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Re: [m2m-iwg] MQTT <-> REST+websocket mapping



2013/3/18 UOMo <uomo@xxxxxxxxxxx>
Matteo/all,

Thanks for the updates. Probably have to see what's discussed on the Paho mailing list, too.

2) I tried that URL and at first it it empty. When you click "Edit" and enter any sort of value, like 56 or 32, it keeps coming back with "18" as a result. Given the different input, I assume it isn't temperature conversion, but I would have hoped to see that "18" in the first place.

Actually that's the sensor updating the value :).
Werner, you cannot change my house temperature :).
 
And while one may guess that your home in Italy is measuring temperature in Degree Celsius, in the World Wide Internet of Things this isn't obvious at all.
A classical example of Units that must be taken into consideration. 

You are totally right.
I'm not currently addressing that point, which should be taken into consideration.

However, I believe a standard message representation for sensor data should emerge, one which includes all possible metadata to allow further consumption. That should at least support:
1) time
2) space (lat & long)
3) unit of measurements

A full discussion on all possible requirements has been done by the Semantic Web community in the SSN ontology: http://www.w3.org/2005/Incubator/ssn/wiki/Report_Work_on_the_SSN_ontology.

3)
See above, I had a few discussions with the makers of Cosm when it was still called Pachube, as their datafeeds vary a lot. Some have decent handling of measurement values and units, e.g. 

Energy, wind speed and temperature
none of them with a proper unit
A feed from Belgium: https://cosm.com/feeds/66151
says "°" but is it Celsius, Fahrenheit or Rankine?
This one has no data feed, but the temperature unit is said to be "c":
Not standard compliant, but at least gives a vague idea it seems Celsius
This air quality Egg from Portland, OR
shows "Deg C" among other units, even a bit better.
And this one from Slowenia
wins the "World Cup", not just of Alpine Skiing, by properly declaring "°C"


If any of these values shall make sense in a Global M2M environment, metadata must contain units of measurement, and a unit or code system. That could be ISO, USCustomary, Imperial, UCUM or whatever, as long as both sides can adjust to the right system to understand each other

5) Cosm uses OAuth 2.0, at least there is a Beta trial, so is for MQTT btw, although it says, it may go away with no further warning https://cosm.com/docs/beta/mqtt/

The problem with Pachube/Cosm is that is built to store data, not to let the devices talk and work between themselves in an autonomous way.

Cheers,

Matteo
 

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