Standard XSD and Ports

Hi Experts,

we are implementing SRM-MDM Catalog, I need to add new fields in my xml file which is coming to MDM System. So I need to edit the corresponding XSD file also. But In My console i have few xsd files, but i am not able to download and edit.

Where can i get this standard .XSD files, if any links or SAP Notes or SMP Paths, please do let me know..

You help will be rewarded in points

Thanks

Bharat