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▪ The Web is the most successful software application on the planet (with the possible ex-
ception of email). It is therefore general enough, with sufficient clarity and definition, to
create robust and scalable applications according to a particular style (a style whose inter-
face generally includes the methods provided by HTTP).
▪ Developers love complexity. They approach complex problems with complex solutions,
though it is a fallacy to think one is required to do so. In other words, posit a thing that is
the simplest possible thing that works; this is the best thing. REST is simpler than SOAP
and represents a small, incremental set of constraints over the Web, which are widely un-
derstood. SOAP, on the other hand, is new and different, making it harder to adopt.
▪ SOAP-based web services are hard, which often translates to “needlessly complex.”
In general, people who write topic about SOAP take an attitude of refusing to weigh in on
the matter. They point to the debate, but then don't make a statement regarding their personal
view.
On the other hand, proponents of REST tend to be very vocal regarding their preference.
The popular O'Reilly book RESTfulWebServicesby Leonard Richardson and Sam Ruby
(
http://oreilly.com/catalog/9780596529260
)
describes SOAP-based systems as “Big Web Ser-
vices.” Ruby on Rails founder David Heinemeier Hansson has termed the WS-* specifications
“WS-Death Star,” and recently pulled the SOAP libraries from within Rails and replaced them
with REST libraries.
For their part, SOAP developers refer to the other side as “RESTafarians,” in an apparent ef-
fort to reduce their simple web interface predilections to the status of hippy-dippy tomfoolery.
It's an exciting time to be in the software business!
RESTful web services are a perfectly acceptable way to build your SOA (though some REST
proponents might not even like to hear the word SOA). However, SOAP-based services are
more common at this point, probably because the big software stack vendors have a lot of skin
in that game. SOAP and all of the attendant WS-* specs take a long time to understand and
to implement, and many of the top software vendors were the brains behind these specifica-
tions. But then the specifications had to be implemented of course. And guess who is happy
to provide you with implementations….
I speculate that REST will grow considerably in popularity in the coming years. That's be-
cause the simplest thing that works usually does well, even if it takes a while for us to see it
given all the noise.
It's a reasonable argument, in my view, to suggest that SOAP-based web services, and in par-
ticular the WS-* stack, do little more than move the interoperability problem. Once you're
using tools like BPEL to orchestrate web services within a SOA, you become dependent in
