Changes

There are two three ways to store an opening database:

* PositionsLast positions* All positions

Some [[Databases|databases]] use a list of common opening lines(usually stored in PGN files), while others hold a list of last positions (usually stored in EDP files) that arise in common openings. The first option is two options are probably easier to implementand understand by human, while the second third has some important advantages, especially for computer chess engines.

Opening databases built on all positions are usually more space efficient and overcome the problem of [[Transposition|transpositions]]. Often these positions are stored as hash value to allow fast access. Some opening database formats store with each positions position as well some information about it. (e.g. number of times occurred, number of games won by white/black / drawn with this position, average/maximum Elo of players playing to this opening position, chess program's success with the position) . So when a chess program has to decide on a move, it will look up all positions that could arise after moving in the database and then make a decision upon the information given with each position.