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copied!<p>A rule engine is little more than something that executes declarative statements. They come with two primary advantages (that I see):</p> <ol> <li>Your business logic is maintained from a single place instead of being sprinkled throughout application code. Technically, a well-designed application should already do this with the architecture, regardless of a rule engine being present or not.</li> <li>You need to worry [less] about dependencies between declarative statements. The rule engine should be smart enough to decide the order to run rules based on dependencies. You may find that some rule engines support a sequential ordering of rules within a ruleset or calling rulesets (groups of rules) in a particular order, but this isn't really in the spirit of declarative programming. Many rule engines use Rete (an algorithm) to decide when to schedule the execution of declarative statements.</li> </ol> <p>I suspect most, if not all, rule engines add more overhead than if you were to write the best possible program that doesn't use a rule engine. This is similar to how writing code in assembly is generally faster than a compiler (but you usually don't write assembly because it's more convenient and productive to use higher-level abstractions).</p> <p>If you were to stop here, then you would probably use programmers to maintain rules and use a rule engine as a convenient way to build a business logic tier in your application. Some rule engines offer something called templates that let you define templates for rules. The advantage here is that non-technical users are supposed to be able to write their own rules and modify existing rules.</p> <p>A rule engine is one more tool in your tool chest that, when used properly, can be valuable.</p>

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