Thomson Corp. (NYSE: TOC) and Reuters Group Plc. (NASDAQ: RTRSY) joining forces to fight a common enemy: Bloomberg Plc. LP

The company founded by New York Mayor Mike Bloomberg -- and my former employer -- is the 1,000 pound gorilla in the business data market. It has gained marketshare at the expense of both Reuters and Dow Jones & Co. (NYSE: DJ) for years.

Bloomberg and Thomson were on friendly terms until fairly recently. Then, Thompson wouldn't answer questions from Bloomberg reporters about the company's earnings estimates. Eventually, Bloomberg decided to do its own polls of analysts.

The combined company may be able to erode Bloomberg's pricing power. When I first started with Bloomberg, it was a mark of status on Wall Street to have your own Bloomberg terminal. Most users that I see now share a Bloomberg to save money.

Nonetheless, Thomson and Reuters have a tough challenge. In addition to Bloomberg, there's the potential that a Rupert Murdoch-owned Dow Jones can pour money into digital publishing products that compete against offerings of the merged company. The Bloomberg threat isn't theoretical.

Though the Bloomberg terminals aren't cheap and aren't very user friendly for the untrained, it's tough to beat their functionality. Many companies have tried and failed to develop a "Bloomberg killer" over the years. Bloomberg terminals even have survived the Internet age.

But it's going to take more than just data for the combined Thomson-Reuters to thrive. More and more financial data is available on the Internet for free. Most individual investors don't need the proprietary data that these companies offer. To survive, they will need compelling content, which in the old days was called news.