We have a number of workbooks that contain a lot of data. Each workbook has
been separated into multiple identically-formatted worksheets based on
geographical divisions (up to 16 separate worksheets in a workbook).

Until now we have been saving the data in "XML Spreadsheet" format. Each new
version is checked into source control without merging because the internal
formatting of the workbook causes major merge problems.

I am trying to save the workbooks as XML Data so that source control could
save only the differences between versions. I have been successful at
defining a schema to save a single worksheet. But as soon as a sequence or
choice is added to allow mapping for a second worksheet I get the message
that the XML maps cannot be exported. Also, if the schema reuses a complex
element to describe the data row, Excel won't let the atomic elements to be
mapped more than once.

After many different schema designs, I'm wondering if it is simply not
possible. Does anyone have suggestions about how to approach this problem?

In the end, I would like a single XML document for each workbook containing
the data from all of its worksheets, using the same element names for each
worksheet.