Microsoft XPS - is this just a 'not invented here' development?

I have to admit that I know little about Microsoft's XML Paper Specification (XPS). Based on my research for yesterday's post about MS Office document intelligence I see that XPS is intended to be able to provide Microsoft products with device independent, repeatable rendition for viewing or printing, much like PDF/A. This means you get to see how a document would look printed, every time you view it, something a little alien to MS Office to date. Darren Strange added a quick comment to my post asking what I think of XPS, and as the response grew I realized that I should make a post out of it to really demonstrate my thoughts (based on ignorance) in this area - so Darren, this is for you! (thanks for the trigger to write something).

So far I have found it difficult to find a succinct description of what XPS is, or why it is needed. Wikipedia describes XPS like this:

The XML Paper Specification (XPS) ...is Microsoft's initiative to integrate document creation and viewing into its Windows operating system. ... Most notably, XPS uses the Windows Presentation Foundation, so that the methods used for rendering for display in Windows are the same as those used for rendering for print devices.

XPS is viewed as a potential competitor to Adobe's portable document format (PDF). XPS, however, is a static document format that does not include dynamic capabilities similar to those of PDF.

Maybe anyone (Darren?) could comment on how true this description is?

If XPS really is just a static document format, I think I would struggle with the concept, though maybe there is value in something completely static for archiving. It seems that Office 2007 still has the issue that there is is no way to produce document files that are viewable/printable identically in a device independent manner, so as an addition XPS document format maybe fills the repeatable rendition gap that Office has always suffered from.

As I understand it, the XPS print rendition is not a standard part of an Office 2007 file package, making Office files poor for archiving in their original form, since they can't be guaranteed to be viewed as originally intended. At the same time, XPS lack the dynamic capabilities of PDF (presumably dynamic attributes) to be fully standalone for review and approval leading to eventual archiving.

Does Office 2007 actually insert XPS into the Office Open XML package when you 'publish' the document? That would fill the gap, since by placing a print rendition inside the Office document, an XPS enabled viewer (or even the Word editor) could show a true 'print view'. This would just need mechanisms to ensure that the versions of Office and XPS documents where aligned, so that you know that the dynamic Office document has not been changed since the last XPS was generated.

Taking the discussion back a little, maybe I'm missing the point, but why not just adopt the ISO standard PDF/A specification (based on PDF 1.4 and therefore XML based), rather than recreating yet another format to be supported by vendors? XPS needs more bloated print drivers and new viewers to be useful. What are these going to add to users and developers toolkits that help the desktop environment move forward leaps and bounds? Right now it just looks like Microsoft play the 'not invented here' card to print/display rendition documents.

I can feel the appeal of a pure XML based format for printable documents (maybe just because its XML), but why not go for Office Open XML content combined with XSL-FO, the standard XML translation specification that allows output to a range of current print formats (including Postscript and PDF)? Maybe it is the standalone XML-ness of XPS that appeals.

There must be a need here that the Microsoft XPS introduction page does not explain, since it gets bogged down early in technical capabilities and requirements. I'd love to know what that need is!

[UPDATE:
David Perry on the Freeform Comment blog has also picked up on the XPS/PDF thinking, relating it to Adobe's financial situation. He also refers back to the issues that Adobe has with Microsoft producing PDFs in Office 2007. Maybe one to watch again! ]

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