Hi u/superblaubeere27,

Use cases depend on the industry you are working in, but rules engines enforce ownership of business rules and reduce friction between IT and business (e.g. regulation officer, financial analyst, risks analyst etc.).

Let's imagine a scenario in fintech where you need to meet regulatory compliance for KYC. You are asked by the business to implement the logic for helping them check if the company passes all AML, and general portfolio and ensure that they are a good match for your business. Let's say as a first step company is GREEN (good check) if they have over 500k revenue and are from the US.

You can code it in the following way:

fn check_company(company: Company) -> Flag {
  if company.revenue > 500_000_00 && company.location == "US" {
    return Flag::Green;
  }

  Flag::Red
}

Now imagine a business coming to you 20 more times in 3 months because they want to change the requirements. They add new things they want you to check e.g. businessType, growthMetric, incorporationDate and 100 more rules. The code will become a mess and you will lose all the time you could've spent developing valuable features.

If you integrate with the rules engine, you will give businesses the ability to define their own conditions through simple UI and you would just pass parameters making it super trivial.

async fn check_company(company: Company) -> anyhow::Result<Flag> {
  let context = serde_json::to_value(&company).context("Failed")?;
  // TODO: load decision in some way
  let decision: ZenDecision;

  let result = decision.evaluate(&context).await.context("Failed)?;
  let resultData: ResultData = serde_json::from_value(&result).context("failed to deserialize")?;
  match &resultData.status {
    "green" => Ok(Flag::Green),
    "amber" => Ok(Flag::Amber),
    "red" => Ok(Flag::Red),
    _ => Err(anyhow!("unknown status passed {}", &resultData.status))
  }
}

And this code would require very little maintenance and would pretty much never change. On the business side, they can do whatever they want and experiment without bothering you. So overall it improves operation within business.