KEY EMPLOYEE AGREEMENT

July 30, 2003

Mark Register

Dear Mark:

We are pleased that you want to join the Ascential team. Subject to and
conditioned upon the completion and closing of the currently contemplated tender
offer transaction involving Mercator Software, Inc. ("Mercator") and Ascential
Software Corporation ("Ascential"), (the "Transaction") the following lists the
terms of your employment by Ascential following the closing. The following is
also conditioned upon your keeping the contents and existence of this letter
completely confidential, other than from your personal legal and financial
advisors.

Effective as of the day after the closing of the Transaction, we propose that
you begin employment in the position of Chief Marketing Officer, in our
Westborough, MA office, reporting to Pete Fiore, President. Your annual base
salary, effective the day after the closing of the Transaction, will be
$250,000.00, paid in equal semi monthly installments, less applicable tax
withholding and other deductions. As a full-time employee, you will also be
eligible to participate in the Ascential Key Employee Incentive Plan ("KEIP"),
with an initial annual target bonus amount of up to 50% of your base salary in
accordance with the terms of the KEIP. For fiscal year 2003, you will be
eligible to participate in the KEIP as if your employment with Ascential started
January 1, 2003. This is also conditional upon your agreement that your current
Mercator Software ex-patriot program (described in a letter dated 1 August 2002)
will end as of the closing of the Transaction.

Your Mercator options will be treated in accordance with the Transaction
documents. In addition, following the closing of the Transaction, you will
receive a grant of a non-qualified option to purchase 50,000 shares of the $.01
par value common stock of Ascential (the "Common Stock") under an Ascential
stock option plan. The option will have a per share exercise price equal to the
closing price of the Common Stock on the date of the option grant. The options
will be governed by the terms of the applicable Ascential option plan and award
agreement and will begin vesting on the day you are first employed by Ascential
and will continue to vest according to Ascential's regular vesting schedule.
Upon the closing of the Transaction you will be eligible for a Change in Control
Agreement in the form attached hereto, to be signed on your first day of
fulltime employment by Ascential.

Although an evaluation process is still ongoing and there may be a transition
period following the Transaction, employees will eventually be transitioned to
Ascential's medical insurance, dental benefit, life and disability insurance
plans following the Transaction. Upon the transition, employees will be eligible
to make any applicable benefit elections under these plans. Following the
transaction you will be eligible to enroll in the Ascential 401(k) plan, which
includes a company match provision. Ascential will recognize past service with
Mercator for purposes of vacation accruals. Your existing 401(k) plan is
expected to be terminated immediately prior to the Transaction, which will
entitle you to roll-over your balance in that plan into, among other things, the
Ascential 401(k) plan. If you are a participant in the Mercator 1997 Employee
Stock Purchase Plan, please note that the final purchase period of that plan is
expected to end immediately prior to the closing of the Transaction, and any
contributions in the plan will then be used to acquire Mercator shares, which
will then be treated in accordance with the Transaction documents.



You will also receive a relocation package to assist with your relocation from
Connecticut to the greater Boston area. This will include an advance, upon your
request, of $100,000 to be used solely toward the down payment of a house in
connection with your relocation. This advance must be repaid, and will become
immediately due and payable upon your termination. You agree that the advance is
to be withheld from monies owed to you until it is repaid. In addition, the
package includes a payment of up to $25,000 (subject to applicable tax
withholdings and other deductions) to cover actual relocation costs for you and
your family. This also provides for reimbursement for actual and reasonable
costs associated with a reasonable number of family trips to the Boston area to
familiarize you and your family with this area and to assist you in your search
for a house. We will continue to pay for your current housing and automobile, at
the rates paid currently by Mercator, until the termination of the respective
lease on each.

In the event of involuntary termination for a reason other than cause, as cause
is defined in the Ascential Change in Control Agreement, that occurs following
December 31, 2005, we will cover up to $50,000 (subject to applicable tax
withholdings and other deductions) of the actual and reasonable costs associated
with your move to Australia. In addition, these expenses will be borne by
Ascential only if your move out of the U.S. occurs within 180 days of
termination.

Your employment with Ascential will be "at will," which means that it is not for
any specific period of time and your employment may be terminated with or
without cause by you or Ascential at any time and for any reason. As an employee
of Ascential, you also agree to comply with company policies, procedures and
standards of conduct that may be established by Ascential.

