Well, essentially, most SOAP transfer is merely an HTTP request, but "the devil is in the details", in terms of how the server listens for the structure of the requests and formats the data in the response. If all you want to return is a simple integer, no big deal. If you want to return a multidimensional table, you'll have to figure out how to format the data so that the rows and columns are properly delimited (and don't forget to escape and unescape the delimiters in the actual data!).

SOAP defines common ways to serialize the data, in such a way that it can be implemented in many languages. Also, SOAP can be proxied using other technologies (SOAP over email for example). I wrote an article for apple.com about using SOAP to bridge between Perl and AppleScript, passing structured data (a hash in Perl became a record in AppleScript... transparently). That was cool, and effortless.

SOAP is just glue. But a good glue, and multi-vendor supported. It's great that Perl has good support as well.

-- Randal L. Schwartz, Perl hacker
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