It's useful to think of capital as a store of time and labor. Let's consider money outside our current banking system. In The Ascent Of Money: A Financial History of the World by the Penguin Group, Niall Ferguson discusses the history of money and credit in human civilization (you can find it at http://www.amazon.com/The-Ascent-Money-Financial-History/dp/0143116177). This approach lets us consider how societies use capital to distribute wealth. Among other things, he argues that the evolution of credit and debt is as important as any technological innovation in the rise of a civilization. I've mentioned this to highlight the purpose of finance and the fact that money and finance have existed across many banking systems, including before our current one. It's important that this approach not be ideological. I want to frame the core purpose and function of a bank and flesh out the mechanics of money flows.

When programming (computers), the first task is to build an understanding of the systems we're trying to model and the problems that we are trying to solve. As such, let's distill some central notions of money and how it fits into the banking function. This is written in the spirit of banks simply becoming information processes and looking more like software companies. Technology produces alternative mediums of capital, such as cryptocurrencies, for example, bitcoin (you can find more about this at http://en.wikipedia.org/wiki/Cryptocurrency). But this concept is outside the scope of the book. I make the point to emphasize the seismic effect that software is having on finance and all modern professions. I will try to describe the context and constraints within which such banking software must operate.

Money is a medium of exchange, unit of account (divisible, fungible, or of a specific measure or size), store of value, and a standard of deferred payment. In economics, money creation is the process by which the money supply of a country or a monetary region (for example, the EU) is increased. Changes in the quantity of money may be caused due to the actions of a central bank, depository institutions (principally commercial banks), or the public. However, the major control rests with a central bank. The actual process of money creation takes place primarily in banks (refer to https://archive.org/details/ModernMoneyMechanics and http://upload.wikimedia.org/wikipedia/commons/4/4a/Modern_Money_Mechanics.pdf). In the U.S., the money creation process centers around the US Federal Reserve. So, a central bank may introduce new money into an economy by purchasing financial assets or lending money to financial institutions or governments. The majority of money in our modern economy is created by commercial banks who give loans or demand deposits.

There's much more to take into account. However, this context allows us to begin considering how to faithfully represent credit levels and flows within and between bank and bank-like entities. We can also start thinking about a commercial bank's core functions and constraints, and the systems it should implement to perform all of these.