1. Learning Positional Features for
Annotating Chess Games:
A Case Study
Matej Guid, Martin Mozina, Jana Krivec,
Aleksander Sadikov and Ivan Bratko
CG 2008
Faculty of Computer and Information Science
University of Ljubljana, Slovenia

2. Enhanced Knowledge in Chess Programs
 The improvements of Rybka 3 in evaluation function for chess middlegames:
 understanding good and bad bishops,
 much more advanced understanding of kings attacks,
 importance of defending king by pieces,
 “space” (previously addresed only indirectly)
(Larry Kaufmann, designer of Rybka’s evaluation function, RybkaForum.net)
How to “teach” a program to recognise chess concepts?
 Knowledge is particularly important when annotating chess games…

3. The Concept of the Bad Bishop
 Chess experts in general understand the concept of bad bishop.
 Precise formalisation of this concept is difficult.
Traditional definition (John Watson, Secrets of Modern Chess Strategy, 1999)
 A bishop that is on the same colour of squares as its own pawns is
bad:
 its mobility is restricted by its own pawns,
 it does not defend the squares in front of these pawns.
 Moreover, centralisation of these pawns is the main factor in deciding
whether the bishop is bad or not.

4. CRAFTY's Features for Describing Bishops
Feature Description Defficiency for annotating
BLACK_BISHOP_PLU
S
_PAWNS_ON_COLOR
number of own pawns that
are on same colour of square
as bishop
all such pawns count the same,
regardless of their position and
how badly they restrict the bishop
BLACK_BISHOPS
_POSITION
evaluation of bishop's posi-
tion based on predefined
values for particular squares
such predefined value is not the
actual value of bishop's placement
in a particular position
BLACK_BISHOPS
_MOBILITY
number of squares that
bishop attacks
number of attacked squares
and actual bishop's mobility
are not necessarily the same thing

5. CRAFTY's Features for Describing Bishops
Feature Description Defficiency for annotating
BLACK_BISHOP_PLU
S
_PAWNS_ON_COLOR
numbe r of own pawns
that are on s ame colour
of s quare as bis hop
all such pawns count the same,
regardless of their position and
how badly they restrict the bishop
BLACK_BISHOPS
_POSITION
evaluation of bishop's posi-
tion based on predefined
values for particular squares
such predefined value is not the
actual value of bishop's placement
in a particular position
BLACK_BISHOPS
_MOBILITY
number of squares that
bishop attacks
number of attacked squares
and actual bishop's mobility
are not necessarily the same thing

6. CRAFTY's Features for Describing Bishops
Feature Description Defficiency for annotating
BLACK_BISHOP_PLU
S
_PAWNS_ON_COLOR
number of own pawns that
are on same colour of square
as bishop
all such pawns count the same,
regardless of their position and
how badly they restrict the bishop
BLACK_BISHOPS
_POSITION
evaluation of bishop's posi-
tion based on predefined
values for particular squares
such predefined value is not the
actual value of bishop's placement
in a particular position
BLACK_BISHOPS
_MOBILITY
number of squares that
bishop attacks
number of attacked squares
and actual bishop's mobility
are not necessarily the same thing

7. Static Nature of Positional Features
 Positional features in evaluation functions are static in their nature
 Heuristic search enables to fulfil their purpose – contributing to the program
finding best moves

8. Static Nature of Positional Features
 Positional features in evaluation functions are static in their nature
 Heuristic search enables to fulfil their purpose – contributing to the program
finding best moves
 It is also desirable for positional features for annotating chess games
to be of static nature! Heuristic search is important for instructive annotations.
 see the paper Automated chess tutor. CG 2006, Turin, Italy, May 29-31, 2006.
Is freeing move e6-e5
possible or not?

9. Expert-Crafted Rules & Introducing
Learning
 Data set: 200 middlegame positions from real chess games:
 bad: 78 bishops
 not bad: 122 bishops
 We randomly selected 100 positions for learning and 100 positions for testing.
 CRAFTY’s positional feature values served as attribute values for learning.
Chess experts:
wGM Jana
Krivec
FM Matej Guid
 It is extremely difficult for chess experts to define
appropriate rules for determining bad bishops
-> knowledge acquisition bottleneck
 various expert-crafted rules performed rather poorly
(only 59% of examples were correctly classified)
-> motivation for introducing machine learning
Data Set for Machine Learning

10. Bad Bishops from Static Point of View
 Our goal: construct a static positional feature BAD_BISHOP
 Assessing bishops “statically” is counter-intuitive from chess point of view
 Special guidelines were chosen for determining “statically” bad bishops…
The bishop is bad from the static point of view in some position, if
1.
its improvement or exchange is desirable2.
the pawn structure limits the bishop’s chances for taking an active part in the
game,3.
its mobility in this position is limited or not important for the evaluation.
Guidelines for Determining Bad Bishops from Static Point of View

