EXHIBIT 3.1


                                 DDI MERGER CO.

                          CERTIFICATE OF INCORPORATION


                                   ARTICLE I
                                   ---------

     The name of this corporation is "DDi Merger Co." (hereinafter referred to
as the "Corporation").

                                   ARTICLE II
                                   ----------

     The registered office of this corporation in the State of Delaware is
located at 1013 Centre Road, in the City of Wilmington, County of New Castle.
The name of its registered agent at such address is Corporation Service Company.

                                  ARTICLE III
                                  -----------

     The purpose of this Corporation is to engage in any lawful act or activity
for which corporations may be organized under the General Corporation Law of
Delaware.

                                   ARTICLE IV
                                   ----------

     The name and mailing address of the incorporator is as follows:

                               Sarah H. McCready
                                   Paralegal
                                  Ropes & Gray
                            One International Place
                             Boston, MA  02110-2624

                                   ARTICLE V
                                   ---------

     The total number of shares of all classes of stock which the Corporation
shall have authority to issue is 80,000,000 shares, consisting of (i) 75,000,000
shares of Common Stock, $.01 par value per share ("Common Stock"), and (ii)
5,000,000 shares of Preferred Stock, $.001 par value per share ("Preferred
Stock").

                                      -1-


     The following is a statement of the designations and the powers, privileges
and rights, and the qualifications, limitations or restrictions thereof in
respect of each class of capital stock of the Corporation.

     1.   Common Stock.

     A.   General.  Subject to the powers, preferences and rights of any
          -------
          Preferred Stock, including any series thereof, having any preference
          or priority over, or rights superior to, the Common Stock and except
          as otherwise provided by law and this Article, the holders of the
          Common Stock shall have and possess all powers and voting and other
          rights pertaining to the stock of the corporation and each share of
          Common Stock shall be entitled to one vote. Except as otherwise
          provided by the Delaware General Corporation Law or this Certificate
          of Incorporation, the holders of record of Common Stock shall share
          ratably in all dividends payable in cash, stock or otherwise and other
          distributions, whether in respect of liquidation or dissolution
          (voluntary or involuntary) or otherwise. The holders of the Common
          Stock shall have no preemptive rights to subscribe for any shares of
          any class of stock of this Corporation whether now or hereafter
          authorized.

     B.   Voting.  The holders of the Common Stock are entitled to one vote for
          ------
          each share of Common Stock held at all meetings of stockholders.
          There shall be no cumulative voting.

     C.   Number.  The number of authorized shares of Common Stock may be
          ------
          increased or decreased (but not below the number of shares thereof
          then outstanding) by the affirmative vote of the holders of a majority
          of the stock of the Corporation entitled to vote, irrespective of the
          provisions of Section 242(b)(2) of the General Corporation Law of the
          State of Delaware.

     D.   Dividends.  Dividends may be declared and paid on the Common Stock
          ---------
          from funds lawfully available therefor as and when determined by
          the Board of Directors and subject to any preferential dividend rights
          of any then outstanding Preferred Stock.

     E.   Liquidation.  Upon the dissolution or liquidation of the Corporation,
          -----------
          whether voluntary or involuntary, holders of Common Stock will be
          entitled to receive all assets of the Corporation available for
          distribution to its stockholders, subject to any preferential rights
          of any then outstanding Preferred Stock.

                                      -2-


     2.   Preferred Stock.
          ---------------

     Preferred Stock may be issued from time to time in one or more series, each
of such series to have such terms as stated or expressed herein and in the
resolution or resolutions providing for the issue of such series adopted by the
Board of Directors of the Corporation as hereinafter provided.  Any shares of
Preferred Stock which may be redeemed, purchased or acquired by the Corporation
may be reissued except as otherwise provided by law or this Certificate of
Incorporation.  Different series of Preferred Stock shall not be construed to
constitute different classes of shares for the purposes of voting by classes
unless expressly provided in the resolution or resolutions providing for the
issue of such series adopted by the Board of Directors as hereinafter provided.

