Mandatory and additional properties for _TimeSeries

Created by: JoachimBenner

For the processing of time series (_TimeSeries), it is essential to know how the different values need to be interpreted, e.g. whether they represent the total amount of a measure value or a single value, whether the measure values are related with the preceeding or the succeding time interval, and whether it is feasible to interpolate between different values. This indispensible information can be stated with the property interpolationType of TimeValuesProperties, with actually is optional but should be mandatory.

In several use cases, the time series will be generated by "meters" (e.g. electricity or gas meters), and the values of the time series represent a "total amount" (InterpolationType InstantaneousTotal, PreceedingTotal or SucceedingTotal). The meters normally have a value different from zero at the starting time of the time series, and this starting value must be known to interpret the time series values.

Proposal

1. Make property variableProperties of _TimeSeries mandatory
2. Make property interpolationType" of *TimeValuesProperties mandatory
3. Add optional property startValue (type Measure) to TimeValuesProperties