I'm using drools rules engine for my new service. I'm looking at cleaning up the rules / making it easier to write. I was hoping to use a rules framework style of coding. I.e. I want a rules file who's sole purpose is to validate the input data (i.e. input list isn't null and contains a specific value). Then when I write new rules files I can just say import this and run the validation before all other rules.
Also, I know I can load multiple rules file into the KieSession. Is it possible to tell it which order to run the rules files in, or which files to skip for each use case? The idea behind this is for performance. Let's say I load up an AWS lambda function with the rules service, I want to have all rules loaded already and have it run the specific one for the use case, instead of loading up a rules file for each call.
Thanks for the help.
You asked
Is it possible to tell it which order to run the rules files in, or which files to skip for each use case?
The answer is yes. The method to do this is called salience. The linked article is a good source to learn about this. This is important because salience can make it possible to change the order of execution of rules.
Hypothetically, let say that you have a program that process transactions based on categories. So, if category == deposit, you want to add to current balance. You have another rule that if category == withdrawal you want to subtract from current balance. BUT, you want to process deposits over withdrawals. Using salience you can guarantee that the deposits rule will fire before the withdrawal rule regardless of order of transaction.
Dependency is kind of related, but not the same. In drools, this is know as Forward or Backward Chaining depending on the order. This is all composed based on a series of facts. For example, if I was to ask a system "is my house on planet Earth?" the conclusion is reached if the following facts exist:
A direct fact linking the house location to this planet is asserted based on the rules that verify the enumerated facts above. This is done using chaining. Forward or backwards is just how these are processed (top-down or bottom-up). This is in a nutshell to the best of my recollection.