     Authority is hereby expressly granted to the Board of Directors from time
to time to issue the Preferred Stock in one or more series, and in connection
with the creation of any such series, by resolution or resolutions providing for
the issue of the shares thereof, to determine and fix such voting powers, full
or limited, or no voting powers, and such designations, preferences and relative
participating, optional or other special rights, and qualifications, limitations
or restrictions thereof, including without limitation thereof, dividend rights,
conversion rights, redemption privileges and liquidation preferences, as shall
be stated and expressed in such resolutions, all to the full extent now or
hereafter permitted by the General Corporation Law of the State of Delaware.
Without limiting the generality of the foregoing, the resolutions providing for
issuance of any series of Preferred Stock may provide that such series shall be
superior or rank equally or be junior to the Preferred Stock of any other series
to the extent permitted by law and this Certificate of Incorporation.  Except as
otherwise provided in this Certificate of Incorporation, no vote of the holders
of the Preferred Stock or Common Stock shall be a prerequisite to the
designation or issuance of any shares of any series of the Preferred Stock
authorized by and complying with the conditions of this Certificate of
Incorporation, the right to have such vote being expressly waived by all present
and future holders of the capital stock of the Corporation.

                                   ARTICLE VI
                                   ----------

     The Corporation shall have a perpetual existence.

                                  ARTICLE VII
                                  ------------

     Unless and except to the extent that the By-Laws of this Corporation shall
so require, the election of directors need not be by written ballot.

                                      -3-


                                  ARTICLE VII
                                  -----------

     In furtherance of and not in limitation of the powers conferred by statute,
the Board of Directors is expressly authorized to adopt, amend or repeal the By-
Laws of this Corporation, subject to the right of the stockholders entitled to
vote with respect thereto to alter and repeal the By-Laws adopted or amended by
the Board of Directors; provided, however, that, notwithstanding the fact that a
                        --------  -------
lesser percentage may be specified by law, the By-Laws shall not be altered,
amended or repealed by the stockholders of the Corporation except by the
affirmative vote of holders of not less than seventy-five percent (75%) of the
then outstanding shares of capital stock of the Corporation entitled to vote
generally in the election of directors, unless such alteration, amendment or
repeal has been approved by a majority of those directors who are (i) not
affiliated or associated with any person or entity holding 10% or more of the
voting power of our outstanding capital stock, or (ii) affiliated or associated
with the Bain Capital Funds. The Bain Capital Funds shall mean Bain Capital Fund
V, L.P., Bain Capital Fund V-B, L.P., BCIP Associates, BCIP Trust Associates,
and any other entity which receives investment advice from an advisor or
subadvisor to any of those entities or from an affiliate of such advisor or
subadvisor.

                                  ARTICLE IX
                                  ----------

     Except to the extent that the General Corporation Law of the State of
Delaware prohibits the elimination or limitation of liability of directors for
breaches of fiduciary duty, no director of the Corporation shall be personally
liable to the Corporation or its stockholders for monetary damages for any
breach of fiduciary duty as a director, notwithstanding any provision of law
imposing such liability.  No amendment to or repeal of this provision shall
apply to or have any effect on the liability or alleged liability of any
director of the Corporation for or with respect to any acts or omissions of such
director occurring prior to such amendment.

                                   ARTICLE X
                                   ---------

1.   Indemnification.  The Corporation shall, to the maximum extent permitted
     ---------------
under the General Corporation Law of the State of Delaware and except as set
forth below, indemnify, hold harmless and, upon request, advance expenses to
each person (and the heirs, executors or administrators of such person) who was
or is a party or is threatened to be made a party to any threatened, pending or
completed action, suit or proceeding, whether civil, criminal, administrative or
investigative, by reason of the fact that he or she is or was, or has agreed to
become, a director or officer of the Corporation, or is or was serving, or has
agreed to serve, at the request of the Corporation, as a director, officer or
trustee of, or in a similar capacity with, another corporation, partnership,
joint venture, trust or other enterprise, including any employee benefit plan
(any such person being referred to hereafter as an "Indemnitee"), or by reason
of any action alleged to have been taken or omitted in such capacity, against
all expenses (including attorneys' fees), judgments, fines and amounts paid in
settlement actually and reasonably incurred by him or her or on his or her
behalf in connection with such action, suit or proceeding and any

