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Pack chess_db -- prolog/chess_db.pl
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This library produces chess games databases from PGN files and provides some
predicates for manipulating these databases.

Once connected to a number of chess_db databases, information about the games
can be interrogated. (See chess_db_opening/2 for an example.)

Ideally we want to hook this pack to either a web-based interface, or (b) have an engive interface to exploit GUI playing programs, for playing the games as we select them.
Currently selected games can be saved to a PGN file and be displayed with any PGN displaying program.


?- pack_install(chess_db).

There are three example pgns in pack(chess_db/data/pgn) and an example program in pack(chess_db/examples/short.pl).

The best way to view the documentation is via the SWI-Prolog html documentation server:

?- doc_server(3004).
% Started server at http://localhost:3004/pldoc/

?- use_module(library(chess_db)).

?- www_open_url('http://localhost:3004/pldoc' )
% Which will open a browser pointing to the doc server. At this page search for the term: chess_db.

Static docs version is available at: https://stoics.org.uk/~nicos/sware/chess_db/doc/html/chess_db.html

Home page: https://stoics.org.uk/~nicos/sware/chess_db

The source code for the pack is available at github: https://github.com/nicos-angelopoulos/chess_db




The pack includes code to:

PGN's: pgn/2
the parsed terms into prosqlite databases: chess_db/2
with the resulting databases: chess_db_game_info/3, chess_db_opening_pgn/2
representation of chess games: chess_dict_start_board/1, chess_dict_move/3
representation of game positions: chess_dict_inpo/2
for identifying pinned pieces (used in move disambiguation)

See below for details on each.

A number of chess databases can be connected at the same time. Operations are implicit to all open databases. Connecting is via chess_db_connect/2.


?- [pack('chess_db/examples/short.pl')].
?- short.      % creates a chess_db in subdirectory short/ from data/4ncl_short.pgn
               % and displays the game ids for games that start with [e4,e6] (French defence)

?- french.     % creates a new pgn file from the base for the 2 games in short/ that start with e4,e6
% Using existing chess_db directory: /home/nicos/short
% (short) Following games start with 1.e4,e6
% (short) Writing 1.e4,e6 starting games to: 'short/french.pgn'
% Closing chess db: '/home/nicos/short'

% open file short/french.pgn on program that can play the games eg
linux> chessx short/french.pgn

Mini tutorial

The above example in detail.

Turn debugging of writing out the original games as they are added to the database.

?- debug(chess_db(original)).

Create a database in fresh directory short/. The DB will be populated with games from pgn file chess_db/data/4ncl_short.pgn
The database is closed after it is populated.

?- chess_db( pgn('4ncl_short'), short, create(true) ).
1. e4 e6 2. d4 d5 3. Nd2 Be7 4. Bd3 c5 5. dxc5 Nf6 6. Qe2 O-O 7. Ngf3 a5 8. O-O
Na6 9. e5 Nd7 10. Nb3 Ndxc5 11. Bb5 Bd7 12. Bxd7 Qxd7 13. Nbd4 Ne4 14. Be3 f5
15. Qb5 Qxb5 16. Nxb5 Rfc8 17. c3 Nac5 18. Nfd4 Ra6 19. f3 Ng5 20. Rad1 Nf7 21.
f4 Ne4 1/2-1/2


Connect to the new database. The connections are managed internally.

?- chess_db_connect( short, profile(false) ).

Interrogate all connected databases for games starting with the sequence [e4,e6] (French defence).

?- findall( Gid, (chess_db_opening([e4,e6],Gid),write(Gid),nl), Gids ).
Gids = [chdbs(<sqlite>(0x276c930), <sqlite>(0x278f320), <sqlite>(0x2792450)):1, chdbs(<sqlite>(0x276c930), <sqlite>(0x278f320), <sqlite>(0x2792450)):31].

Turn general library debugging on.

?- debug(chess_db(info)).

Re-connecting is handled fine.

?- chess_db_connect( short, profile(false) ).
% Handles already exist, for chess_db directory: '/home/nicos/short'

Create a new PGN file from the original scripts of the two French defence 2 games in their original script. Moves are matched to game_move/4 and are pulled from the game_orig/2 sub-database.

?- PgnF = 'short/french.pgn', chess_db_opening_pgn( [e4,e6], PgnF ).

View the two games in a PGN interface program such as:

?- shell( 'chessx short/french.pgn' ).

Find continuations for specific positions

?- chess_db_connect( short, profile(false) ).
?- chess_db_position( [e4,e6], Handles, Conts ).
Handles = chdbs(<sqlite>(0xaaaae1482af0), <sqlite>(0xaaaae1487890), <sqlite>(0xaaaae148c740), <sqlite>(0xaaaae1491500)),
Conts = '1-3-d3;31-3-d4' ;

Please note that this is more generic than chess_db_opening/2 as it also finds transpositions.

Debug terms

Listens to:

trigger light reporting across the library
(on-by-default channel, turn off for silent operation)


Portable Game Notation is the standard for recording chess games. Each file, typically with a .pgn extension, may contain multiple games. In most cases a single PGN file will contain all the games a particular chess tournament.

