Axapta/DynamicsAx: Manual UTC datetime conversion

BuschnicK

We are trying to interpret the data stored in Axapta's TIMEZONESRULESDATA table. Particularly, we'd like to figure out how it stores DST begin/end times. So far, my guess is:

TZENUM: foreign key referencing TIMEZONESLIST (time zone name and identifier)
YEAR: 0 if rule is valid indefinitely or a year where the timezone rule is in effect
BIAS: offset to UTC time in minutes
DBIAS: offset of DST (added to BIAS to get total offset from UTC)

Now for the part I don't understand:

DYEAR,DMONTH,DDAYOFWEEK,DDAY,DHOUR,DMINUTE,DSECOND
SYEAR,SMONTH,SDAYOFWEEK,SDAY,SHOUR,SMINUTE,SSECOND

I would guess from the dates that the D* is the start date of DST and S* is end. However, I do not understand why it would need a year and a dayofweek field. Also, *DAY does not seem to indicate the day of month - at least it doesn't indicate the correct one for switching DST. It also doesn't seem to correspond to the dates at which Axapta's own DateTimeUtil or Form autoconversion converts the dates.

Does anyone know how to interprete this table? Or where I could look it up?

cheers,

Sören