Exhibit 99.1

                             JOINT FILING AGREEMENT

     The  undersigned  hereby  agree that the  statement  on  Schedule  13G with
respect to the ordinary shares of SAP Aktiengesellschaft  Systeme,  Anwendungen,
Produkte in der  Datenverarbeitung  is, and any amendment thereto signed by each
of the undersigned shall be, filed on behalf of each of the undersigned pursuant
to and in accordance with the provisions of Rule 13d-1(k)  promulgated under the
Securities  Exchange Act of 1934, as amended.  The  undersigned  hereby  further
agree  that this  Joint  Filing  Agreement  be  included  as an  exhibit to such
statement and any such amendment. This Joint Filing Agreement may be executed in
any number of counterparts, all of which taken together shall constitute one and
the same instrument.


Dated: January 28, 2005


                                        /s/ Hasso Plattner
                                       -------------------------------
                                       Dr. Hasso Plattner



                                        Hasso Plattner GmbH & Co.
                                         Beteiligungs-KG
                                        By: Hasso Plattner Verwaltungs-GmbH,
                                            as sole general partner


                                        By: /s/ Hasso Plattner
                                            --------------------------
                                            Name:  Dr. Hasso Plattner
                                            Title:  Managing Director



                                        Hasso Plattner Verwaltungs-GmbH


                                         By: /s/ Hasso Plattner
                                            --------------------------
                                            Name:  Dr. Hasso Plattner
                                            Title:  Managing Director