Rules Engine Design Questions

Question

Rules Engine Questions:
1. Rules are processed in the order they are created in dictionary file if the priorities are the same. Is it true?
for eg: if the order you see on the screen in rules dictionary window is:
     rule1 --> set var1 = 10
     rule2 --> set var1 = 20
     rule3 --> set var1 = 30
     rule4 --> set var1 = 40
     rule5 --> set var1 = 50
     result would be 50
2. I want to use the rules engine for validations.
Eg: Can we check for the requiredness of xsd validations using rules engine? or this should be done else where?
eg:
If my xml is below, then can I use rules engine to check
<Firstname>
<LastName> and
<Address1>
for emptyness and pass back saying that the validation failed because <LastName> and <Address1> are empty.
<Customer>
     <Firstname>aaa<Firstname>
     <LastName> <LastName>
     <Email>ccc<Email>
     <Address>
          <Address1> </Address>
     </Address>
I have a response xml:
     <ValidationResult>
          <Result>Failed<Result>
          <Message>all required fields are not present<Message>
     <ValidationResult>
So my rules should be
     check for <Firstname>
          Assert new ValidationResult ('success', ..)
     check for <LastName>
          Assert new ValidationResult ('failed', ..)
     check for <Email>
          Assert new ValidationResult ('success', ..)
     check for <Address1>
          Assert new ValidationResult ('failed', ..)     
and since last rule is failed, will rules engine send back failed? or what is the strategy for order of rules that get fired?
For the above scenario what would be the best design solution?

Answer 1

This is a complicated question but I will try my best to give you the best solution:
#In answer to your question regarding the order that rules fire unless you use priority you cannot garantee the order that the rules fire. The Oracle rules engine uses the Rete algorithm to establish the order in which to fire the rules and this is generally based upon the data passed into the rules. Therefore if the result of rule 4 may effect rule 1 then the rules engine will run rule 4 before rule 1.
The scenario you have provided is slightly different however and I woudl suggest the following.
Instead of passing out a single result from your ruleset pass our an array of results meaning you could effectively run all your rules and pass out all rules that failed. Be wary of checking for nulls however because if nothing is passed into a field then the rules engine will not create that element in the rules fact and the rule will never fire.
To create a array of results you will need to create a function which creates the result fact for you and then addes each result in turn.
If you woudl like more information let me know and I will help out as much as I can.