Hi William,
Kudos for an excellent post office example. This example helped me redesign my interface.
I think the 2 possible scenarios for this example are :-
1. Customer arrives at stamp counter and asks for a particular country stamp. In response to this query, the person at counter gives a response back with the desired stamp. Customer sticks the stamp on the enevelope and then asks for cost. The counter person responds back with cost. Customer hands over the money and counter person gives back change if any. Finally customer hands over the envelope to be mailed and counter person takes the mail and customer goes away.
2. Customer arrives at stamp counter, gives envelope to counter person and tells him to mail to a particular country. To be really efficient, he also hands counter person a $100 bill. The counter person does the processing (stamping the envelope, giving back
any change etc).
Obviously in option 1 there is lot of fine grained message exchange happening
vs option 2 where the transaction takes only one interaction.
Option 1 took a lot of interactions because of a) the overall process followed in option 1 b) the responsibilities divided between customer and counter person and c) lack of pre-hand knowledge about transaction (like the cost of the stamp).
Option 2 though has possible exception flow in case customer decided to give
the counter person a quarter instead of a hundred dollar bill and the stamp cost was
10 dollars. This would increase number of interactions between customer and counter person.
I guess by 1)changing the process, and 2) by making the exchanged message more intelligent the above reaons a) and b) can be improved or eliminated. which
leaves point c which involves invoking business rules.
So , i guess with new improved process, the above example would look like :-
1. Customer goes to stamp counter and asks for stamp cost for a particular country.
Counter person responds with cost. Customer hands the money and envelope and
counter person hands back change if any.
2. Customer has account with postal service and in this case customer just walks to the counter and hands the enevelope with a lil note on envelope pointing to country and walks away. The counter person accumulates enevelops from different customers and then on free time charges account, stamps enevelops and mails them and sends a reciept to customers.
Cheers,
Maninder
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