I am working on a project where we need to save data in an XML format. The problem is, over time we expect the format / schema for our data to change. What we want to be able to do is to produce scripts to migrate our data across different schema versions. We distribute our product to thousands of customers so we need to be able to run / apply these scripts at customer sites (so we can't just do the conversions by hand). I think that what we are looking for is some kind of XML data migration tool. In my mind the ideal tool could:

1. Do an "XML diff" of two schema to identify added/deleted/changed nodes.

2. Allow us to specify transformation functions. So, for example, we might add a new element to our schema that is a function of the old elements. (E.g. a new element C where C = A+B, A + B are old elements).

So I think I am looking for a kind of XML diff and patch tool which can also apply transformation functions. One tool I am looking at for this is Altova's MapForce . I'm sure others here have had to deal with XML data format migration. How did you handle it?

Edit: One point of clarification. The "diff" I plan to do is on the schema or .xsd files. The actual changes will be made to particular data sets that follow a given schema. These data sets will be .xml files. So its a "diff" of the schema to help figure out what changes need to be made to data sets to migrate them from one scheme to another.