what does this aggregator will do,will it only with replica,or we can aggregate different xml documenrs,want to just know in which situations it is used…

The sample application gives an example of using aggregation on Page 4 (navigate the app using Previous/Next at the bottom of the screen).

The example shows an original XML document containing a Purchase Order from Customer ID 100001. This original document is replicated, one replicant being the original Purchase Order and the other being used to get Customer Information for customer 100001 via a SOAP request. The original PO and the new Customer Information are aggregated using:

  <document rdf:ID='originaldoc' />
  <document rdf:ID='custinfo' >

in the file poaggmodel.xml (part of the posequence.xml sequence).
So in the example output document, Customer Info for name, address, city, state and zip has been added from an external (soap) source.