[Computer-go] Japanese byoyomi in SGF files (possible KGS Bug?)

Erik van der Werf erikvanderwerf at gmail.com
Mon Jul 29 02:27:01 PDT 2013

Well, I wouldn't go so far as to call it a bug in sgf, more something that
just needs a better description. It is unclear what exactly 'after the move
was made' means. Perhaps it should state something like 'directly after the
move was made, before making any further adjustments to prepare for the
next move (e.g., when in Japanese byoyomi)'

I don't think there's a problem with overloading the meaning of OB/OW to
handle both Japanese periods left and Canadian moves left. The OT property
allows us to distinguish the two.

My main concern is with the BL/WL property (not OB/OW), which for the KGS
implementation of Japanese byoyomi does not provide the amount of time that
was used to think about the move.

One possible way to fix this would be to use both BL and WL in every node
so that for every move you can provide information about the time both
before and after the move is made. But if one prefers to store only
information of one side (as KGS currently does), i.e. pairing BL only with
B and WL only with W, then I would say that for Japanese byoyomi the time
left shown should be the one at the end of the move before resetting the
time for the next move. The time left after resetting is redundant anyway
because the OT property already tells us the length of each period (and
the OB/OW property tells use when we are in byoyomi).


On Mon, Jul 29, 2013 at 3:50 AM, Chaz G. <chaz.gwenapp at gmail.com> wrote:

> Hi Erik,
> I would have expected "BL[2]OB[0]" more than "BL[2]OB[3]". Ultimately,
> it's a bug in sgf, not KGS.
> I think that BL (WL) and OB (OW) were documented with Canadian byo-yomi in
> mind, where BL[120]OB[3] meant that Black has 120 seconds to play 3 stones.
> The length, format, and number of Byo-yomi periods in a game should be
> tagged under OT. With Japanese byo-yomi, the literal interpretation of sgf
> properties would store BL[timeremaining]OB[0]WL[timeremaining]OW[0] for all
> periods of byo-yomi play. Using OB(OW) to mark the number of byo-yomi
> periods left is not the documented interpretation of sgf files but allows
> for a more plausible recreation of the game.
> Best,
> -Chaz
> On Sun, Jul 28, 2013 at 8:42 AM, Erik van der Werf <
> erikvanderwerf at gmail.com> wrote:
>> Hi All,
>> I was just looking at how Japanese byoyomi time information is stored in
>> sgf files. The spec at http://www.red-bean.com/sgf/properties.html tells
>> us:
>> Property: BL (WL)
>> Function: Time left for black (white), after the move was made.
>> Value is given in seconds.
>> Property: OB (OW)
>> Function: Number of black (white) moves left (after the move of this
>> node was
>>  played) to play in this byo-yomi period.
>> Now let's say we're playing in Japanese byoyomi, e.g., with 3 periods of
>> each 12 seconds. It's our turn, we think for 10 seconds and then make a
>> move. In this case I would have expected the game record to show that we
>> thought about it for 10s (2s left) using the BL/WL property. I.e. I would
>> have expected "BL[2]OB[3]"
>> However, this is not what's happening when I look at some sgf files I got
>> from KGS. What happens there is that after the move is made the clock
>> resets to 12 seconds (the time available for the next move), and that value
>> is stored in the sgf. So, once in Japanese byoyomi the sgf just shows a
>> long list of "BL[12]OB[3]", which in my opinion is not very informative
>> (all it tells us is that the move was completed within the period, but not
>> exactly how much time it took).
>> I'm tempted to think that this is a bug, but since it might also be a
>> difference of interpretation of the spec I'd like to hear what others
>> believe is the correct implementation.
>> Best,
>> Erik
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