In an effort to build a larger community of developers for its Flex environment, Adobe Systems said Thursday it plans to open-source the Flex software development kit (SDK), designed to let developers build multimedia-rich Internet applications, by the end of the year.

The SDK includes the two developer languages used to write Flex applications, MXML and ActionScript 3.0; class libraries; components such as user-interface controls and layout containers; and the code compiler, which is required for developers to write Flex applications. Adobe will release all of these elements under the Mozilla Public License by the end of the year, said Jeff Whatcott, vice president of product marketing.

The move is part of Adobe's makeover to position itself as an ally to open-source developer community, Whatcott said. The company hopes this strategy will help Flex become more widely used, as it is an integral product for Adobe's strategy to maintain and increase its position with developers in the rapidly growing rich Internet applications market.

There are several market forces at work driving this strategy. Traditionally, Adobe has been seen as a more proprietary niche player in the digital document-creation and Web development tools space. For example, Adobe's ubiquitous portable document format (PDF), while available for free, has never been available to the community as a standard. Adobe recently submitted PDF to the International Organization for Standardization (ISO) to change that as part of its more open style.

Acquiring Macromedia, the original Flex creator, in 2005 helped Adobe seem more developer-friendly because of that company's Java-based software portfolio and popularity with Web developers. But even then Adobe acquired a set of proprietary tools such as Flash -- on which Flex is based -- and Dreamweaver, which have a loyal following but are not specifically aimed at pulling in open-source loyalists.

Adobe needs the open source community for another reason: Microsoft is encroaching on their territory with its forthcoming Expression toolset and recently unveiled Silverlight technology for deploying rich Internet applications from the browser. Opening up Flex could help Adobe earn a critical mass of developers it will need to fend off Microsoft going forward.

Joe Berkovitz, chief architect with Allurent, a company that has built software for rich Internet commerce applications based on Flex, said open-sourcing the Flex SDK will serve both developers and Adobe well.

"[Flex] is a young platform, and because Adobe has had the source exposed for some time, developers that work closely with it will have a lot of insight on how to make [Flex] better," Berkovitz said.

Adobe, too, will gain from differentiating itself from Microsoft through its open-source affiliation, he added.

"It takes the comparison between [Microsoft's competing technologies] WPF (Windows Presentation Foundation) and Silverlight and Flash/Flex to a different level," Berkovitz said. "It's not just what features are best ... but what process are each of the platforms following as they evolve. A process based on open source is going to be inherently more powerful and scale better."

The move to open-sourcing the Flex SDK will be a gradual transition, Whatcott said. Currently, the SDK is available for free from the Flex developer site, and developers can modify the source code for any of the elements, but not submit changes back to other Flex developers.

Beginning in June, developers will be able to view Flex's bugs in a public bug database and receives fixes for those bugs daily, Whatcott said. They also will be getting new code drops every day as Adobe readies the next version of Flex, which is currently in its alpha stage of development.

Finally, by the end of the year, Adobe will have established on the Flex Web site a central code repository for Flex that's public and will allow developers to contribute changes back to the broader Flex community.

The entire Adobe Flex portfolio includes the SDK, the Flex Builder development environment and Flex Data Services, J2EE-based technology that connects the other Flex elements to servers on the back end. Adobe will continue to sell Flex Builder and Flex Data Services for a fee and is not open-sourcing those components of the package, Whatcott said. However, developers don't need Flex Builder to developer Flex-based applications, he said. They can use any text-editing tool or IDE, including common Java IDEs and Microsoft's Visual Studio.Net.