The present invention provides a database system having a database in which data to be processed by an application program are stored (hierarchical node database). A table (hierarchical link table) in which mainly relationship data (e.g., a pointer) for the database are entered is prepared for a corresponding application program. The individual application programs can refer to the corresponding hierarchical link tables and can access desired hierarchical node databases. When the hierarchical data structure is to be changed, such as by the addition of an application due to a new request, a corresponding alteration need only be reflected in the hierarchical link table.