xlink:href

Hi all, i've problems to determine the right path for a internal resource with
xlink's attribute, href.

i found this different ways suggested:

<mets:FLocat xmlns:xlink="http://www.w3.org/1999/xlink" LOCTYPE="URL"
xlink:href="file://Scan00001.tif"/>

this second one:

<mets:FLocat xmlns:xlink="http://www.w3.org/1999/xlink" LOCTYPE="URL"
xlink:href="file:///Scan00001.tif"/>

(with 3 slash... i don't understand the difference)

and the last:

<mets:FLocat xmlns:xlink="http://www.w3.org/1999/xlink" LOCTYPE="URL"
xlink:href="Scan00001.tif"/>

when can i use these ways? are there differences?
thanks to all.