can any one help me to develop a function which generates an xml file from a temp-table (as a paramer of the function)
If you get a buffer handle to the temp table I believe there is a function on the buffer handle object called "WRITE-XML". Check it out in the keyword help.
Progress has built-in functions for reading and writing both XML and JSON.
Here is a link for WRITE-XML() documentation. It also has couple of examples at the end.
Depending on the info you want to export from the temp-table you can use the info from the following OpenEdge documentation of "Working with XML":