Alejandro, you probably need to add some template rules to your 
stylesheet to process your links.  As far as 'correct syntax' goes, that 
is open to interpretation.  Several consortia have created "Best 
Practice" guides that you might want use as a guide.  See this thread 
from the list archives for more information:

http://listserv.loc.gov/cgi-bin/wa?A2=ind0603&L=EAD&P=R325&I=-3

[log in to unmask] wrote:
> On behalf of a colleague. She is trying to link EAD instances to 
> external files (as far as I know, jpg, xml, and topic maps). She is 
> seemingly using a correct syntax, but she is not obtaining any kind of 
> result. I have been reviewing some sample and all is ok (although I 
> didn’t review stylesheets, for instance).
> 
>  
> 
> She (and I) would be grateful if she could know the correct syntax to 
> link these kind of files.
> 
>  
> 
> Thank you very much
> 
> Alejandro Delgado Gomez
>