Thanks for your help so far. Let me give you some actual data so that it will be easy to interpret.

ROOT          OBJECT        KEY      COLUMN   OLD        NEW
EMPLOYEE      EMPLOYEE      XYZ      TITLE    <null>      Mr    
EMPLOYEE      EMPDETAILS    DEF      CITY    California  New York    
CUSTOMER      CUSTOMER      ABC      CAPTION  Regular    Premium
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File 2

EMPLOYEE    EMPLOYEE    NEW EMPLOYEE 1
EMPLOYEE    EMPLOYEE    NEW EMPLOYEE 9
EMPLOYEE    EMPDETAILS    NEW EMPLOYEE1-DETAILS
EMPLOYEE    EMPDETAILS    NEW EMPLOYEE9-DETAILS
EMPLOYEE    EMPDETAILS    NEW EMPLOYEE16-DETAILS
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File 3

EMPLOYEE    EMPLOYEE    NEW EMPLOYEE 6
EMPLOYEE    EMPDETAILS    NEW EMPLOYEE6-DETAILS
CUSTOMER    CUSTOMER    NEW CUSTOMER
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So from these three files i wrote small perl program to generate the files in xml

<Data>
    <EMPLOYEE>
        <KEY name = 'XYZ'>
            <TITLE>
                <oldvalue></oldvalue>
                <newvalue>Mr</newvalue>
            </TITLE>
        </KEY>
    </EMPLOYEE>
    <EMPDETAILS>
        <KEY name = 'DEF'>
            <CITY>
                <oldvalue>California</oldvalue>
                <newvalue>New York</newvalue>
            </CITY>
        </KEY>
    </EMPDETAILS>
    <CUSTOMER>
        <KEY name = 'ABC'>
            <CAPTION>
                <oldvalue>Regular</oldvalue>
                <newvalue>Premium</newvalue>
            </CAPTION>
        </KEY>
    </CUSTOMER>
</Data>
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Output 2

<Data>
    <EMPLOYEE>
        <KEY>'NEW EMPLOYEE 1'</KEY>
        <KEY>'NEW EMPLOYEE 9'</KEY>
    </EMPLOYEE>
    <EMPDETAILS>
        <KEY>'NEW EMPLOYEE1-DETAILS'</KEY>
        <KEY>'NEW EMPLOYEE9-DETAILS'</KEY>
        <KEY>'NEW EMPLOYEE16-DETAILS'</KEY>
    </EMPDETAILS>
</Data>
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Output 3

<Data>
    <EMPLOYEE>
        <KEY>'NEW EMPLOYEE 6'</KEY>
    </EMPLOYEE>
    <EMPDETAILS>
        <KEY>'NEW EMPLOYEE6-DETAILS'</KEY>
    </EMPDETAILS>
    <CUSTOMER>
        <KEY>'NEW CUSTOMER'</KEY>
    </CUSTOMER>    
</Data>
[download]

Now i need to combine all these three into single output file. First field tells the root object. So for EMPLOYEE, i need to display details of EMPLOYEE and EMPDETAILS table what has been in one db, other db, and if exists in both db what are the old and new values (these all are created from perl program and it contains only delta information). Similary for CUSTOMER root object, i need to display all entities of this object and then what exists in one db,other db, modified information. There are many occurances of modified columns i.e. for each key several columns can be modified

There are no headers in any file. I have added one in first input for clarification