I understand offer flow rules are executed by a Program internally and is not referrenced exclusively anywhere in the strategy rule.However if a group has more than one offer flpow then how the strategy decides which offer flow to pick. Can someone explain the logic?
Your query is a bit unclear. So, I'll just explain the concepts and hopefully that should clarify.
A Strategy identifies zero, one or more propositions depending on how you have designed the Strategy. In Pega Marketing a proposition is an Offer (Offer flow + proposition properties).
At run-time, a Program executes the Strategy for every customer in the Starting population which results in a list of customers and the Offers selected for each of them. If a customer qualifies for more than one Offer, then there will be more than one row in this result set for that customer.
In the next step, the Program executes the Offer flows for each customer/offer combination in this result-set. For example: If a customer qualifies for both 'Free iPhone 6 upgrade' and '15% Discount on Headset' offers, the Offer flows for both these Offers will be executed for that customer.