MERCATOR SOFTWARE, INC.

August 7, 2003

Kenneth J. Hall
[address]

Dear Ken:

         This is an agreement ("Agreement") that has been reached with you in
connection with your continued employment with Mercator Software, Inc. (the
"Company"). Capitalized terms not defined herein shall have the meanings given
thereto in that certain Agreement and Plan of Merger (the "Merger Agreement"),
dated as of August 2, 2003, by and among Ascential Software Corporation, a
Delaware corporation ("Ascential"), Greek Acquisition Corporation, a Delaware
corporation and wholly owned subsidiary of Ascential, and the Company.

         1.       You and the Company agree that if: (i) you either (a) continue
                  to remain employed by the Company from the date hereof until
                  the end of the sixty (60) day period following the
                  consummation of the currently contemplated tender offer to be
                  undertaken by Ascential ("Offer") or (b) do not remain
                  employed for such period as a result of your death, disability
                  (which means you become eligible for long-term disability
                  benefits under the Company's long-term disability plan) or the
                  termination of your employment by the Company other than for
                  "cause" (as defined in the June 28, 2001 employment agreement
                  between you and the Company), and (ii) you execute the Form of
                  Release as set forth in Exhibit A, then the cash severance
                  benefits (other than the "pro-rated bonus") set forth in
                  Exhibit B attached hereto (assuming termination on November
                  15, 2003) will be payable to you semi-monthly over twelve (12)
                  months rather than payable semi-monthly over eighteen (18)
                  months. Notwithstanding anything contained in the previous
                  sentence, (i) the "pro-rated bonus" described in Exhibit B
                  will be paid to you within 45 days following any termination
                  of your employment (other than a termination of your
                  employment by the Company for "cause" (as defined in the June
                  28, 2001 employment agreement between you and the Company)),
                  and (ii) the "executive benefits" set forth in Exhibit B will
                  continue to be provided to you for a period of eighteen (18)
                  months following any termination of your employment (other
                  than a termination of your employment by the Company for
                  "cause" (as defined in the June 28, 2001 employment agreement
                  between you and the Company)).

         2.       You and the Company agree that the period within which you are
                  required to give notice to the Company of the occurrence of
                  "good

                  reason," as defined in the June 28, 2001 employment agreement
                  between you and the Company or pursuant to the Company's
                  Change of Control Benefits Plan (the "Plan"), has been
                  extended from thirty (30) days to sixty (60) days following
                  the occurrence of any such "good reason."

         3.       Nothing contained herein shall be construed as a waiver of any
                  rights which you may have under any such employment agreement
                  or the Plan or an amendment of such Plan or agreement,
                  including (without limitation) the treatment of any stock
                  options held by you as described in Exhibit B.

         4.       Exhibit B contains a statement of the amount and payment terms
                  of your benefits assuming you are terminated effective
                  November 15, 2003. The amounts are subject to adjustment
                  depending on the actual date of termination in accordance with
                  the terms and conditions of the applicable employment
                  agreement and/or Plan. The terms and conditions of the
                  payments of such amounts will be governed by this agreement,
                  the Plan and any employment agreement between you and the
                  Company.

         5.       In the event the Offer is not consummated, this Agreement
                  shall be null and void and of no force or effect.


         If the above sets forth our agreement as you understand it and consent
to it, please so signify by executing the enclosed copy of this letter and
return it to me at the address listed above.

         Mercator Software, Inc.

         /s/
         ----------------------
         Name:
         Title:



Agreed to and Accepted:

         /s/ Kenneth J. Hall
         ----------------------
         Name:  Kenneth J. Hall

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