Of course, the total economy is much more complicated than the illustration above. An economy involves interactions between not only individuals and businesses, but also Federal, state, and local governments and residents of the rest of the world. Also not shown in this simple illustration of the economy are other aspects of economic activity such as investment in capital (produced—or fixed—assets such as structures, equipment, research and development, and software), flows of financial capital (such as stocks, bonds, and bank deposits), and the contributions of these flows to the accumulation of fixed assets.[4]