Microsoft has released the first finished version of the software development kit (SDK) for the Open XML Format, the default storage format for Microsoft Office 2007 and the basis for a standard that is currently awaiting publication by the International Organisation for Standardisation (ISO).

Open XML SDK 1.0 , available from the company's website, is designed to allow developers to produce code enabling their applications to create, access and manipulate Open XML documents, Microsoft said.

The SDK includes an application programming interface (API) simplifying the creation of code for searching documents, creating documents, validating document parts, modifying data and other tasks, Microsoft said.

The API can be used in any language supported by the Microsoft .Net Framework, the company said.

A pre-release version for version 2.0 is scheduled for late summer, with the final version intended for release along with the next version of Office, code-named Office 14.

The current SDK supports the version of Open XML supported by Office 2007, which is not the same as that ratified as a standard by the ISO, due to changes effected during the ratification process.

That standard, called IS29500, was approved by the ISO in March, and Microsoft has said that it will update the support for Open XML to be in line with the standardized version in Office 14.

At the same time, Microsoft said last month that it will begin supporting the rival Open Document Format (ODF) in Office 2007 and Office 14, beginning with a service pack set for release in the first half of 2009.

Microsoft acknowledged in May that it was adding support for ODF partly because of the difficulty involved in modifying Office to support the standardized version of Open XML.

"The ISO/IEC standardization process resulted in a number of changes to the Open XML specification," the company said in a statement. "While developing our support for ODF requires a substantial amount of work, changes to existing file formats are often more complex than developing new code and therefore more difficult to implement due to backwards compatibility considerations."

Several ISO member countries are currently appealing against the decision to fast-track Open XML standardization, which has delayed the publication of the standard while the appeal is resolved.

Opponents of the format have said that it is needlessly complex, comprising 6,000 pages of documentation, and that documentation is unclear.