For example the file pack(chess_db('data/pgn/4NCL-2017.pgn') records some of the games for the 2017, 4NCL league taking place in the UK.

This pack implements a parser for PGNs (pgn/2) that converts the games in the .pgn file to a Prolog terms list, where each game is represented by a pgn(Info,Moves,Res,Orig) term (see pgn/2).

The following two queries are equivalent

?- pgn( pack(chess_db/data/pgn/'4NCL-2017.pgn'), Pgn ).
Pgn = [pgn(['Event'-'4NCL Division 1a',...]),...]

?- pgn( pgn('4NCL-2017.pgn'), Pgn ).
Pgn = [pgn(['Event'-'4NCL Division 1a',...]),...]

To disambiguate between multiple pieces that maybe able to be refered to by a game move, the pack implements a pinned piece logic. The non-interface predicate implementing this is: chess_dict_move_pin/3.

Disambiguation is needed in the following example. On a board with white rooks on b2 and b7 a move noded by Rb3, could refer to either of the rooks moving to this square. If both rooks are unconstrained the move should have be recordes as either R2b3 or R7b3. If the move is recorded as Rb3, it means that either of the two rooks is constrained by a pin: ie moving the rook would put the white king under attack. For instance, if the white king is at a1 and the black queen is on c3, then the rook on b2 is pinned and moving it to b3 whould be an illegal move. Thus, in this context Rb3 refers to moving the rook on b7 to b3.


By default, each chess_db database directory contains 4 SQLite DBs each holding a single table. In the following, a + sign prefixes a key field:

contains game_info(+Gid,+Key,Val) info Key->Val pairs about each game
table is, game_move(+Gid,+Ply,Hmv,Move)
  • Gid is the game id
  • Ply is the ply move for Move
  • Hmv is the half moves since last take (0 if Move is a take, or in start board)
  • Move is the original, algebraic, form of the move)
table is game_orig(+Gid,Orig); where Orig is the verbatim of the section in the PGN for that game
table is game_posi(Posi,GPPairs), where GPPairs is a ; seperated Gid-Ply-Move pairs stored as text (eg '1-2-e4;2-4-e3'), Posi is a long integer stored as a string
table is game_posi(Posi,Conts); where Posi is a unique position and Conts is the continuations string (Gid-Ply-Mov, eg: 1-3-d5).

Positions are encoded as long integers.

A number of chess_dbs can be opened at the same time.

Databases are created and managed with packs library(db_facts) and library(prosqlite).


The pack also implements boards as dictionaries along with predicates that effect transitions to the board due to moves.

Positions on the board get keys 1-64, and there are keys for: whether various castlings and any en passant are still valid, whose move it is, ply move and half moves since last take.



Integer representation of positions. These hold less information than a board dictionary as we want to make positions that look the same identical, irrespective of when was the last take or at which stage (ply counter) of the game the position arose.

To convert from a dictionary use: chess_dict_inpo/2.

Inpos are used as the first field of game_posi/2 database tables (see Databases section above).

Pack predicates

parsing of and saving to pgn files, and storing/retriving on/from chess_dbs

manage database connections

access db games and info


info interactions


Pack info

- nicos angelopoulos
- 0.1 2018/3/18
- 0.2 2018/3/20
- 0.3 2018/9/14
- 1.0 2021/6/18
See also
- http://stoics.org.uk/~nicos/sware/chess_db
- https://github.com/nicos-angelopoulos/chess_db
- [pack('chess_db/examples/short.pl')]
- pack(prosqlite), pack(db_facts), pack(stoics_lib), pack(options)
To be done
- discard illegal moves when considering possible ones
 chess_db_version(-Version, -Date)
The current version. Version is a Mj:Mn:Fx term, and date is a date(Y,M,D) term.
?- chess_db_version( 1:0:0, date(2021,6,18) ).

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

 pgn(Arg1, Arg2)
 chess_db(Arg1, Arg2)
 chess_db(Arg1, Arg2, Arg3)
 chess_db_ids_pgn(Arg1, Arg2)
 chess_db_connect(Arg1, Arg2)
 chess_db_current(Arg1, Arg2)
 chess_db_game_info(Arg1, Arg2, Arg3)
 chess_db_match(Arg1, Arg2)
 chess_db_opening(Arg1, Arg2)
 chess_db_opening_pgn(Arg1, Arg2)
 chess_db_position(Arg1, Arg2, Arg3)
 chess_db_max_id(Arg1, Arg2)
 chess_dict_inpo(Arg1, Arg2)
 chess_pgn_limos(Arg1, Arg2)
 chess_dict_move(Arg1, Arg2, Arg3)
 chess_dict_move(Arg1, Arg2, Arg3, Arg4)
 chess_dict_piece(Arg1, Arg2, Arg3)
 chess_annotate_freq(Arg1, Arg2, Arg3)
 chess_fen_square(Arg1, Arg2)
 chess_dict_pos_algebraic(Arg1, Arg2)