With Windows Vista set for consumer release next month, millions of desktops will soon come with support for Microsoft's new XML-based XPS document exchange format built in. In an effort to preempt this move, Adobe is now testing a set of XML extensions to its own PDF document format. The new format, called "Mars," is supported by a plugin that works with existing copies of Adobe Acrobat 8 (both the professional document creation versions and the free Reader).

The Mars format consists of a single file with a .MARS extension. This file is actually a .ZIP compressed archive containing multiple files inside it. The text of the document is contained in human-readable .XML files; bitmaps are stored in the .PNG format, and scalable vector graphics are saved in Adobe's .SVG (Scalable Vector Graphics) format. Additional files in the package include metadata information, color maps, and optional file attachments.

XML is the hot buzzword in computing circles, and for a very good reason: interoperability. Unlike binary file formats, XML files are written in a readable, text-based format, and it is increasingly easy for programmers to write utilities that transfer information between XML files and other applications. It is the promise of this interoperability that convinced Microsoft to switch from their binary Office document format (.DOC, .XLS, etc.) to Office OpenXML (.DOCX, .XLSX, etc.) for Office 2007, and to make the new format the default for saving files.

Microsoft has long been trying to combat the PDF format with a document viewer standard of their own: earlier versions of Office came with a way to save files as Microsoft Document Images (.MDI), a format that never really caught on as a way to exchange documents because viewing it required the receiver to have a recent copy of Office installed. Microsoft is hoping that bundling XPS with every copy of Vista will help spur its adoption, but it is an uphill battle. PDF has become a de facto standard for document interchange, and even the most novice of computer users know about installing Acrobat Reader. Microsoft even went so far as to include PDF saving in beta versions of Office 2007, although a threatened lawsuit from Adobe convinced them to take it out of the final version—it is now available as a free download, however.

But while PDF has clearly won the document exchange format war for the present, the battle for the XML-enabled war of the future may still be up for grabs. Many people won't know what to do when presented with a .MARS file, and the number of .MARS files being exchanged will likely remain small for the immediate future. In the mean time, .XPS files are likely to become more popular as Vista slowly starts to replace XP on corporate desktops. If this happens, look for Adobe to fully integrate Mars support with all their products and push it aggressively the way the company promoted PDF in the past.

Source: http://arstechnica.com/news.ars/post/20061222-8487.html