It is a condition to the receipt of the benefits that are described herein that
you execute the following documents, in the form attached, (i) the Retention
Agreement with Ascential and Mercator Software, (ii) the Executive
Non-Competition, Non-Solicitation and Developments Agreement with Ascential and
Mercator Software and (iii) the Non-competition, Non-disclosure and Development
Agreement with Ascential, which will supercede the agreement described in clause
(ii) as of the closing of the Transaction. Please acknowledge your acceptance by
signing and dating this letter and returning both this letter and the above
listed agreements to Pamela Riordan in the Ascential Human Resources department,
50 Washington Street, Westborough, MA 01581 or to Peter Fiore, President of
Ascential. In addition, you must complete and sign the attached W-4 and I-9
prior to your first day of employment and your immigration status must be
appropriate for you employment by Ascential. We will assist you with any
required transfer process. In the event that the Transaction does not occur,
this letter agreement and the above listed documents will be null and void and
of no force or effect.

Mark, we are very excited at the prospect of you joining our team. I'm confident
that as a team, we will build our company into the success and source of pride
we want for ourselves, our employees, our customers and our shareholders.

Best Regards,

/s/ Pete Fiore, President

AGREED ON THE     1st               August 2003
              ______________DAY OF ______________

SIGNED: /s/ Mark Register
       ____________________________________________

                                       2



                       NON-COMPETITION, NON-DISCLOSURE AND
                             DEVELOPMENTS AGREEMENT

In consideration of my employment by Ascential Software Corporation or any of
its subsidiaries existing currently or in the future, including Mercator
Software, Inc. (together, the "Company"), or my continued employment at will by
the Company, the payment to me of the salary or other compensation that I will
receive during my employment and the receipt by me of the other compensation and
benefits described in the letter agreement between myself and the Company of
even date herewith, I agree as follows:

1.       I shall not, either during or after my employment, disclose to anyone
outside the Company, or use other than for the purpose of the business of the
Company, any Confidential Information of the Company or any information received
in confidence by the Company from any third party of which I become aware during
my employment with the Company. "Confidential Information" means information and
data, whether in oral, written, graphic, or machine-readable form, relating to
the Company's or a third party's past, present or future business, including,
but not limited to, computer programs, routines, source code, object code,
firmware, data, information, documentation, know-how, technology, designs,
procedures, works of authorship, business plans, formulas, discoveries,
inventions, trade secrets, improvements, concepts, ideas, product plans,
research and development, personnel information, financial information, customer
lists and marketing programs and including, without limitation, all documents
marked as confidential or proprietary and/or containing such information, which
the Company has acquired or developed and which has not been made publicly
available by the Company. I further understand that Confidential Information
does not include any of the foregoing items that have become publicly known or
made generally available through no wrongful act of mine.

2.       I shall not disclose to the Company, use in the Company's business, or
cause the Company to use, any information or material which is confidential to
any third party unless the Company has a written agreement with such third party
allowing the Company to receive and use such information or materials. I will
not incorporate into my work any material that is subject to the proprietary
rights of any third party, unless the Company has the right to incorporate such
material. Notwithstanding the foregoing, I hereby warrant and represent to the
Company that I have no obligations, by reason of prior employment relationships
or otherwise, which might in any way affect my ability to give my best efforts
to the present or future business of the Company or to carry out the provisions
of this Agreement, including the assignment of rights contemplated herein.

3.       I agree that during my employment with the Company I will not engage in
other employment, occupation, consulting or other activity relating to the past,
present or future business in which the Company is now or may hereafter become
engaged, or which would otherwise conflict with my obligations to the Company.
If I leave the employ of the Company for any reason whatsoever, I shall return
to the Company all property of the Company or of any third party provided to the
Company, including all copies thereof and including, without limitation,
Confidential Information such as drawings, computer programs, and documentation
(on electronic media or on printouts), notebooks, reports, and other documents.

