When we want to design a mission sub-system like in the The Ville or Sims Social, what kind of design pattern / idea would fit the best? There may be relation between missions (first do this then this etc...) or not. What do you think sims social or the ville or any other social games is using for this?

I'm looking for a best-practise method to contruct a mission framework for tha game. How the well-known game firms do this stuff for their large scale social facebook games?

• Giving missions to the players and wait players to complete them. when they finished the missions, providing a method to catch this mission complete events considering large user database by not using server-side not so much to prevent high-traffic / resource consumption.

how should i design the database and server-client communication to achive this design condidering this trade-off.