App Developer Wants to Learn Trading

I'm an App Developer who’s done desktop apps for everything from Manufacturing to Medical to Law Enforcement. Recently I did a simple App for Forex and Swaps traders (under contract where I didn’t create the specs and I signed over the IP so the app is not mine).

I enjoyed learning the Trading domain but I realize I don't know it well enough to do apps on my own. Right now I need someone who does it every day for a living to tell me what is needed and what would be truly useful – the specs.

I'm about to start delivering some mobile Apps (Windows Phone and Windows 8 first; because Microsoft is practically paying developers to do it now) So I want to learn the Trading business as best as is possible without actually doing it.

I read "Options Futures and Other Derivatives" by Hull and that was great but very academic and doesn't get into the down and dirty of the day to day on the trading desk.

At the other end of the spectrum I read "Currency Trading for Dummies" and found it better than I expected but it's too focused on the Spot market and Day trading from the home, not Forwards and the other stuff the big boys do at a trading desk.

Can someone recommend a good book about the mechanics of a trading desk? You know, stuff like; “How do trades get settled?”, “How do you know when the ‘value date’ is truly determined?, “ what’s a ‘double trade date’ – and why should you care?”, “How are ‘Rollovers’ handled”, etc. There are thousands of details like these that traders deal with every day and I want to learn them as quickly as possible