"Even the most humble carpenter has hammers of different sizes"
Hypothetical Problem:
An average payload of 50-100 bytes of data needs to be made available via an online service - but an enterprise canonical XSD structure might flood the network with about 200K of just empty tag elements alone.
Proposed Solution:
For certain types of data servcies, a light-weight RESTful service using JSON (over heavier-weight enterprise-level XSD-based canonical models for SOAP-based SOA services) might be more appropriate.
JSON Schema
RFC 4627 - The application/json Media Type for JavaScript Object Notation (JSON)
JSON support in JAXB
XMLSpy supports XML-to-JSON conversion
http://www.altova.com/xmlspy/json-editor.html