On 07/10/16 11:32, Claude Warren wrote:
So I guess the question is if you want to know say the temp recorded across multiple devices at a specific time how hard is it to query.
Easy, find all observations about that time, don't filter on device.
or if you have devices that quantize time (say 10 minute intervals) and someone asks for data at a 15 minute interval can you retrieve the data as reported at the earlier 10 min interval (eg. data recorded at 01:10 when 01:15 time is requested)
We maintain a "latestValue" link so finding the latest value for each measurement station is easy. Finding values in a time window is just a SPARQL range filter. Finding the last reading before some arbitrary time is harder. I would do a range query wide enough to have at least one measurement, but not too many, then filter for latest measurement which is =< the target time.
Dave