4.       I agree that during my employment with the Company and for twelve (12)
months following termination of my employment with the Company for any reason
whatsoever or for no reason, I will not, directly or indirectly: (i) recruit,
solicit or induce, or attempt to induce, any employee of or consultant to the
Company to terminate his/her employment with, or otherwise cease any
relationship with, the Company; (ii) solicit, divert or take away, or attempt to
divert or take away, any business of any of the clients, customers or accounts
or prospective clients, customers or accounts of the Company with respect to any
products and services of the Company which were contacted, solicited or served
by the Company at any time during the twelve (12) month period preceding the
termination of my employment or (iii) as an individual, proprietor, partner,
stockholder, officer, employee, director, consultant, joint venturer, investor,
lender, or in any other capacity whatsoever (except as the passive holder of not
more than one percent of the



total outstanding stock of a publicly-held company), engage anywhere in the
world in the business of developing, producing, marketing or selling products or
services similar to or competitive with any kind or type of products or services
which were conceived, developed, produced, marketed or sold by the Company or
any of its affiliates while I was employed by, under a consulting relationship
with or otherwise associated with the Company or any of its respective
affiliates including Mercator Software, Inc, and/or those that engage in the
development and/or marketing of software infrastructure products that have the
purpose or may be used, with or without adaptation or modification, to primarily
address requirements or functionality that can be characterized as primarily
related to infrastructure or data integration, enterprise and any other
application integration, extraction transformation and loading (also commonly
called ETL), data quality, cleansing and/or integrity and/ or business process
integrations. I agree that the competitive entities described in clause (iii) of
the preceding sentence include (but are not limited to) WebMethods, Informatica,
SeeBeyond, FirstLogic, Vitria, TIBCO, SONIC, IBM Data Management and WBI groups,
BEA, Versata, SAP, SAS, BusinessObjects, Ab Initio, IONA, iWay and MetaMatrix.
If any restriction set forth in this Paragraph 4 is found by any court to be
unenforceable because it extends for too long a period of time, or over too
great a range of activities, or over too broad a geographic area, I agree that
the restriction shall be interpreted to extend only over the maximum period of
time, range of activities, or geographic area which the court finds to be
enforceable. I acknowledge that the restrictions contained in this paragraph 4
are necessary for the protection of the business and goodwill of the Company and
are considered by me to be reasonable for such purpose.

5.       I hereby assign to the Company my entire right, title and interest in
all Developments worldwide, together with the goodwill associated therewith,
including all patent rights, trade secret rights, trademarks, copyrights, rights
of publicity, rights of privacy, and other proprietary rights, including the
right to sue for past infringement of any such rights. "Developments" means any
idea, invention, method, process, design of a useful article (whether the design
is ornamental or otherwise), computer program, including source code, firmware
and object code and related documentation, trademark, service mark, design,
logo, and any other work of authorship, or audio/visual work, heretofore or
hereafter written, made or conceived solely or jointly by me, during my
employment (including prior to my execution of this Agreement), whether or not
patentable, subject to copyright or susceptible to other forms of protection,
including any and all tangible embodiments of the foregoing, that:

         (a)      relate to the actual or anticipated businesses or research or
development of the Company;

         (b)      are suggested by or result from any task assigned to me or
work performed by me for or on behalf of the Company, whether or not during
business hours; or

         (c)      were developed using any amount of the Company's equipment,
supplies, facilities or Confidential Information.

I acknowledge that the copyrights in Developments created by me in the scope of
my employment belong to the Company by operation of law, or may belong to a
customer of the Company pursuant to a contract between the Company and such
customer.

Items not assigned by this Paragraph 5 are listed and described on the "Schedule
of Separate Works" attached hereto as Exhibit A and are hereinafter referred to
collectively as "Separate Works."

6.       In connection with any of the Developments assigned by Paragraph 5:

         (a)      I agree to promptly disclose them to the Company; and

         (b)      I agree, on the request of the Company to promptly execute
separate written assignments to the Company and do all things deemed reasonably
necessary by the Company to enable the Company to

                                       2



secure patents, register copyrights, register marks, or obtain any other forms
of protection for Developments in the United States and in other countries.

In the event that I am no longer employed by the Company, I shall be reasonably
compensated for time spent at the Company's request to perform my obligations
under this paragraph 6.

In the event the Company is unable, after reasonable effort, to secure my
signature on any documents relating to patents, trademarks, copyrights or other
analogous protection relating to a Development, whether because of my physical
or mental incapacity or for any other reason whatsoever, I hereby irrevocably
designate and appoint the Company and its duly authorized officers and agents as
my agents and attorneys-in-fact, to act for and in my behalf and stead to
execute and file any such application or applications and to do all other
lawfully permitted acts to further the prosecution and issuance of patents,
trademarks, copyrights or other analogous protection thereon with the same legal
force and effect as if executed by me.

7.       If in the course of my employment with the Company, I incorporate into
any invention, improvement, development, product, copyrightable work or trade
secret (collectively, "Products") any Separate Works, the Company shall have,
and is hereby granted, a nonexclusive, royalty-free, fully paid-up, assignable,
irrevocable, perpetual, worldwide license, including the right to grant
sublicenses, to make, have made, modify, use, import, market, distribute, sell,
copy and prepare derivative works of such Separate Works as part of or in
connection with such Products.

