A family living on an old farm is a nice picture, isn't it? The farming started our civilisation and you can know farm as basic food production unit of many strategy games. Family farm is a living system - closed economy where business joins the family side of life in every single minute. Could be risky to make the farming fun. But if something would go wrong, we can always turn characters into zombies and let them fight with plants. Everything with zombies is popular!
Of course we know Harvest Moon and these series could be considered as our inspiration. Harvest Moon game design is influenced by (japan) RPGs. You have character, inventory with items, tools, NPCs, quests, etc. When they started work on the series in '95 for SNES there was almost no other choice of underlying game mechanics. More than ten years after that we were in a better position when searching for game mechanics. We experienced rise and fall of tycoons, admire and hate The Sims, enjoy modern board games and have many other minor influences.
Then in 2009 I started to recieve "cute spam" from my infected farming friends... I finish my case saying that we are working on a farming game, not addictive farming application. No fun for cow clickers here!