The most interesting story from Microsoft's recent Professional Developers Conference wasn't the vendor's future Longhorn operating system, but rather, Microsoft's shift away from two preoccupations of its recent past: .Net and Web services.

Microsoft isn't abandoning the .Net Framework or Web services standards in its development, hosting and interoperability environments. The .Net Common Language Runtime (CLR), .Net class libraries and growing WS-* standard suite are still expected to be core features of the future Longhorn client and server releases.

But the vendor has distanced itself from the terms .Net and Web services and has incorporated these frameworks in a broader-umbrella architecture associated with Longhorn. This uber-framework, called WinFX, refers to the new APIs and component model underlying the new operating system. WinFX, like .Net, will be supported on prior Windows operating systems through downloadable components.

WinFX will expose the functionality of an important new protocol-interoperability framework - Indigo - that sits at the heart of Longhorn. What's significant about Indigo is that it embraces, integrates and bridges the full range of middleware protocols that Microsoft has built into its operating system.

Within the Indigo environment, the Web services framework (WSF) is the dominant approach, but not the only approach, for integrating applications. Indigo encompasses all core WSF standards and protocols - principally XML, Simple Object Access Protocol (SOAP), Web Services Description Language and Universal Description, Discovery and Integration - and everything else that's being developed under the WS-* heading. But Indigo also will let older Windows-based applications interoperate with newer WinFX applications.

Indigo uses service-oriented architectures (SOA) to bridge WSF and other middleware approaches and protocols. Fundamentally, an SOA is any interoperability environment in which autonomous applications expose their interfaces through standard service contracts, publish these contracts through shared service registries and interact through exchange of messages that contain data in agreed-on schemas, such as SOAP/XML. Indigo leverages these core WSF standards to make SOAs span and bridge WSF and non-WSF middleware environments.