<PAGE>


                                                                 Exhibit 10.63

                            INFORMIX CORPORATION

                   CHANGE OF CONTROL AND SEVERANCE AGREEMENT

    This Change of Control and Severance Agreement (the "Agreement") is made
and entered into by and between Charles W. Chang (the "Executive") and
Informix Corporation (the "Company"), effective as of the last date set forth
by the signatures of the parties below (the "Effective Date").

                                  RECITALS

    A.  It is expected that the Company from time to time will consider the
possibility of an acquisition by another company or other Change of Control
(as defined below). The Board of Directors of the Company (the "Board")
recognizes that such consideration, and the possibility that the Executive's
employment could be terminated by the Company for a reason other than for
cause, can be distractions to the Executive and can cause the Executive to
consider alternative employment opportunities. The Board has determined that
it is in the best interests of the Company and its stockholders to assure
that the Company will have the continued dedication and objectivity of the
Executive, notwithstanding the possibility, threat or occurrence of a Change
of Control of the Company or the termination by the Company of the
Executive's employment for a reason other than for cause.

    B.  The Board believes that it is in the best interests of the Company
and its stockholders to provide the Executive with an incentive to continue
his or her employment with the Company, or a wholly-owned subsidiary of the
Company, as the case may be, and to motivate the Executive to maximize the
value of the Company upon a Change of Control for the benefit of its
stockholders.

    C.  The Board believes that it is imperative to provide the Executive
with certain benefits upon a Change of Control or upon the termination by the
Company of the Executive's employment for a reason other than cause, thereby
encouraging the Executive to remain with the Company notwithstanding the
possibility of a Change of Control or termination of employment for a reason
other than for cause.

    The Company and the Executive hereby agree as follows:

    1.  TERM OF AGREEMENT.  This Agreement shall terminate upon the date that
all obligations of the Company and the Executive with respect to this
Agreement have been satisfied.

<PAGE>

    2.  AT-WILL EMPLOYMENT.  The Company and the Executive acknowledge that
the Executive's employment is and shall continue to be at-will, as defined
under applicable law, and may be terminated at any time by either party, with
or without cause.

    3.  CHANGE OF CONTROL.  In the event a Change of Control occurs within
six months following the effective date of options granted to the Executive
to purchase the Company's common stock, and if the Executive is employed by
the Company as of the date of the Change of Control, the Executive's stock
options shall have their vesting accelerated as to two years' additional
vesting. In the event that stock option vesting is accelerated pursuant to
the preceding sentence, the remaining stock options, if any, shall continue
to vest at a monthly rate equal to the total number of shares originally
subject to the option divided by the number of months in the original vesting
schedule. In the event a Change of Control occurs on or after six months
following the effective date of options granted to the Executive to purchase
the Company's common stock, and if the Executive is employed by the Company
as of the date of the Change of Control, the Executive's Stock Options shall
have their vesting accelerated in full so as to become 100% vested.

    For the purposes of this Agreement, "Change of Control" shall mean:

        (a)  the approval by the stockholders of the Company of a merger or
consolidation of the Company with any other corporation, other than a merger
or consolidation which would result in the voting securities of the Company
outstanding immediately prior thereto continuing to represent (either by
remaining outstanding or by being converted into voting securities of the
surviving entity) fifty percent (50%) or more of the total voting power
represented by the voting securities of the Company or such surviving entity
outstanding immediately after such merger or consolidation; or

         (b)  any approval by the stockholders of the Company of a plan of
complete liquidation of the Company or an agreement for the sale or
disposition by the Company of all or substantially all of the Company's
assets; or

         (c)  any "person" (as that term is used in Sections 13(d) and 14(d)
of the Securities Exchange Act of 1934, as amended) becoming the "beneficial
owner" (as defined in Rule 13d-3 under the Securities Exchange Act of 1934,
as amended), directly or indirectly, of securities of the Company
representing 50% or more of the total voting power represented by the
Company's then outstanding voting securities; or

         (d) a change in the composition of the Board, as a result of which
fewer than a majority of the directors are Incumbent Directors. "Incumbent
Directors" shall mean directors who either: (a) are directors of the Company
as of the Effective Date; or (b) are elected, or nominated for election, to
the Board with the affirmative votes of at least a majority of those
directors whose election or nomination was not in connection with any
transaction described in subsections (a), (b), or (c) above, or in connection
with an actual or threatened proxy contest relating to the election of
directors of the Company.

                                      -2-

<PAGE>

     4.        SEVERANCE.

         (a)   If, within one year of a Change of Control, the Executive's
employment is terminated by the surviving entity for any reason other than
for Cause (as defined below), the Executive shall receive severance in the
amount of one year's base salary plus one year's on target earnings.

