Creating custom rules in PRPC – Introduction

Pega Rules Process Commander is such a wonderful product. It is built so elegantly with layer upon layer of abstraction so that a normal business user can easily change the runtime behavior in order to adjust to the changing business conditions without going through a typical development cycle. At the same time it is a mixture of J2EE technologies, bunch of browser based thin client technologies and more importantly a wonderful design that has the unique feature of "ability to be extended in multiple layers", where a person could not distinguish whether a feature is out of the box or custom made. All these are possible due to the initial wonderful design of PRPC.

One of the best things that the designers of PRPC have done is, even though there are multiple layers of abstraction, they have given us, the end developers a chance to extend the core product through custom rule creation.

Before creating custom rules first let's get a clear understanding to the question "What is a rule?". If you can remember the Fast Track training that you have attended, you may remember the phrase "Everything is a rule" and how you left the Fast Track training with that in mind. but is it correct?, frankly not, technically a rule is an instance of a concrete class which is inheriting from Rule- Class. So while Decision Table / Decision Tree are rules, Operator ID / Access group are not, they are just data objects which does not have the "Ruleness" within them. So naturally the next question should be What is "Ruleness" ?

It turns out to be, when you inherit a class from Rule- class and make it concrete, all the instances of that class will get some magical powers as opposed to instances of a normal class. Exactly 4 magical spells which as a unit can be called as Rule Resolution options.

More importantly you as the developer can adjust the "Ruleness" according to your requirements. You get to choose the Rule Resolution options for your custom rule. You get to choose how your custom rule should behave at runtime. 

So far we have understood the concepts of Rule and "Ruleness", now let's see the big question "What is a custom rule" 

Custom rule is a rule which describes a process / execution pattern which does not available as out of the box rule in PRPC.

One of the unique features of a custom rule is that after the initial creation,  it can be used by other developers as if it were out of the box rule.

Basically there are two flavors when comes to creating and executing rules in PRPC

1. Using an Activity to interpret an instant of a rule type. (e.g. Rule-Connect-SOAP)

2. Using the “First Use Assembly” process turning the rule instance in to a java class file and then let the PRPC engine to execute (e.g. Rule-Declare-DecisionTable)

In the next post I will explain the method one, by creating a rule that connects to an excel file to read and write data (Let's call the new rule Connect-Excel ). Here is a sneak preview of how the rule looks like.