title: What is an appropriate data structure and database schema to store logic rules?
body: <p>Preface: I don't have experience with rules engines, building rules, modeling rules, implementing data structures for rules, or whatnot. Therefore, I don't know what I'm doing or if what I attempted below is way off base.</p>
  
  <p>I'm trying to figure out how to store and process the following hypothetical scenario. To simplify my problem, say that I have a type of game where a user purchases an object, where there could be 1000's of possible objects, and the objects must be purchased in a specified sequence and only in certain groups. For example, say I'm the user and I want to purchase object F. Before I can purchase object F, I must have previously purchased object A OR (B AND C). I cannot buy F and A at the same time, nor F and B,C. They must be in the sequence the rule specifies. A first, then F later. Or, B,C first, then F later. I'm not concerned right now with the span of time between purchases, or any other characteristics of the user, just that they are the correct sequence for now. </p>
  
  <p>What is the best way to store this information for potentially thousands of objects that allows me to read in the rules for the object being purchased, and then check it against the user's previous purchase history? </p>
  
  <p>I've attempted this, but I'm stuck at trying to implement the groupings such as A OR (B AND C). I would like to store the rules in a database where I have these tables:</p>
  
  <pre><code> Objects
      (ID(int),Description(char)) 
  
  ObjectPurchRules
      (ObjectID(int),ReqirementObjectID(int),OperatorRule(char),Sequence(int)) 
  </code></pre>
  
  <p>But obviously as you process through the results, without the grouping, you get the wrong answer. I would like to avoid excessive string parsing if possible :). One object could have an unknown number of previous required purchases. SQL or psuedocode snippets for processing the rules would be appreciated. :)</p>