         (b)   If, following the one year anniversary of the Executive's
employment by the Company, the Executive's employment is terminated by the
Company for any reason other than for Cause, the Executive shall receive
severance in the amount of one year's base salary.

         (c)   If, following the one year anniversary of the Executive's
employment by the Company, the Executive's employment is terminated by the
Company for Cause, or the Executive voluntarily resigns, the Executive shall
not receive severance.

         (d)   For purposes of this Agreement,"Cause" shall mean the
occurrence of one or more of the following: (i) Executive's conviction by, or
entry of a plea of guilty or NOLO CONTENDRE in, a court of competent
jurisdiction for any crime which constitutes a felony in the jurisdiction in
which the conduct alleged to constitute the felony occurred; (ii)
Executive's misappropriation of funds or property or commission of an act of
fraud, whether prior or subsequent to the Effective Date; (iii) gross
negligence or recklessness by the Executive in the scope of the Executive's
services to the Company; (iv) a breach by the Executive of a material
provision of this Agreement which is not cured within 30 days of notice;(v) a
willful failure by the Executive substantially to perform his or her duties
and responsibilities as an employee after notice of such failure; or (vi) a
material breach by the Executive of the Company's policies or procedures.

     5.  ATTORNEY FEES, COSTS AND EXPENSES. The Company promptly shall
reimburse the Executive, on a monthly basis, for the reasonable attorney
fees, costs and expenses incurred by the Executive in connection with any
action brought by Executive to enforce his or her rights under this Agreement,
regardless of the outcome of the action.

     6.  SUCCESSORS.

         (a)   COMPANY'S SUCCESSORS. Any successor to the Company(whether
direct or indirect and whether by purchase, merger, consolidation,
liquidation or otherwise) to all or substantially all of the Company's
business and/or assets shall assume the obligations under this Agreement and
agree expressly to perform the obligations under this Agreement in the same
manner and to the same extent as the Company would be required to perform
such obligations in the absence of a succession. For all purposes under this
Agreement, the term "Company" shall include any successor to the Company's
business and/or assets which executes and delivers the assumption agreement
described.

                                      -3-

<PAGE>

in this Section 5(a), or which becomes bound by the terms of this Agreement
by operation of law.

          (b)  EXECUTIVE'S SUCCESSORS.  The terms of this Agreement and all
rights of the Executive hereunder shall inure to the benefit of, and be
enforceable by, the Executive's personal or legal representatives, executors,
administrators, heirs, distributees, devisees and legatees.

      7.  MISCELLANEOUS PROVISIONS.

          (a)  WAIVER.  No provision of this Agreement shall be modified,
waived or discharged unless the modification, waiver or discharge is agreed
to in writing and signed by the Executive and by an authorized officer of the
Company (other than the Executive). No waiver by either party of any breach
of, or of compliance with, any condition or provision of this Agreement by
the other party shall be considered a waiver of any other condition or
provision or of the same condition or provision at another time.

          (b)  WHOLE AGREEMENT.  No agreements, representations or
understandings (whether oral or written and whether expressed or implied)
which are not expressly set forth in this Agreement have been made or entered
into by either party with respect to the subject matter hereof. This
Agreement represents the entire understanding of the Company and the
Executive with respect to the subject matter of this Agreement and this
Agreement supersedes all prior agreements, arrangements and understandings
regarding the subject matter of this Agreement. If stock option vesting
acceleration is triggered pursuant to this Agreement, the Executive agrees
that he or she shall not be entitled to any additional stock option vesting
pursuant to a prior agreement, arrangement or understanding.

          (c)  CHOICE OF LAW.  The validity, interpretation, construction and
performance of this Agreement shall be governed by the laws of the State of
California.

          (d)  SEVERABILITY.  The invalidity or unenforceability of any
provision or provisions of this Agreement shall not affect the validity or
enforceability of any other provision hereof, which shall remain in full
force and effect.

          (e)  COUNTERPARTS.  This Agreement may be executed in counterparts,
each of which shall be deemed an original, but all of which together will
constitute one and the same instrument.

                                       -4-

<PAGE>

    IN WITNESS WHEREOF, each of the parties has executed this
Agreement, in the case of the Company by its duly authorized officer, as of
the day and year set forth below.


COMPANY                                INFORMIX CORPORATION



                                       /s/ [ILLEGIBLE]

                                       ---------------------------------------

                                       Dated:  Effective December 15, 1999


EXECUTIVE                             /s/ [ILLEGIBLE]
                                      ----------------------------------------

                                       Dated:  Effective December 15, 1999



                                      -5-