LinkedIn, an Internet social network for professionals, will open up its service on Monday to outside software developers, starting with BusinessWeek magazine, to transform itself from an online contacts and referral database into an indispensable daily tool for business users.

The company faces stiff competition from the much larger Facebook, which has attracted a zealous base of users from college students and teens to corporate professionals seeking to connect with their business networks. Unlike Facebook or News Corp's more entertainment-driven MySpace, the Web's largest social network, LinkedIn targets professionals.

The company, which was the fastest-growing social network in October, has attracted about 17 million registered users globally and about 5 million unique visitors in the United States in October. It now aims to court developers through its Intelligent Applications platform program. The program will let outside developers create software for LinkedIn as well as embed features of LinkedIn, such as finding your business contacts, directly from partner Web sites.

LinkedIn is also participating in Google's OpenSocial developer network that seeks to create a way for all developers to write software that will work on all platforms. MySpace is also a member of OpenSocial.

Unlike rivals, which have created similar programs to court the Web's vast community of software writers, developers and applications for LinkedIn will need approval by LinkedIn before they are deployed, executives said.

The partnership with McGraw-Hill's BusinessWeek will link keywords, such as company names, to the LinkedIn service. Visitors to the BusinessWeek site, who place their mouse pointers over certain keywords will trigger a pop-up box detailing how many of their LinkedIn contacts are related to the company or keyword.

A demonstration of this feature made it easy to see why rumors surfaced last month over News Corp. Chairman Rupert Murdoch's interest in buying the service, which a source told Reuters last week was simply not true. The two are in discussions for partnership opportunities, the source said earlier. Murdoch is expected to seal a $5.6 billion deal to buy Wall Street Journal publisher Dow Jones & Co Inc this week.

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