Hey Sandra, thanks for your response,
as you can see in my response to VS's answer, we are actually using the IXML library to parse the received XML and then use the information about the function module, we get from database table fupararef, to convert the strings from the XML to the correct type.
Unfortunately, we have some performance issues, which are not a big problem, when parsing an XML, but during XML creation (based on the result of the function module).
And yes, XSLT / ST is very new to me, indeed. But, as this is so much faster, than our IXML handling, my hope is, that it is possible to do the whole abap - xml transformation solely in XSLT (or ST, as it is faster - thanks for this information!). But I do not know, if it is possible to detect (in XSLT / ST), if the source object is a table or a deep structure (like I could use
DESCRIBE FIELD l_value TYPE l_type
to get the type in ABAP).