Doing business with documents implies an agreement about what the documents mean and about how the recipient will process and reply them – we need formal (and computer readable) models for both the documents and the processes in which they participate
Businesses try to differentiate themselves but tend to do things in similar ways – and the fundamental requirement for "mutual intelligibility" leads to regular patterns in documents and business processes
There is always tension between the optimal document designs for a business's internal processes and the need for those documents to be understood by other businesses. This induces document designers to reuse existing models wherever possible and reinforces them if they describe any new models they create in ways that encourage their reuse by others.
Using XML schemas to encode the models of both the documents and their associated processes is attractive for both theoretical and practical reasons