11. Standard Machine Learning Methods'
Performance with CRAFTY's features only
 Machine learning methods’ performance on initial dataset
Method Classification accuracy
Decision trees (C4.5) 73%
Logistic regression 70%
Rule learning (CN2) 72%
 The results were obtained on test data set.
 The results obtained with CRAFTY’s positional features only are too inaccurate
for commenting purposes…
 additional information for describing bad bishops is necessary.
 see the paper Fighting Knowledge Acquisition Bottleneck with Argument Based
Machine Learning. European Conference on Artificial Intelligence, Patras,
Greece, July 21-25, 2008. Available at: www.ailab.si/matej
Improved Method

12. First Critical Example
 Rules obtained by ABML method ABCN2 failed to classify this example as
"not bad“.
 The following question was given to the experts:
“Why is the black bishop not bad?“
 The experts used their domain knowledge:
“The black bishop is not bad, since its mobility is not seriously restricted
by the pawns of both players.”

13. Introducing new attribute into the domain
and adding argument to an example
 Experts’ explanation could not be described with current domain attributes.
 The argument
“BISHOP=“not bad” because IMPROVED_BISHOP_MOBILITY is high“
was added to the example.
 A new attribute, IMPROVED_BISHOP_MOBILITY,
was included into the domain:
 number of squares accessible to the
bishop, taking into account only own
and opponent’s pawn structure

14. Another Critical Example
 The ABML-based knowledge elicitation process can be used to induce rules
to
determine both good (i.e., not bad) and bad bishops.
 Now the following question was given to the experts:
“Why is the black bishop bad?“
 The experts used their domain knowledge:
“The black bishop is bad, since black pawns block its diagonals.”

15. Introducing new attribute into the domain
and adding argument to an example
 Experts’ explanation could not be described with current domain attributes.
 The argument
“BISHOP=“bad” because BLACK_PAWN_BLOCKS_BISHOP_DIAGONAL is high“
was added to the example.
 A new attribute,
BLACK_PAWN_BLOCKS_BISHOP_DIAGONAL,
was included into the domain:
 pawns on the color of the square of the
bishop that block the bishop's (front)
diagonals
 weights of such pawns were taken into
account (see the “Look-up table” that follows)

16.  Method failed to explain critical example with given argument.
 Counter example was presented to experts:
 Experts’ explanation: “The black bishop is not bad, since its mobility is not
seriously restricted, taking the pawn structure into account.”
Counter example: “bad”, although
BLACK_PAWN_BLOCKS_BISHOP
_DIAGONAL is high.
Counter example
 "Why is the “green” bishop not bad, compared to the “red” one?"
Critical example: “not bad”,
BLACK_PAWN_BLOCKS_BISHOP
_DIAGONAL is high.

17. Improving Arguments with Counter Examples
 The argument given to the critical example was extended to
“BISHOP=“bad” because BLACK_PAWN_BLOCKS_BISHOP_DIAGONAL is high
and IMPROVED_BISHOP_MOBILITY is low.”
 With this argument the method could not find any counter examples anymore.
 The new rule covering the critical example became:
if BAD_PAWNS_BLOCK_BISHOP_DIAGONAL > 16
and IMPROVED BISHOP MOBILITY < 4
then BAD_BISHOP= “bad” class distribution [42,0]

18. Assesing “Bad” Pawns
 Experts designed a look-up table (left) with predefined values for
pawns that are on color of square of the bishop in order to assign
weights to such pawns.
BAD_PAWNS_AHEAD = 16 + 24 + 2 = 42

19. After the Final Iteration...
Attribute Description
BAD_PAWNS
pawns on the color of the square of the bishop -
weighted according to their squares (bad pawns)
BAD_PAWNS_AHEAD bad pawns ahead of the bishop
BAD_PAWNS
_BLOCK_BISHOP_DIAGONAL
bad pawns that block the bishop's (front) diagonals
BLOCKED_BAD_PAWNS bad pawns blocked by opponent's pawns or pieces
IMPROVED_BISHOP_MOBILITY
number of squares accessible to the bishop taking
into account only pawns of both opponents
 The whole process consisted of 8 iterations.
 7 arguments were attached to automatically selected critical examples
 5 new attributes were included into the domain

20. Classification Accuracy Through Iterations
 The accuracies of all methods improved by adding new attributes.
 ABCN2 (which also used the arguments) outperformed all others.
Arguments suggested useful attributes AND lead to more accurate models.

21. The Final Model
 Rule #2:
if BAD_PAWNS_AHEAD > 18
and IMPROVED_BISHOP_MOBILITY < 3
then BISHOP= “bad” class distribution [46,0]

22. The Final Model
 Possible comment:
“Black bishop is bad,
since black pawns on the same colour of squares ahead of it,
and pawns of both opponents restrict its mobility.”

23. Conclusions
 In this case study, Argument Based Machine Learning was shown to be
a powerful knowledge-elicitation method for defining deep positional
patterns.
 ABML offers the following advantages for knowledge elicitation:
explain single example easier for experts to articulate knowledge
critical examples expert provides only relevant knowledge
arguments constrain
learning
hypotheses are consistent with expert
knowledge