It's funny that you mention SOAP as the "main" option. Because SOAP was a PITA untill very recently, mostly because SOAP::Lite is really a mess. But today you have very interesting solutions to SOAP in Perl that are much more mature, much less messy and much more standards-compliant.

On the other hand, SOAP is a protocol that expects a very strong and strict typing, that means you need to spec your data accordingly, which might be possible and even desired in a lot of cases, but on the other hand, writing a WSDL might be overkill for a lot of scenarios.

That being said, if you choose SOAP, I'd first recommend you writing a XML Schema describing the data that you want to transfer, then writing a WSDL describing how you're going to transfer it, then you can use the following modules to implement it:

• XML::Compile::SOAP
• Catalyst::Controller::SOAP and Catalyst::Model::SOAP if you like frameworks

But, as I said, that might be overkill for a lot of applications. SOAP is only worth the trouble when there's a need of data validation and consistency that can be documented as a XML Schema. Otherwise JSON is a great choice.