How to design a rule engine?

Question

I'm supposed to create a simple rule engine in C#. Any leads on how I can proceed?. It's a minimalistic rule engine, and would use SQL server as the back end. Do we have any general blueprint or design patterns that generally apply to rule engines? What kind of .Net technologies can I use to design one? Any directions would be helpful. Thanks.

Answer 1

If you're using .NET 3.0 or later, you can use the Rules Engine of Windows Workflow Foundation without having to acutally use Workflow.

I've done this on a project, and you can use SQL or XML as the backend, and it works great. You can use the IDE that comes with the Workflow examples and put it in your own apps. It's excellent.

Answer 2

1. I cannot believe you would implement your own considering there are so many available commercially and open source.

2. I recommend taking a look at InRule as a great commercial option that is reasonable priced, or NxBRE in the open source space.

Answer 3

You can also try http://rulesengine.codeplex.com/

Answer 4

What kind of Rule engine you looking for? For styling practices? If so, go check out StyleCop. Not the answer, but there might already be something out there for you.

Answer 5

Are you given any indication on method? (ie if this is supplemented by course material what are you currently learning?) If this is meant to be a fairly basic system you might find success looking into to Deterministic Finite State Machine and Nondeterministic Finite State Machine

Answer 6

If you have business analysts to program the high level rule engine, then fine - pick one of the before-mentioned rule engines or roll your own (including workflows). If not, then just code your business logic in code and if you ever need to hire business analysts and redo the system, you're in a good place to be.

Answer 7

If you want to write your implementation something like this...

[TestMethod]
public void GreaterThanRule_WhenGreater_ResultsTrue()
{
    // ARRANGE
    int threshold = 5;
    int actual = 10;

    // ACT
    var integerRule = new IntegerGreaterThanRule();
    integerRule.Initialize(threshold, actual);

    var integerRuleEngine = new RuleEngine<int>();
    integerRuleEngine.Add(integerRule);
    var result = integerRuleEngine.MatchAll();

    // ASSERT
    Assert.IsTrue(result);
}

... or this...

[TestMethod]
public void GreaterThanRule_WhenGreater_ResultsTrue()
{
    // ARRANGE
    int threshold = 5;
    int actual = 10;

    // ACT
    var integerRule = new IntegerGreaterThanRule(threshold);

    var integerRuleEngine = new RuleEngine<int>();
    integerRuleEngine.ActualValue = actual;
    integerRuleEngine.Add(integerRule);

    // Get the result
    var result = integerRuleEngine.MatchAll();

    // ASSERT
    Assert.IsTrue(result);
}

... then maybe check out my simple rule engine here: http://www.duanewingett.info/2015/01/21/SimpleCRuleEnginePart1TheRuleEngine.aspx