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Re: Requirements for a possible "RDF 2.0"

From: Kjetil Kjernsmo <kjetil@kjernsmo.net>
Date: Thu, 14 Jan 2010 22:43:57 +0100
To: semantic-web@w3.org
Message-id: <201001142243.57738.kjetil@kjernsmo.net>

Like some others, I think the adoption problem is not solved by another 
spec, but by actually writing useful stuff. Still, I think there are things 
that should be fixed, but relatively minor things. I'm +1 on stuff like 
graph naming, kill bag, rec on serialisations, etc, but let me also bring 
forward one little thing that is of major importance: Units.

There are no good ways to express the units of numbers in RDF. Yet, most 
numbers out there are expressed with units. You could do it with datatype 
URIs, but datatypes are orthogonal to units. You could do it with some 
hacks, people have been doing that, but it quickly gets complicated and far 
from ideal. We really need a simple way to express units, and ways to make 
it possible for agents to convert numbers between different units.

Concrete example: Lets use DBPedia to find aircrafts with a certain maximum 
take-off-weight that can take off from airfields with a certain maximum 
runway length. All the data is on Wikipedia, and writing the SPARQL query 
should be easy (actually doing it is left as an exercise to the reader ;-) 

But it can't be done, at least not without a lot of painful hacking on the 
client side, partly because not all the data is in DBPedia (notably, the 
take-off-run when the aircraft is fully loaded i.e. at MTOW), but 
importantly because of the units used, see e.g.:
where the numbers are dimensionless, and the unit is in the property, e.g.:
dbpprop:r1LengthF, while the MTOW is expressed like this:
dbpprop:maxTakeoffWeightMain	"20,200 lb"@en ;
for http://dbpedia.org/page/Cessna_Citation_Excel

So, this is actually pretty useless. You cannot do the stuff that Linked 
Data should be good at with this.

So, you could say that this could be done Right and Consistently, whatever 
Right may be, but when we, as a community (DBPedia is our community 
project, right) has failed to do it Right, I would blame it on that it is 
too hard to do Right.

Not only is this important for everyday applications, it is also 
indispensable for most scientific applications. So, that's my main 


Kjetil Kjernsmo
Received on Thursday, 14 January 2010 21:44:41 UTC

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