Time shifts from UTC

[rybesh]

EDTF Level 0 supports the concept of “time shifts” in hours or in hours and minutes with respect to UTC. The examples from the spec are:

[dateI][“T”][time][shiftHour]
Date and time with timeshift in hours (only)
Example 3       ‘1985-04-12T23:20:30-04’ refers to the date 1985 April 12th time of day 23:20:30 with time shift of 4 hours behind UTC.

[dateI][“T”][time][shiftHourMinute]
Date and time with timeshift in hours and minutes 
Example 4       ‘1985-04-12T23:20:30+04:30’ refers to the date 1985 April 12th,  time of day  23:20:30 with time shift of 4 hours and 30 minutes ahead of UTC. 

I find the explanation a bit confusing as it unclear whether the datetime refers to the UTC time or the local time. Since there is no Z, I’m assuming that it refers to local time.

So, under that interpretation, 1985-04-12T23:20:30-04 means 11:20:30PM on 12 April 1985 in the UTC−04:00 time zone, which would be the same as 3:20:30AM on 13 April 1985 UTC time.

I propose to model time shifts as instances of time:ProperInterval where one endpoint of the interval is the UTC time and the other endpoint is the shifted local time (i.e. the time being described by the EDTF expression). The duration of the shift is described using time:hasDurationDescription.

So in the example given above, the shift is an interval beginning at 11:20:30PM on 12 April 1985 UTC time and ending four hours later at the time described by the EDTF expression (which would be 3:20:30AM on 13 April 1985 UTC time, though this is not explicitly stated by the proposed modeling). See level-0/datetime-shifthour.ttl.

When the shift is positive rather than negative, the interval begins at the time described by the EDTF expression and ends at a specific UTC time. See level-0/datetime-shifthourminute.ttl.