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I was looking through some game AI and general AI texts and a couple of them touched on using the Rete algorithm for rule systems. Is this commonly used? I'm having trouble justifying the extra effort to create a complex Rete decision tree versions a simpler straightforward one.

Is this a worthwhile thing to implement for when my application (or future applications) grow in scale?

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I've never seen a Rete algorithm in a game. – Crashworks Apr 17 '12 at 22:37
up vote 6 down vote accepted

The answer is completely dependent on your actual game. The correct answer is going to be, "if you need them, you have to implement them, and if you don't, then don't bother."

A vast majority of AAA games don't have any kind of decision tree at all, so by all means, implement whatever you need for your specific game design, and no more.

Just remember that with games, good AI has nothing to do with making the AI actually intelligent. It's all about making the AI seem human and believable and interesting. 90% of that is done with animations and voice acting, not AI. Your AI can be dumb as mud, but if the AI actors choreograph their "reactions" and are given personality with voice and characteristic movements then the players will be deeply engaged with them.

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I assume you're talking about "cinematic" AI, but the OP - about action/combat. Sweet voice and nice acting won't make up for hard opponent. – joltmode Apr 15 '12 at 11:17
I very much agree with your first paragraph, am ambivalent of your second paragraph, and -1 for your last paragraph. – jhocking Apr 15 '12 at 12:47
+1 for the last paragraph, most people have no idea how much animations (inc. audio) contribute to player perception of good AI. – user744 Apr 15 '12 at 14:58
Not sure what to tell you guys. It's true. Players don't see or notice combat choices. They have no idea what an AI is thinking. Sure, if the actor is a complete goofus that runs into walls and ignores the player it sucks, but if the AI is just randomly wandering a level and using a basic action list to make decisions, the player is highly unlikely to ever notice the difference. Unless you're specifically dealing with a tactical shooter or RTS or something that is literally about nothing but tactics. I'm hardly the first person in the game dev industry to point this out. :) – Sean Middleditch Apr 16 '12 at 3:17

Rete itself can be heavy, because it's determining all partial matches for all rules, regardless of whether those eventually execute or not. Depending on the type of rules you have, LEAPS may be a better algorithm to implement.

For bonus points, if you have the time it is possible to develop an algorithm that merges the benefits of thte LEAPS algorithm with the Rete implementation.

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