5. A non-transitory machine readable medium storing one or more sequences of instructions for enabling a system to transform XML (eXtensible Markup Language) data and data from an external source to a combined output in a desired format, wherein execution of said one or more instructions by one or more processors contained in said system enables said system to perform the actions of: receiving a XML data, said XML data containing a plurality of elements; accessing configuration data specifying a plurality of context objects, wherein a first context object of said plurality of context objects is enabled to interface with said external source; retrieving a set of XSL (EXtensible Stylesheet Language) transformation rules, wherein each of said set of XSL transformation rules specifies a respective portion of said combined output to be generated based on one or more of said plurality of elements, wherein a first XSL transformation rule of said set of XSL transformation rules specifies, for a first element, that said first context object is to be used to generate a first output portion; parsing said XML data to identify the occurrence of said first element; in response to the occurrence of said first element, invoking said first context object, which in turn retrieves a first data from said external source; forming said first output portion by incorporating said first data according to said first XSL transformation rule; and including said first output portion in said desired format in said output, as a response to occurrence of said first element in said XML data.
5. A non-transitory machine readable medium storing one or more sequences of instructions for enabling a system to transform XML (eXtensible Markup Language) data and data from an external source to a combined output in a desired format, wherein execution of said one or more instructions by one or more processors contained in said system enables said system to perform the actions of: receiving a XML data, said XML data containing a plurality of elements; accessing configuration data specifying a plurality of context objects, wherein a first context object of said plurality of context objects is enabled to interface with said external source; retrieving a set of XSL (EXtensible Stylesheet Language) transformation rules, wherein each of said set of XSL transformation rules specifies a respective portion of said combined output to be generated based on one or more of said plurality of elements, wherein a first XSL transformation rule of said set of XSL transformation rules specifies, for a first element, that said first context object is to be used to generate a first output portion; parsing said XML data to identify the occurrence of said first element; in response to the occurrence of said first element, invoking said first context object, which in turn retrieves a first data from said external source; forming said first output portion by incorporating said first data according to said first XSL transformation rule; and including said first output portion in said desired format in said output, as a response to occurrence of said first element in said XML data. 6. The machine readable medium of claim 5 , wherein said configuration data further specifies for said first context object respective values for a set of parameters, wherein said first context object upon invocation uses the respective values for said set of parameters to interface with said external source and to retrieve said first data.