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=Purposes=
* Save time: Chess programs could use [[Search|search]] from the beginning and look through all possible continuations in detail to find the best next move, but as this is quite time-consuming and there already exists a lot of [https://en.wikipedia.org/wiki/Chess_opening_book_%28literature%29 literature] about different opening lines, opening books save time.
* Provide a higher quality of play. : Searching only even with large depths can't see deep tactics and , strategy, compensation, lose temporarily material for long term advantage.* Provide variety, : as book moves are usually chosen [[Pseudorandom Number Generator|randomly]], whereas searches are more or less deterministic.
=Types=
* [[EPD]]: They are the last positions of opening lines
* [[PGN]]: Opening lines are stored as individual games
<span id="BookBuilder"></span>
* Special formats: In 1999, [[Marc-Philippe Huget]] published a '''Book Builder''' <ref>[https://www.stmintz.com/ccc/index.php?id=44407 Web site updated and new program Book Builder] by [[Marc-Philippe Huget]], [[CCC]], February 24, 1999</ref> in conjunction with his engine [[La Dame Blanche]], a standalone open source program <ref>[http://www.quarkchess.de/ladameblanche/ Book Bilder of La Dame Blanche] by [[Marc-Philippe Huget]], hosted by [[Thomas Mayer]]</ref> to convert a [[Portable Game Notation|PGN file]] into an opening book of the format proposed by [[Kathe Spracklen]] <ref>[[Kathe Spracklen]] ('''1983'''). ''Tutorial: Representation of an Opening Tree''. [[ICGA Journal#6_1|ICCA Newsletter, Vol. 6, No. 1]]</ref>:
<pre>
(e4(e5)(c5))(d4d5)) etc.
</pre>
==Binary==
==Handcrafted==
If the opening database designer has some special preference of a certain opening line, he might create it fully manually. This is often the case if a chess program is about to play an important game against a grandmaster. Then the opening style will probably be chosen to be difficult and dangerous for the opponent. Another option is to first automatically generate a database and then fine -tune it manually.
==AutomatedFrom game collection== Another option is to select a number of games (the type of which will effect affect the openings played: e.g. drawn games only, GM games only, etc) and then up to a certain depth store all positions in the opening database. It is true that by using this way of database generation some severe errors might by copied as well, but usually the chess programs are set to stop playing according from to the book if a position occurred less than a certain number times before.
==By computing==Chess [[engines]] can be used to evaluate positions in a book opening tree to rank them, and/or decide to stop or expand. =Book Building Tools==
* [[Bookbuilder]]
* [[Bookup]]
* [[Chess Opening Wizard]] (COW)
=Quotes=
To solve the opening problems of his chess machine, [[Belle]], [[Ken Thompson]] typed in opening lines from the ''[https://en.wikipedia.org/wiki/Encyclopaedia_of_Chess_Openings Encyclopedia of Chess Openings]'' (in five thick volumes). Religiously, he dedicated one hour a day for almost three years (!) to the tedious pursuit of entering lines of play from the books and having his Belle computer verify them. The result was an opening library of roughly three-hundred thousand moves. The results were immediate and obvious: Belle became a much stronger chess program, and Ken probably aged prematurely. Later Ken developed a program to automatically read the ''Encyclopedia'', allowing him to do in a few days what had taken him three years to do manually. <ref>[[Mathematician#HSBaird|Henry S. Baird]], [[Ken Thompson]] ('''1990'''). ''[http://doc.cat-v.org/bell_labs/reading_chess/ Reading Chess]''. [[IEEE#TPAMI|IEEE Transactions on Pattern Analysis and Machine Intelligence]], Vol. 12, No. 6, [http://doc.cat-v.org/bell_labs/reading_chess/reading_chess.pdf pdf]</ref>
<span id="Formats"></span>
=Formats=
* [[ABK]] - [[Arena|Arena's]] book format
* [http://www.talkchess.com/forum3/viewtopic.php?f=2&t=71764 ChessDBCN] by [[noobpwnftw]], [[CCC]], September 09, 2019
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=72432 Polyglot FRC/960 Opening Book] by [[Dennis Sceviour]], [[CCC]], November 27, 2019 » [[PolyGlot]], [[Chess960]]
==2020 ...==
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=75205 How many Elo points is a book?] by [[Chris Whittington]], [[CCC]], September 25, 2020 » [[Playing Strength]]
=External Links=