                                      -4-


appeal therefrom, if he or she acted in good faith and in a manner he or she
reasonably believed to be in, or not opposed to, the best interests of the
Corporation, and, with respect to any criminal action or proceeding, had no
reasonable cause to believe his or her conduct was unlawful. Notwithstanding
anything to the contrary in this Article, the Corporation shall not indemnify an
Indemnitee seeking indemnification in connection with any action, suit,
proceeding, claim or counterclaim, or part thereof, initiated by the Indemnitee
unless the initiation thereof was approved by the Board of Directors of the
Corporation.

2.   Advance of Expenses. Notwithstanding any other provisions, this Certificate
     -------------------
of Incorporation, the By-Laws of the Corporation, or any agreement, vote of
stockholder or disinterested directors, or arrangement to the contrary, the
Corporation shall advance payment of expenses incurred by an Indemnitee in
advance of the final disposition of any matter only upon receipt of an
undertaking by or on behalf of the Indemnitee to repay all amounts so advanced
in the event that it shall ultimately be determined that the Indemnitee is not
entitled to be indemnified by the Corporation as authorized in this Article.
Such undertaking may be accepted without reference to the financial ability of
the Indemnitee to make such repayment.

3.   Subsequent Amendment.  No amendment, termination or repeal of this Article
     --------------------
or of the relevant provisions of the General Corporation Law of the State of
Delaware or any other applicable laws shall affect or diminish in any way the
rights of any Indemnitee to indemnification under the provisions hereof with
respect to any action, suit, proceeding or investigation arising out of or
relating to any actions, transactions or facts occurring prior to the final
adoption of such amendment, termination or repeal.

4.   Other Rights.  The Corporation may, to the extent authorized from time to
     ------------
time by its Board of Directors, grant indemnification rights to other employees
or agents of the Corporation or other persons serving the Corporation and such
rights may be equivalent to, or greater or less than, those set forth in this
Article.

5.   Reliance.   Persons who after the date of the adoption of this provision
     --------
become or remain directors or officers of the Corporation or who, while a
director or officer of the Corporation, become or remain a director, officer,
employee or agent of a subsidiary, shall be conclusively presumed to have relied
on the rights to indemnity, advance of expenses and other rights contained in
this Article in entering into or continuing such service.  The rights to
indemnification and to the advance of expenses conferred in this Article shall
apply to claims made against an indemnitee arising out of acts or omissions
which occurred or occur both prior and subsequent to the adoption hereof.

6.   Merger or Consolidation.  If the Corporation is merged into or consolidated
     -----------------------
with another corporation and the Corporation is not the surviving corporation,
the surviving corporation shall assume the obligations of the Corporation under
this Article with respect to any action, suit, proceeding or investigation
arising out of or relating to any actions, transactions or facts occurring prior
to the date of such merger or consolidation.

                                      -5-


7.   Insurance.  The Corporation shall have power to purchase and maintain
     ---------
insurance on behalf of any person who is or was, or has agreed to become, a
director, officer, employee or agent of the Corporation, or is or was serving,
or has agreed to serve, at the request of the Corporation as a director,
officer, employee, agent or trustee of another corporation, partnership, joint
venture, trust or other enterprise, including any employee benefit plan, against
all expenses (including attorney's fees) judgments, fines or amounts paid in
settlement incurred by such person in any such capacity or arising out of his or
her status as such, whether or not the Corporation would have the power to
indemnify him or her against such expenses under the General Corporation Law of
the State of Delaware.

8.   Savings Clause.  If this Article or any portion hereof shall be invalidated
     --------------
on any ground by any court of competent jurisdiction, then the Corporation shall
nevertheless indemnify each Indemnitee as to any expenses, including attorneys'
fees, judgments, fines and amounts paid in settlement in connection with any
action, suit, proceeding or investigation, whether civil, criminal or
administrative, including an action by or in the right of the Corporation, to
the fullest extent permitted by any applicable portion of this Article that
shall not have been invalidated and to the fullest extent permitted by
applicable law.

