An index is a list of index values and row IDs (ROWIDs). ROWIDs are physical pointers to the database tables that give you the fastest access to rows. ROWIDs do not change during the life of a row—they only change when you dump and reload a database. If you delete a row and create a new identical row, it might have a different ROWID. The database blocks of an index are organized into a tree structure for fast access. OpenEdge locates rows within an index by traversing the index tree. Once a row is located, the ROWID accesses the data. OpenEdge does not lock the whole index tree while it looks for the row, it only locks the block that contains the row. Therefore, other users can simultaneously access rows in the same database.