An XSD document defines the data schema handled by a service provider. It can be created in a choreography diagram with any orchestration languages.
When you reverse engineer or import web services, provided you have selected the Create XML Model option, an XSD document is created for each data schema found in the source WSDL. This XSD document is displayed in the XSD Documents tab of the service provider property sheet.
An XSD document can be associated with an XML model in order to provide a graphical representation of the service provider data schema (see Attaching an XML model to an XSD document).
An XSD document belongs to a service provider.