Microsoft making RSS a two-way street

Microsoft Corp. is extending the popular RSS 2.0 Web syndication format to make it "multidirectional," allowing it to be used for synchronizing information such as contacts and calendar entries across different applications, the company said.

RSS 2.0 is best known as a way to let Internet users subscribe to content from Web sites that support RSS (Really Simple Syndication) feeds. When content on a site is updated, the RSS feed informs the subscriber, often with a summary of the updated content and a link to it.

Microsoft is developing a set of extensions to RSS so that it can be used for exchanging and synchronizing content that is updated by two or more parties. Its goal is to take what is essentially a one-way publishing mechanism and make it multidirectional.

The company published version 0.9 of the specification, called Simple Sharing Extensions (SSE) for RSS 2.0, on its Web site earlier this month and is seeking feedback for a final version.

To understand what the extensions hope to achieve, imagine two PC users who wish to share and coedit a list of items using an RSS feed. Both people publish their lists using RSS with the sharing extensions, and both also subscribe to the other's feed.

Whenever either of the two updates their list, the changes are added to their feed and incorporated into the list of the other subscriber.

The extensions "enable feed readers and publishers to generate and process incoming item changes in a manner that enables consistency to be achieved," Microsoft said. "In order to accomplish this, SSE introduces concepts such as per-item change history (to manage item versions and update conflicts) and tombstones (to propagate deletions, and un-deletions)."

The specification could be used to keep contact lists synchronized across a user's various devices, such as a PC, PDA (personal digital assistant) and mobile phone. Or it could be used by family members (or co-workers) to synchronize entries they wish to share from their personal calendars, explained Ray Ozzie, Microsoft's recently hired chief technical officer, in a posting on his blog.

Ozzie's involvement in SSE is no surprise -- he created Lotus Notes, which lets workers update and synchronize calendars, documents and other files with each other. Notes was part of the inspiration for SSE, Ozzie said.

After joining Microsoft he met with some of its product teams, including Exchange and Outlook, and thought about ways of synchronizing information among Microsoft products, as well as with those of other companies, he wrote. Soon after, SSE was born.

"In just a few weeks time, several Microsoft product groups ... built prototypes and demos, and found that it works and interoperates quite nicely," Ozzie wrote. It's too early to say which Microsoft products will use SSE, and code won't be released until version 1.0 is ready at a future, unspecified date, he said.

Microsoft has a checkered past when it comes to "extending" technologies it does not own, raising inevitable questions about its intentions with RSS 2.0. Sun Microsystems Inc., for example, sued Microsoft for extending Sun's Java technology in a way that prevented some Java applications from running properly on Microsoft's software.