It may be Valentine's Day but there are no love letters being exchanged between duelling electronic document formats, ODF (OpenDocument Format) and Open XML. Instead, Microsoft, the backer of Open XML, took a public swing at ODF supporter IBM.

Microsoft posted an open letter on its Web site Wednesday titled "Interoperability, Choice, and Open XML," signed by two of its general managers -- Tom Robertson, who handles interoperability and standards, and Jean Paoli, responsible for interoperability and XML architecture.

In the letter, Microsoft claimed that IBM is attempting to slow down the approval process by the International Organization for Standardization (ISO) to recognize Open XML as an international standard.

IBM declined to comment publicly on the letter, but a spokesman said the company had previously addressed many of the issues raised by Microsoft.

In May, ISO approved ODF as an international standard and is currently considering whether to award the same recognition to Open XML.

ODF has the backing of such companies as IBM, Google, Novell, Sun, and open-source players. Open XML is the default file format for Microsoft's Office 2007 desktop applications suite. What has yet to become clear is which document format users will favor -- ODF or Open XML -- or whether they'd adopt a mix of the two. Some vendors, such as Corel, have already announced they're adopting a neutral approach and will support both formats in their software.

IT users and governments around the world are expressing interest in open-standard document formats to help ensure continued access to archived information and also free them from having to use Microsoft's Office software.

In December, standards body ECMA International voted 20 to 1 to approve Open XML as a global standard and submitted the format to ISO for its approval. The dissenting vote came from IBM, according to Microsoft.

"IBM has declared victory in blocking Open XML," the Microsoft letter alleges, claiming that IBM is holding up the standards process in a "blatant attempt" to limit choice in the marketplace designed to favor the vendor's Lotus Notes groupware, which doesn't support Open XML. Microsoft and IBM are the two leading desktop collaboration software vendors with IBM's Notes pitted against Microsoft's Outlook and Exchange software.

Microsoft is fearful that ODF may become the de facto electronic document format by default simply because it was first to achieve ISO recognition as an international standard, the letter stated.

"In XML-based file formats, which can easily interoperate through translators and be implemented side by side in productivity software, this exclusivity makes no sense -- except to those who lack confidence in their ability to compete in the marketplace on the technical merits of their alternative standard," the letter continued. "This campaign to limit choice and force their single standard on consumers should be resisted."

The timing of the release of Microsoft's letter is interesting given that it comes a day after the Oasis standards body announced its approval of a new version of the ODF standard, OpenDocument 1.1. The changes in ODF 1.1 are designed to address concerns voiced by advocacy groups that the previous release didn't meet the needs of people with disabilities. The level of accessibility support provided in ODF 1.1 is now on a par or exceeds that available in other file formats.