                                   ARTICLE XI
                                   ----------

     The Corporation reserves the right to amend, alter, change or repeal any
provision contained in this Certificate of Incorporation, in the manner now or
hereafter prescribed by statute and this Certificate of Incorporation, and all
rights conferred upon stockholders herein are granted subject to this
reservation.

                                  ARTICLE XII
                                  -----------

     This Article is inserted for the management of the business and for the
conduct of the affairs of the Corporation.

     1.   Number of Directors.  The number of directors of the Corporation shall
          -------------------
          not be less than three.  The exact number of directors within the
          limitations specified in the preceding sentence shall be fixed from
          time to time by, or in the manner provided in, the By-Laws of the
          Corporation.

     2.   Classes of Directors.  The Board of Directors shall be and is divided
          --------------------
          into three classes:  Class I, Class II and Class III.  No one class
          shall have more than one director more than any other class.  If a
          fraction is contained in the quotient arrived at by dividing the
          designated number of directors by three, then, if such fraction is
          one-third, the extra director shall be a member of Class III, and if
          such fraction is two-thirds, one of the extra directors shall be a
          member of Class III and one of the extra directors shall be a member
          of Class II, unless otherwise provided from time to time by resolution
          adopted by the Board of Directors.

                                      -6-


     3.   Election of Directors.  Elections of directors need not be by written
          ---------------------
          ballot except as and to the extent provided in the By-Laws of the
          Corporation.

     4.   Terms of Office.  Except as provided in Section 6 of this Article XI,
          ---------------
          each director shall serve for a term ending on the date of the third
          annual meeting following the annual meeting at which such director was
          elected; provided, however, that each initial director in Class I
                   --------  -------
          shall serve for a term ending on the date of the annual meeting in
          2001; each initial director in Class II shall serve for a term ending
          on the date of the annual meeting in 2002; and each initial director
          in Class III shall serve for a term ending on the date of the annual
          meeting in 2003; and provided, further, that the term of each director
                               --------  -------
          shall be subject to the election and qualification of his or her
          successor and to his or her earlier death, resignation or removal.

     5.   Allocation of Directors Among Classes in the Event of Increases or
          ------------------------------------------------------------------
          Decreases in the Number of Directors.  In the event of any increase or
          ------------------------------------
          decrease in the authorized number of directors, (i) each director then
          serving as such shall nevertheless continue as a director of the class
          of which he or she is a member and (ii) the newly created or
          eliminated directorships resulting from such increase or decrease
          shall be apportioned by the Board of Directors among the three classes
          of directors so as to ensure that no one class has more than one
          director more than any other class. To the extent possible, consistent
          with the foregoing rule, any newly created directorships shall be
          added to those classes whose terms of office are to expire at the
          latest dates following such allocation, and any newly eliminated
          directorships shall be subtracted from those classes whose terms of
          offices are to expire at the earliest dates following such allocation,
          unless otherwise provided from time to time by resolution adopted by
          the Board of Directors.

     6.   Removal.  The directors of the Corporation may not be removed without
          -------
          cause and may be removed for cause only by the affirmative vote of the
          holders of at least seventy-five percent (75%) of the shares of the
          capital stock of the Corporation issued and outstanding and entitled
          to vote generally in the election of directors cast at a meeting of
          the stockholders called for that purpose, notwithstanding the fact
          that a lesser percentage may be specified by law.

                                      -7-


     7.   Vacancies.   Any vacancy in the Board of Directors, however occurring,
          ---------
          including a vacancy resulting from an enlargement of the Board, shall
          be filled only by vote of a majority of the directors then in office,
          although less than a quorum, or by a sole remaining director.  A
          director elected to fill a vacancy shall be elected for the unexpired
          term of his or her predecessor in office, and a director chosen to
          fill a position resulting from an increase in the number of directors
          shall hold office until the next election of the class for which such
          director shall have been chosen, subject to the election and
          qualification of his or her successor and to his or her earlier death,
          resignation or removal.

