Microsoft went on the offensive on Valentine's Day, openly accusing rival IBM of trying to subvert Microsoft's efforts to standardise its new document format and in turn destabilise customer choices.

"A lot of hype - and smoke-and-mirrors obfuscation - surrounds interoperability these days," Microsoft wrote in an open letter published on its website.

The letter was authored by Tom Robertson, the general manager for interoperability and standards, and Jean Paoli, general manager for interoperability and XML architecture.

The hype and obfuscation references point squarely at IBM, which was the only Ecma International member to vote 'no' in December to standardising Microsoft's Open XML file format.

Ecma International, an international membership-based standards organization for information and communication systems, approved the standardisation measure.

OpenXML is the default file format in Office 2007, and support has been back ported to Office 2003, Office XP and Office 2000.

After the Ecma vote, Bob Sutor, IBM's vice-president of open source and open standards, wrote on his blog: "The OpenDocument Format ISO standard is vastly superior to the Open XML spec.

"ODF is what the world needs today to drive competition, innovation and lower costs for customers. It is an example of a real open standard versus a vendor-dictated spec that documents proprietary products via XML. ODF is about the future, Open XML is about the past. We voted for the future."

Microsoft is seeking further standardisation of OpenXML through ISO, the International Organization for Standardization, a move that IBM is also contesting.

Microsoft claims its rival has led a campaign to subvert OpenXML standardisation at the ISO and is trying to prevent the format from being judged on its technical merits.

The open letter states: "This campaign to stop even the consideration of Open XML in ISO is a blatant attempt to use the standards process to limit choice in the marketplace for ulterior commercial motives - and without regard for the negative impact on consumer choice and technological innovation."

IBM added more fuel to the fire Monday when it released what it calls the Open Client Solution, an Eclipse-based cross-platform desktop client that features a set of collaboration components including a document editor that supports ODF but not OpenXML.

By Wednesday, Microsoft had heard enough.

"Microsoft has determined that it is important to shine a bright light on IBM's activities that will have a negative impact on the IT industry and customers, including taking concrete steps to prevent customer choice, engaging in hypocrisy, and working against the industry and against customer needs," a company spokesman said via email. "Microsoft will continue to be public in identifying the ways that IBM is trying to prevent customer choice."

In the open letter, Microsoft outlines its work on interoperability issues over the past year, including creation of its Interoperability Executive Customer Council, made up of senior CIOs, and the Interoperability Vendor Alliance, which worked with JBoss and Novell to build interoperability among their products.

On Monday, Microsoft and Novell outlined progress in their relationship in terms of virtualisation technology and integration of an open source translator technology that works between OpenXML and ODF.
That work, however, is drawing heat from more than IBM.

Some open source advocates have gone as far as to call for a boycott of Novell, which said it will include the open-source OpenXML translator in its next version of OpenOffice.

In its letter, Microsoft directly addresses document formats and XML, saying: "We believe that Open XML represents an exciting advance toward achieving the original vision of XML, where broad interoperability allows documents to be archived, restructured, aggregated and re-used in new and dynamic ways."

OpenXML is a departure from historic Microsoft practices with its Office file formats, which it has routinely altered as Office has evolved, creating interoperability issues for users with different versions.

The letter goes on to say that Microsoft's customers, especially in the government sector, prefer an open, standardised document format, and the letter defends the Ecma process that resulted in OpenXML standardisation.

Microsoft uses the letter to focus on the comparison of ODF and OpenMXL, saying, "It is important to recognise that ODF and Open XML were created with very different design goals and that they are only two of many document format standards in use today, each of which has characteristics that are attractive to different users in different scenarios." The letter notes that PDF and HTML also are ISO standard document formats.

Observers do acknowledge that ODF is nowhere near as feature rich as OpenXML.

"ODF from a feature standpoint is supporting a subset of OpenXML; there is a ways to go on ODF," says Chris LeTocq, principal analyst of Guernsey Research. "Even if you are IBM and you are committed to ODF you would also have to support OpenXML if that is what customers ask you to do."