You might be thinking of a Zettelkasten.

You could read Manfred Kuehn's discussion of Zettelkastens at

http://takingnotenow.blogspot.co.uk/2007/12/luhmanns-zettelkasten.html

or Dr. Kuehn's translation of Niklas Luhmann essay (Luhmann is credited as the "inventor" of the Zettlekasten technique)

http://scriptogr.am/kuehnm/post/title-communicating-with

or browse Christian Tietze's blog on the topic of Zettelkastens

http://zettelkasten.de

or experiment with Daniel Luedekke's Zkn3 software

http://zettelkasten.danielluedecke.de/en/index.php

PS - there was a German filing system mentioned here a while back,

where each note is tagged with an ID number?...
I don’t remember the name. Wondering if this would help?