Before XML we had CORBA, and before that EDI, and before that ASN.1... Just reinventing the wheel and each time a little worse.
For example (AFAIK) XML webservices tend to be less tightly coupled than CORBA's IDLs (though you can tight-couple in any language):
- XML using its own format specification language (DTD; XML Schema) helps keep the external data format independent from the application's internal data structures (until some bright spark realizes they can avoid duplication! by deriving one from the other... thus re-coupling them. Because of this, SOAP is CORBA all over again).
CORBA's IDL produced an interface for every object. This is fine for methods of the top-level object (that represents the main actions of the application/service), but when applied to objects that form the internal data structures (the nested object tree/graph that is received/sent as an argument/return value), it forces the external format to have the same structure as the internal data structure, thus tightly-coupling them. [And, CORBA tried to do "distributed objects", which just didn't work very well - though it sounds like a good idea.]
REST seems to be making a big difference. It explicitly uses "representational state", meaning that the external format is independent of the sender and receiver's internal representation. By defining the format independently of an end-point, it seems you escape tight-coupling. In practice, devs will often derive internal object definitions from the external format - but then they do the loose-coupling themselves, internally, and so tight-coupling is still avoid. [It's seeming to me that deriving internal-->external is bad; but external-->internal is OK.]
In a way, I think this progression can be seen as realizing the concept of information hiding in greater and greater depth as time goes on.
Does that seem right? What do you think? Can you point me to any references that address these issues (esp about tight-coupling between internal/external representations)? Many thanks for any help!
I don't disagree with you about bloated middleware products, but you don't have to use them to use soap,xsd,xsl,xpath etc.