"...the routine for making a cake involves subroutines like pour, mix, and bake. These operations often will require particular inputs, like flour, sugar, and a stove. In turn, virtually all complex routines are linked with other routines that must be effected in order to make them possible, or to enable them to create value. Thus, a cake-making routine presupposes that the necessary ingredients and equipment are at hand, and the acquisition of these at some prior date requires its own “shopping” routines. And still further back in the chain of activity, the inputs themselves needed to be produced, in a form that meets the requirements of cake-makers."
Nelson, R.R. and Nelson K. (2002). Technology, institutions, and innovation systems. Research Policy 31: 265–272.