, and generally, ISPs (Internet service providers), for actions that he says could significantly hamper the potential of the Web.

"If we, the Web's users, allow these and other trends to proceed unchecked, the Web could be broken into fragmented islands. We could lose the freedom to connect with whichever Web sites we want," he wrote.

He says social-networking sites including Facebook, LinkedIn and Friendster threaten the Web's universality. Such sites assemble data such as users' birthdays, e-mail addresses and likes into databases, reusing the information to provide value-added services. The hitch is that such services are available only within their sites, he said.

"Each site is a silo, walled off from the others. Yes, your site's pages are on the Web, but your data are not. You can access a Web page about a list of people you have created in one site, but you cannot send that list, or items from it, to another site," he notes.

"The more this kind of architecture gains widespread use, the more the Web becomes fragmented, and the less we enjoy a single, universal information space," he said.