1. A method, in a computer system, for mapping an X500 data model comprising at least one entry ( 7 ), at least one object class, and a directory information tree, DIT ( 6 ), an entry ( 7 ) comprising at least one attribute ( 8 ), an attribute ( 8 ) comprising a type ( 9 ) and a value ( 10 ), said entry ( 7 ) gathering information about one object, an object class being a model defining the types of said attributes ( 8 ) present in the entry ( 7 ) that describes said object, the vertices in said DIT ( 6 ), being entries ( 7 ), each entry ( 7 ) comprising a distinguished name, DN, comprising the DN of said parent's entry in said DIT ( 6 ) together with a relative distinguished name, RDN, comprising one specially nominated attribute ( 8 ) proper to said entry ( 7 ), onto a relational database, RDB, comprising relational tables ( 11 ), each table ( 11 ) comprising several named columns ( 14 ), some of these columns being primary key, that is containing value that uniquely identify object data, where object data is stored in row ( 15 ), characterized in that it comprises the steps of: building object classes, each comprising a list of its attributes ( 8 ), building attributes ( 8 ), each comprising its type ( 9 ), building a static directory information tree, SDIT, comprising only static DN, SDN, that is DN comprising only static RDN, that is RDN with any variable value removed, mapping X500 data to RDB by associating an X500 object class to a RDB table ( 11 ) an X500 attribute ( 8 ) to a RDB table column ( 14 ) and storing the name ( 13 ) of said table column ( 14 ) with said X500 attribute ( 8 ), as an address pointing to said attribute ( 8 ).