Hello,
at this moment there is no explicit meta-model of the projects developed with WebRatio.
The XML files that represent a WebRatio project (Model.wr and all the files included in the Model folder) are validated directly in Java by WebRatio itself. There is not a XSD or ECore file describing the metamodel.
You can try to "rebuild" the metamodel by downloading a project from the WebRatio Store and inspecting the XML available in files \ folders mentioned above.
Regards,