Battle lines are forming over Microsoft Corp's support for a Sun Microsystems Inc initiative to build a standards-based set of XML-based file formats for Office applications.

The formats are based on existing technologies in OpenOffice 1.0, which is itself the basis of Sun's StarOffice 6.0. Santa Clara, California-based Sun said this week it has invited Microsoft to join the committee.

However, Simon Marks, Microsoft Office product manager, said that Microsoft would not be interested in joining if the technical committee produced "just another file format that panders to the lowest common denominator."

Marks said Microsoft is more interested in working with "customer defined" XML built using XSD 1.0, rather than interoperability between competing suites. File formats in Microsoft's up-coming Office 11 suite use XSD 1.0.

Microsoft believes "customer defined XML" to be XML schemas written to present data in specific vertical sectors, such as the financial services industry's eXtensible Business Reporting Language (XBRL). Microsoft supports XBRL in Business

Solutions Navision 3.60, launched in October.

"We didn't pick XSD to provide interoperability with other people's software. We put it in to make [Office] more relevant to the customer. It's about sharing information not documents," Marks said.

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