Changes

Each database node has a persistent ''id'' value, which remains valid after update operations, and which is referenced by the [[Indexes#Value Indexes|value indexes]]. As long as no updates are performed on a database, the ''pre'' and ''id'' values are identical. The values will remain to be identical if new nodes are exclusively added to the end of the database. If nodes are deleted or inserted somewhere else, the values will diverge, as shown in the next example:

$ basex -c"create db db <xml>HiThere</xml>" -q"insert node <b/> before /xml" -c"info storage"

2 2 2 1 1 0 ELEM xml

3 1 1 1 2 0 TEXT HiThere

The [[Database Module#db:node-pre|db:node-pre]] and [[Database Module#db:node-id|db:node-id]] functions can be called to retrieve the ''pre'' and ''id'' values of a node, and [[Database Module#db:open-pre|db:open-pre]] and [[Database Module#db:open-id|db:open-id]] can be used to go back and retrieve the original node. By default, ''id'' lookups are expensive. If {{Option|UPDINDEX}} is turned on, an additional index will be maintained to speed up the process.