     8.   Stockholder Nominations and Introduction of Business, Etc.  Advance
          ----------------------------------------------------------
          notice of stockholder nominations for election of directors and other
          business to be brought by stockholders before either an annual or
          special meeting of stockholders shall be given in the manner provided
          by the By-Laws of this Corporation.

     9.   Amendment to Article.  Notwithstanding any other provisions of law,
          --------------------
          this Certificate of Incorporation or the By-Laws, each as amended, and
          notwithstanding the fact that a lesser percentage may be specified by
          law, this Certificate of Incorporation or the By-Laws of the
          Corporation, the affirmative vote of least seventy-five percent (75%)
          of the then outstanding shares of capital stock of the Corporation
          entitled to vote generally in the election of directors shall be
          required to amend or repeal, or to adopt any provisions inconsistent
          with the purpose or intent of, this Article XII, unless such
          amendment, repeal or adoption has been approved by a majority of those
          directors who are (i) not affiliated or associated with any person or
          entity holding 10% or more of the voting power of our outstanding
          capital stock or (ii) affiliated or associated with the Bain Capital
          Funds.

                                  ARTICLE XII
                                  -----------

1.   Dividends.  The Board of Directors shall have authority from time to time
     ---------
to set apart out of any assets of the Corporation otherwise available for
dividends a reserve or reserves as working capital or for any other purpose or
purposes, and to abolish or add to any such reserve or reserves from time to
time as said board may deem to be in the interest of the Corporation; and said
Board shall likewise have power to determine in its discretion, except as herein
otherwise provided, what part of the assets of the Corporation available for
dividends in excess of such reserve or reserves shall be declared in dividends
and paid to the stockholders of the Corporation.

2.   Issuance of Stock.  The shares of all classes of stock of the Corporation
     -----------------
may be issued by the Corporation from time to time for such consideration as
from time to time may be fixed by the Board of Directors of the Corporation,
provided that shares of stock having a par value shall not be issued for a
consideration less than such par value, as determined by the Board. At any time,
or from time to time, the Corporation may grant rights or options to purchase
from the Corporation any shares of its stock of any class or classes to run for
such period of time,

                                      -8-


for such consideration, upon such terms and conditions, and in such form as the
Board of Directors may determine. The Board of Directors shall have authority,
as provided by law, to determine that only a part of the consideration which
shall be received by the Corporation for the shares of its stock which it shall
issue from time to time, shall be capital; provided, however, that, if all the
shares issued shall be shares having a par value, the amount of the part of such
consideration so determined to be capital shall be equal to the aggregate par
value of such shares. The excess, if any, at any time, of the total net assets
of the Corporation over the amount so determined to be capital, as aforesaid,
shall be surplus. All classes of stock of the Corporation shall be and remain at
all times nonassessable.

     The Board of Directors is hereby expressly authorized, in its discretion,
in connection with the issuance of any obligations or stock of the Corporation
(but without intending hereby to limit its general power so to do in other
cases), to grant rights or options to purchase stock of the Corporation of any
class upon such terms and during such period as the Board of Directors shall
determine, and to cause such rights to be evidenced by such warrants or other
instruments as it may deem advisable.

3.   Inspection of Books and Records.  The Board of Directors shall have power
     -------------------------------
from time to time to determine to what extent and at what times and places and
under what conditions and regulations the accounts and books of the Corporation,
or any of them, shall be open to the inspection of the stockholders; and no
stockholder shall have any right to inspect any account or book or document of
the Corporation, except as conferred by the laws of the State of Delaware,
unless and until authorized so to do by resolution of the Board of Directors or
of the stockholders of the Corporation.

4.   Location of Meetings, Books and Records.  Except as otherwise provided in
     ---------------------------------------
the By-laws, the stockholders of the Corporation and the Board of Directors may
hold their meetings and have an office or offices outside of the State of
Delaware and, subject to the provisions of the laws of said State, may keep the
books of the Corporation outside of said State at such places as may, from time
to time, be designated by the Board of Directors or by the By-laws of this
Corporation.

