How respective rules are loaded when stream gets payload

For instance, I have a stream called demo and there are 2 rules created for the same (rule1,rule2).
When i send data to "demo",  how rule engine understand this time  rule1,rule2 should execute AND how rule is loaded from db ?

I had go through the source code to understand , since i'm not that good at golang , i didn't get the understanding well.
