Re: Finding overlapping time periods - suggestions please

> babette.turnerunderwood_at_hrdc-drhc.gc.ca wrote:
>
> I was wondering if anyone had the need to find overlapping time
> periods and how to identify them efficiently.
>
> Here is the scenario:
>
> Elapsed minutes refer to the actual "clock" time either
> spent on a given task. Thus an activity that started at
> 9:00 am and finished at 11:00 am on the same day is said to
> have 120 elapsed minutes.
>
> If one task overlaps another (either completely or partially
> with another task), then the tasks are said to be
> "multitasked". In that case the system will store the
> portion of the elapsed time that was multitasked as "elapsed
> multitask minutes" and the portion of the time that was not
> overlapped as "elapsed single minutes". In addition, for
> the portion of time that two or more activities were
> simultaneously taking place; their time will be divided by
> the number of simultaneous activities and stored as
> "prorated multi minutes". The sum of Elapsed Single Minutes
> and Prorated Minutes will equal the actual clock time that a
> vehicle was active.
>
> The following example should help to illustrate these
> concepts. In the table below a list of fictitious
> activities for a vehicle are shown in addition to how the
> time is allocated to the various measures:
>
> Activity Start Time End Time Elapsed Minutes
> Elapsed Multitask Minutes Elapsed Single Minutes Prorated Multi
> Minutes Prorated Minutes
> 1 10:00 12:00 120 60 60 25 85
> 3 11:00 13:00 120 120 0 55 55
> 4 11:30 13:30 120 90 30 40 70
> 7 13:30 16:00 150 0 150 0 150
> Totals 510 270 240 120 360
> The vehicle was active from 10:00 to 16:00, a total of 6 hours (360
> minutes) which is equal to the total of Prorated Minutes.
>
> The vehicle performed 8 ½ hours (510 minutes) of work during
> that 6-hour time span. This can be arrived at by adding the
> total of Elapsed Multitask Minutes (270) + the total of
> Elapsed Single Minutes (240).

Babette,

   I see the problem as quite similar to the 'let's fill up the calendar' problem. Basically the problem is to have time slices and to know what is going on during those slices.

It's pretty easy to build up a view returning one row per minute in the timespan which matters; I am using all_tab_columns as a table with more rows than I need, a smarter solution would be the infinite_dual once suggested by Tim Goraman :

  select y.t0 + rn / 1440 current_time
  from (select rownum rn

        from all_tab_columns
        where rownum < (select (max(end_time) - min(start_time)) * 1440
                        from activities)) x,
       (select min(start_time) t0
        from activities) y

If ACTIVITIES (which I supposed to be made of ACTIVITY, START_TIME, END_TIME) is indexed on both START_TIME and END_TIME, it should be fast enough.

>From there, it is easy enough to build up a kind of 'bitmap' of
activities - this for instance shows a '1' when a given task is active, '0' when it is not :

select b.current_time,

       a.activity,
       decode(sign(b.current_time - a.start_time),
                   -1, 0,
                       decode(sign(a.end_time - b.current_time), 1, 1,
0))
               active
from activities a,
     (select y.t0 + rn / 1440 current_time
      from (select rownum rn
            from all_tab_columns
            where rownum <= (select (max(end_time)
                                      - min(start_time)) * 1440
                             from activities)) x,
            (select min(start_time) t0
             from activities) y) b

a SUM() and a GROUP BY on the current time tell you how many tasks are concurrently active at a given time, etc. Should be enough to get you started ...

-- 
Regards,

Stephane Faroult
Oriole Software
-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Stephane Faroult
  INET: sfaroult_at_oriole.com

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