A computer-implemented data management method, encryption system and interactive computer program for managing real estate information in a hierarchical database are disclosed. Also, a method, system and program for cross referencing a hierarchical database with a relational database are disclosed. A computer program accesses an XML definitional document on a handheld computer for inputting data related to real estate listings in a hierarchically controlled format for a database. Real estate agents provide input of data to the database using the handheld, portable computer. A menu or picklist driven display provides logical selection of data input and address fields, and a validation step for checking errors or omissions in the data entry procedure for a given record. A single, central database table is managed for input and distribution of real estate listing information to subscribers to the database management system.