Google (NASDAQ: GOOG) has cut a deal with TV ratings service Nielsen that will give the search company access to demographic data for ad targeting. Reuters says that, "Google will combine the data it receives from television set top-boxes with information that Nielsen, the dominant TV ratings company in the United States, provides on viewers by gender and age."

Google hopes that the additional layer of targeting will make its TV advertising sales package even more effective at aiming marketing messages at people who are most likely to respond to them. Today the company has access to a relatively small part of the country's ad inventory, about 14 million homes, through a deal with Echostar (NASDAQ: DISH).

Adding the Nielsen data to its current ad target system, which is used primarily on the internet, is likely to make network TV executives and sales organizations a bit tense. If the system works well, it could take the marketing and the pricing of inventory out of the hands that traditionally hold it. In other words, Google could destroy a system for selling TV ads that has been in place for decades.

It may not matter that networks and cable systems do not want Google to take away their roles as middlemen. If the new systems works, they are out of luck, and time.

Douglas A. McIntyre is an editor of 247wallst.com.