xetra is an electronic tradingsystem. i guess in germany every stock is traded through xetra. it is where the volume is. there are also several regional exchanges and there is also floor trading ("frankfurt").
Thanks! Europe is confusing to a newbie. I looked up DCX on Yahoo and found it traded on about 10 exchanges and struggled to find even the smallest bit of information about any of them. International equity investing has some definite obstacles to overcome...