If you don't want to use "send message and wait for reply", what about registering and braodcasting? I like it as it's general and non blocking (though if you do need the process to block, send and wait for reply makes more sense).
Basically, whoever wants to know when data is changed "registers" in the data actor; whenever data is changed, the data actor sends the updated data to all registered elements. The boradcast can also be via HTTP etc. if you want.
Thanks,
Danielle
"Wisdom comes from experience. Experience is often a result of lack of wisdom.”
― Terry Pratchett
