Author: David Eppstein
Date: 23:00:13 11/05/99
CCC readers may be interested in the article "Knowledge Discovery in Deep Blue",
by Murray Campbell, in the latest Communications of the ACM. For ACM digital
library subscribers, it can be found at
http://www.acm.org/pubs/citations/journals/cacm/1999-42-11/p65-campbell/
Anyway, it's about how DB plays in the opening phase of the game. According to
Campbell, the actual book (by which he seems to mean, an explicit move tree
generated by a human) is "only a few thousand positions". Apparently, though,
it also has a database of millions of grandmaster game positions -- if the
program reaches a position in this database but out of book, it does a search in
which database information is used to award bonuses to certain moves. The basis
for awarding these bonuses is apparently a complicated ("nonlinear") function of
features such as game outcome, relative and absolute numbers of times the move
has been played, how recently it was played, etc.
The example he uses is DB-Kasparov rematch game #2 (the Ruy Lopez that Kasparov
resigned even though he could have forced perpetual check). According to
Campbell, the first nine moves were in book. Moves 10-17 were not in book, but
the database bonus was so large that it just made the move without searching.
Finally, on moves 18 and 19, it made a search in which the moves that ended up
being made (18 Qd2 and 19 a4) were given bonuses of 17 and 9 centipawns
respectively. After move 19, the game went over new ground and this database
machinery stopped being useful.
He also mentions the second game of the first match, in which the explicit book
was apparently disabled, but the database extension to the book still worked,
and allowed the program to follow theory for 13 moves, reaching (he claims) "a
respectable opening position" although the game was later lost.
The paper is only three pages long, though, so if you're looking for technical
detail it won't be there.
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