The Web’s infrastructure can be thought of as composed of four horizontal layers; from bottom to top, they are the transmission medium, the computer hardware, the software, and the content. … I am more concerned about companies trying to take a vertical slice through the layers than creating a monopoly in any one layer. A monopoly is more straight forward; people can see it and feel it, and consumers and regulators can “just say no.” But vertical integration — for example, between the medium and content — affects the quality of information and can be more insidious.

– Weaving the Web, p130