I was working with a bank in the mid-west US a few years back. They were building an on-line mortgage application that would allow brokers to submit loan applications and get real time product and pricing information. After some initial discussions it was decided to build a product and pricing engine in-house using an of-the-shelf Rules engine. I will try and summarize my learning’s about choosing the right Rules Engine below:
1) Choose a small vendor with a robust product but few clients. This would ensure a fast and accurate response to your queries and issues.
2) Expect Customizations, so get an early commitment from the vendor in terms of resources. Get somebody from the vendor side who knows the product inside-out and willing to adjust the product api’s as per your need.
3) Find out how easy it is for a layman to define rules. After all its the business who is going to manage the rules in the long term..not IT.
4) Find out how easily the product can scale. How many tps can it support. You don’t want your application to choke up due to the product that you’ve bought.
5) Find out how easily you can plug-in custom code/ui with the engine. Does it allow itself to be wrapped inside another front-end application for providing a consistent look and feel? Does it support external authentication/authorization?
6) Find out how easy it is to debug the rules. In our case, the rule engine used to generate java code which was easy to debug.
7) Find out how easy it is to simulate conditions. Having something to visualize a “what if” scenario always helps the business.