In the Form Builder tool from Orbeon it's possible to specify a schema by uploading a XSD file.
But if we don't have the schema or we are too lazy to c reate it, is it possible to create dynamically the schema ?
The schema is needed for the use of the form datas in other systems like a Business Object universe.
Regards
Orbeon Forms doesn't automatically generate schemas based on the forms you create in Form Builder; instead, as you noted, it is designed to consume a schema that you already have.
However, there are tools that do just that. You can find some mentioned on the answer to this question on how to generate an XSD schema from an XML instance document.