Since XNAT's data structure is XML-based, users can easily upload and download XNAT data in XML format from anywhere in the application. However, when uploading new XML definitions, there are a few caveats to be aware of.
Users with appropriate permissions can upload XML definition documents from anywhere in the XNAT UI by clicking on Upload > XML in the top navigation. This brings up a simple UI with just a few controls that allows users to select and upload a single XML file.
If the "Allow Data Deletion" parameter is set to true, then any XML definition you upload will overwrite any existing record with the same accession ID.
The XML Uploader uses XNAT's StoreXML service to parse your XML document and create or modify records in your XNAT database. XML definitions can be uploaded for projects, subjects, or any subject assessor.
XNAT administrators can download XNAT Client Tools that include a version of StoreXML. This will allow you to script an upload of multiple records at once. See: XNAT Web Services Client Tools.