Determine the number of days in a False period in a Temporal Boolean

Question

Hi all,
I need to determiine the number of days based on a condition that lies on the gaps between the periods.
My input consists of multiple periods. The length of the gap is the condition to determine the start date for summation. However, there can be multimple gaps between my instances that satisfy this condition and I need the last one that satisfies it.
For example:
period 1: 1-1-1990 until 31-12-1992
period 2: 1-1-1994 until 31-12-1996
period 3: 1-1-1998 until 31-12-1999
period 4: 1-6-2000 until 31-12-2009
The condition for the start date is the last gap greater than 1 year. In this example, the start date should be the start date of period 3: 1-1-1998, because this is the period after the last gap >= 1 year. Period 2 also has a previous gap of >= 1 year, but this period should NOT be selected.
My first idea was to use a TBR function: to determine relevant periods (based on the gaps before and after), calculate the amount of days per relevant period and add those up. However, if I want to do that I need to calculate the number of days in the gaps and I don't see how to do that, since I cannot determine a day difference across periods (end date period 1 until start date period 2).
Any help/ other solution ideas?
Kind regards, Els

Answer 1

This was an interesting puzzle which you can solve from a couple of different angles.
Firstly, you can use inferred relationships to infer a relationship "the following periods" (ie. the periods that follow the current one). My rules looked like this:
the period (the other period) is a member of the following periods if
   the other period start date > the period start date
the period’s next start date = InstanceMinimum(the following periods, the period start date)From here it should be easy to see if there was a gap of more than a year, and find the most recent period after a year-long gap. Of course you need to deal with the situation of the last period, when there is no 'next' period, presumably you would use the date of assessment in that case, but I'll leave that as an exercise for the reader.
A completely different way of doing it is to use the TemporalConsecutiveDays function to find a date where a gap of 365 days exists, then select periods in which there is a gap immediately before the start of that period. Here are some rules that :
there is a period that applies if
   ExistsScope(the periods)
      TemporalOnOrAfter(the period start date) and
      TemporalOnOrBefore(the period end date)
there is a year-long gap if
   TemporalConsecutiveDays(365, 365, there is not a period that applies)
the period starts after a year-long gap if
   ValueAt(the period start date, there is a year-long gap)
the start date for calculation = InstanceMaximumIf(the periods, the period start date, the period starts after a year-long gap)Hopefully one of these is suitable for your needs.
cheers,
Steve.