units and durations

Hi all,

I've got a question regarding standards to represent certain units and
durations with typed literals. We try to use standard data formats (such
as xsd:date) in DBpedia, and defined our own ones (such as
<http://dbpedia.org/ontology/kilometre>) if we couldn't find any
standards. 

1. lengths: 
metre, kilometre, centimetre, km^2, etc.
dbpedia:Rhine <http://dbpedia.org/ontology/length>
"1320"^^<http://dbpedia.org/ontology/kilometre>

2. runtimes
seconds, minutes, hours, days...
dbpedia:Yellow_Submarine_(song) <http://dbpedia.org/ontology/runtime>
"2:38"^^<http://dbpedia.org/ontology/minute>
dbpedia:The_Departed <http://dbpedia.org/ontology/runtime>
"151"^^<http://dbpedia.org/ontology/minute>

3. durations
dbpedia:Thirty_Years'_War <http://dbpedia.org/ontology/date>
"1618-1648"^^???


Any pointers to standard data formats for those?

Thanks,
Georgi

--
Georgi Kobilarov
Freie Universität Berlin
www.georgikobilarov.com