MIDS(mutitmedia intelligent database system) is an object database management system．Its database programming language is P++，which is based on C++．In the implementation of P++ the authors encountered the following problems：First，C++ pointer is ambiguous，not only can member pointer and reference pointer not be distinguished in semantics，but also volatile pointer and persistent pointer．This pointer ambiguity results in object locking problem in transaction management and others．Second, C++ objects that have virtual functions or virtual base classes contain memory pointers, which were not specified by the programmer．If such C++ objects are made persistent，then these pointers may be invalid across program invocations．Last，If the authors store object using file system call services，they should design complicated cache subsystem and a large amount of object format transformation，which demand a lot of memory and time．So they must find another solution storage scheme based on virtual memory mapping．