance, there is no proper notion of a module: it is not possible to perfectly isolate one rule from another, or to properly partition the working memory. As the rule base scales up in complexity, it may become harder to understand which rules trigger and why. In some senses, it is as if you were programming in an odd world where proper encapsulation of state does not exist, as if years of programming language evolution had not happened.

Object-Oriented Programming. The term object-oriented programming has been overloaded over the years to mean a lot of different things; it has to do both with inheritance, with encapsulation of state, with code reuse, with polymorphism. All these terms get often confused, but they are not really related: you can reuse code without inheritance, you can encapsulate state without objects, you can write polymorphic code without classes. Very recent, imperative programming languages such as Go and Rust do not come with proper classes, yet they support a form of object-orientation; there is even a beautiful 2015 talk from C++’s dad, Bjarne Stroustrup, showing how his child supports object-orientation without inheritance.

Alan Kay, who fathered the term in his Smalltalk days at Xerox, in his inspiring lecture at OOPSLA 1997 said «I made up the term "object-oriented", and I can tell you I did not have C++ in mind». In fact, the idea of objects that Alan Kay pioneered was more similar to the concept of actors and microservices. In proper object-oriented programming, objects encapsulate their internal state and expose their behavior by exchanging messages (usually called methods) with the external world.

Today actor systems have seen a renaissance, message buses are very central to what today we call reactive programming, microservices are almost given for granted. So, we wondered, what would it mean for Drools to become a first-class citizen of this new programming landscape?

Kogito, ergo Cloud

In the next post we will see our take on rule-based, modular programming, using rule units. Rule units will provide an alternative to plain knowledge base composition and an extended model of execution. We believe that rule units will make room for a wider spectrum of use cases, including parallel and distributed architectures. Stay tuned to read how they fit in the Kogito story, and the exciting possibilities that they may open for the future of our automation platform.

Kogito, ergo Rules — Part 1: Bringing Drools Further