Sorry, I don't understand your question.
To store content (such as XML), you can use the ContentService api to read and write. If you want it versioned, add the VersionableAspect to the content node that represents the xml file. If you want the xml content node to be associated with the person, you can add it as a child of the person, or associate it with the person (via the NodeService). I believe there's already a child configuration folder under each person, so you could place the xml content node in there.
Like all content managed in Alfresco, it's stored in the file system - only content meta-data is stored in the database.
That might help.