A method and arrangement(700) for a hierarchical database (702) comprising a root table and sub-tables in hierarchical levels, each table comprising one or more attributes under which object data can be stored.A configuring function (708) assigns to each sub-table a table identifier TID generated by multiplying a series of prime numbers associated with parent tables of that sub-table. A storing function (704) assigns an object identifier OID to each object in the database such that the table identifiers TID:s of a path of hierarchically connected sub-tables indifferent consecutive levels are encoded into the object identifier OID, and stores data on that object in the connected sub-tables in the table path.