When you need to use the same source multiple times in the same profile, you can give it a name and thereafter just reference the name. So for example, for the first reference, it would be something like this: <ref name='name'>source citation</ref>. Then when you need to reference it again, you use the name <ref name='name'/> instead of the full source twice. The name can be anything you want, it must be unique, contain letters, and is case sensitive.
I hope this helps.