8.       The Company, its subsidiaries, licensees, successors and assigns
(direct or indirect), are not required to designate me as the inventor or author
of any Development, when such Development is distributed publicly or otherwise.
I waive and release, to the extent permitted by law, all my rights to such
designation and any rights concerning future modifications of such Developments.

9.       I understand that this Agreement does not create an obligation on the
Company or any other person to continue my employment.

10.      I acknowledge and agree that the Company may, in order to protect its
interests, send a copy of this Agreement to any of my future employers.

11.      Rights and assignments granted by me in this Agreement are assignable
by the Company and are for the benefit of the successors and assigns of the
Company. My obligations under this Agreement shall survive the termination of my
employment by the Company regardless of the manner of such termination and shall
be binding upon my heirs, executors, administrators and other legal
representatives.

12.      I acknowledge that any breach by me of my obligations under this
Agreement would result in irreparable injury to the Company. The Company shall,
therefore, be entitled, without restricting the Company from other legal and
equitable remedies, to injunctive and other equitable relief to prevent or
restrain the breach of this Agreement and, to the extent permissible under
applicable law, to withhold compensation and benefits from me if I fail to
comply with this Agreement.

13.      I hereby acknowledge that the Company is now and may hereafter be
subject to non-disclosure or confidentiality agreements with third persons
pursuant to which the Company must protect or refrain from use of proprietary
information that is the property of such third persons. I hereby agree to be
bound by the terms of such agreements in the event I have access to the
proprietary information protected thereunder to the same extent as if I was an
original individual signatory thereto.

14.      No delay or omission by the Company in exercising any right under this
Agreement will operate as a waiver of that or any other right; a waiver or
consent given by the Company on any one occasion is effective only in that
instance and will not be construed as a bar to or waiver of any right on any
other occasion.

                                       3



15.      This Agreement constitutes the entire agreement between me and the
Company with respect to the subject matter hereof and merges all prior and
contemporaneous discussions, communications and agreements, whether written or
oral, as to such subject matter. Without limiting the generality of the
foregoing, I acknowledge that, as of the closing of the merger involving
Mercator Software, Inc. and Ascential Software Corporation, this Agreement shall
supercede and replace the Executive Non-Competition, Non-Solicitation and
Developments Agreement among myself, Ascential and Mercator Software, Inc. This
Agreement may only be amended by a writing signed by both me and the Company.

16.      In the event any paragraph or provision of this Agreement shall be held
to be illegal or unenforceable, such paragraph or provision shall be modified to
the extent necessary to be found legal and enforceable and the entire Agreement
shall not fail on account thereof, but shall otherwise remain in full force and
effect. This Agreement may be signed in two or more counterparts, each of which
shall be deemed an original and all of which shall together constitute one
agreement.

17.      This Agreement shall be governed by the laws of the Commonwealth of
Massachusetts, without regard to its conflicts of law provisions.

18.      I acknowledge receipt of a copy of this Agreement.

[Remainder of Page Intentionally Left Blank
Signature Page Follows Immediately]

                                       4



IN WITNESS WHEREOF, I have hereunto set my hand and seal on the dates referenced
below.

/s/ Mark W. Register
____________________________________
Employee's Signature

Mark W. Register
____________________________________
Employee's Full Name (Print)

8/1/03
____________________________________
Date

Accepted by:

ASCENTIAL SOFTWARE CORPORATION

/s/
____________________________________
Authorized Officer's Signature
____________________________________
Title
____________________________________
Date

                                       5



                                    EXHIBIT A

SCHEDULE OF SEPARATE WORKS

The following are works in which I have any right, title or interest, and which
were conceived or written either wholly or in part by me, prior to my employment
by the Company and are not being assigned by me to the Company.

Description:  (if none, enter the word "None")

none
____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

Please indicate if any item listed above has been published, registered as a
copyright, or is or has been the subject of a patent application:

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

Please indicate the name of any organization or third party who also has rights
in any of the listed items. (Such as former employers, partners, etc.)

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

The foregoing is complete and accurate to the best of my knowledge.

/s/ Mark W. Register
____________________________________
Employee's Signature

    Mark W. Register
____________________________________
Employee's Full Name (Print)

    8/1/03
____________________________________
Date