                                  ARTICLE XIV
                                  -----------

     At any time during which a class of capital stock of this Corporation is
registered under Section 12 of the Securities Exchange Act of 1934 or any
similar successor statute, stockholders of the Corporation may not take any
action by written consent in lieu of a meeting. Notwithstanding any other
provisions of law, this Certificate of Incorporation or the By-Laws, each as
amended, and notwithstanding the fact that a lesser percentage may be specified
by law, this Certificate of Incorporation or the By-Laws of the Corporation, the
affirmative vote of seventy-five percent (75%) of the then outstanding shares of
capital stock of the Corporation entitled to vote generally in the election of
directors shall be required to amend or repeal, or to adopt any provisions
inconsistent with the purpose or intent of, this Article XIV, unless such
amendment, repeal or adoption has been approved by a majority of those directors
who are (i) not affiliated or associated with any person or entity holding 10%
or more of the voting power of our outstanding capital stock or (ii) affiliated
or associated with the Bain Capital Funds.

                                      -9-


                                   ARTICLE XV
                                   ----------

     Special meetings of stockholders may be called at any time by only the
Chairman of the Board of Directors, the Chief Executive Officer (or if there is
no Chief Executive Officer, the President), or by the Board of Directors of the
Corporation pursuant to a resolution adopted by the affirmative vote of a
majority of the total number of directors then in office.  Any business
transacted at any special meeting of stockholders shall be limited to matters
relating to the purpose or purposes stated in the notice of meeting.
Notwithstanding any other provisions of law, this Certificate of Incorporation
or the By-Laws, each as amended, and notwithstanding the fact that a lesser
percentage may be specified by law, this Certificate of Incorporation or the By-
Laws of the Corporation, the affirmative vote of seventy-five percent (75%) of
the then outstanding shares of capital stock of the Corporation entitled to vote
generally in the election of directors shall be required to amend or repeal, or
to adopt any provisions inconsistent with the purpose or intent of, this Article
XV, unless such amendment, repeal or adoption has been approved by a majority of
those directors who are (i) not affiliated or associated with any person or
entity holding 10% or more of the voting power of our outstanding capital stock
or (ii) affiliated or associated with the Bain Capital Funds.

                                  ARTICLE XVI
                                  -----------

     The Board of Directors of this Corporation, when evaluating any offer of
another party to make a tender or exchange offer for any equity security of the
Corporation, shall, in connection with the exercise of its judgment in
determining what is in the best interests of the Corporation as a whole, be
authorized to give due consideration to any such factors as the Board of
Directors determines to be relevant, including without limitation: (i) the
interests of the stockholders of the Corporation; (ii) whether the proposed
transaction might violate federal or state laws; (iii) not only the
consideration being offered in the proposed transaction, in relation of the then
current market price for the outstanding capital stock of the Corporation, but
also to the market price for the capital stock of the Corporation over a period
of years, the estimated price that might be achieved in a negotiated sale of the
Corporation as a whole or in part or through orderly liquidation, the premiums
over market price for the securities of other corporations in similar
transactions, current political, economic and other factors bearing on
securities prices and the Corporation's financial condition and future
prospects; and (iv) the social, legal and economic effects upon employees,
suppliers, customers and others having similar relationships with the
Corporation, and the communities in which the Corporation conducts its business.

                                      -10-


     In connection with any such evaluation, the Board of Directors is
authorized to conduct such investigations and to engage in such legal
proceedings as the Board of Directors may determine.

                                  ARTICLE XVI
                                  -----------

     The Corporation expressly elects to be governed by Section 203 of the
Delaware General Corporation Law.  Notwithstanding the terms of Section 203 of
the Delaware General Corporation Law and without regard to the percentage of
voting stock of the Corporation owned at any time by the Bain Capital Funds, the
Bain Capital Funds shall not be deemed at any time to be an "interested
stockholder" as such term is defined in Section 203(c)(5) of the Delaware
General Corporation Law.

                    *    *    *     *    *    *

     THE UNDERSIGNED, the sole incorporator named above, hereby certifies that
the facts stated above are true as of this twentieth day of March, 2000.


                                         /s/ SARAH H. McCREADY
                                         ------------------------------
                                         Sarah H. McCready
                                         Sole Incorporator

                                      -11-