linkedin platform logoLinkedIn aims to be an even more central part of your professional identity, by expanding its platform today with the site developer.linkedin.com.

The Mountain View, Calif.-based professional networking site already offers a platform for third-party developers, allowing them to build widgets and apps that run in LinkedIn itself. What it’s announcing today is another piece of that platform, one that’s arguably more exciting — the site is allowing developers to access your LinkedIn data from their own external business applications. The idea is that LinkedIn could become your professional identity across applications, in the same way Facebook wants Facebook Connect to be your social identity across the web.

“We’re very opinionated,” said Adam Nash, vice president of search and platform products. “We believe that any business application that someone builds in 2010 that doesn’t integrate with us is going to be an anachronism.”

You can get some sense of what LinkedIn has in mind with already-announced integrations like its Social Connector in Microsoft’s email and contacts program Outlook. LinkedIn is adding new partners today, including Twitter application TweetDeck, simple blogging startup Posterous, and BT-owned voice-over-Internet company Ribbit. Other application-makers can now register at the developer site.

This move is more consistent than LinkedIn’s previous platform features with how I, at least, use the site. I’m much more interested in accessing my LinkedIn profile and data regardless of what application I’m using than I am in tinkering with a bunch of different applications on the site itself.

Nash said LinkedIn is opening its data via “about a dozen” application programming interfaces (APIs), which will enable three types of applications: Apps that let users view their LinkedIn profiles; apps that allow users to take actions, such as sending a message to a LinkedIn contact; and apps that access LinkedIn’s search. Users will log into LinkedIn using the OAuth authentication standard.

LinkedIn says it has more than 50 million users.