 255 different segment types, on up to 15 levels, are allowed in any database.A database "record" consists of a specific root segment and all its dependent child segments there is no limit to the number of segments in a record, or to the number of records in a database (apart from physical limitations of storage space).The structure of any database is presented to the application program as a "PCB" (Program Communication Block), and this is used as one of the parameters passed to the stub.