One of the latest SOA framework for Delphi, is our Open Source mORMot framework.
You can use interface
to define your Service contract, and access to them locally or remotely using named pipes, GDI messages, or TCP/HTTP. Your contract is defined as such on both client and server side, just like in WCF.
type
ICalculator = interface(IInvokable)
['{9A60C8ED-CEB2-4E09-87D4-4A16F496E5FE}']
function Add(n1,n2: integer): integer;
end;
It handles per-call, per-session, per-user or per-group instance live. See this sample code.
It is secure (with secure authentication at URI level), light and fast.
It uses JSON as communication (lighter than XML), and a RESTful access. It is ready to be consumed by AJAX or WCF clients (the latest after custom marshaling of the interfaces). It was optimized for speed and scalability (with advanced features like balanced custom hosting and per-interface/per-method access security).
The mORMot framework documentation has more than 800 pages, and some dedicated high-level explanation of Service Oriented Architecture design pattern in Delphi. It is integrated with a Client-Server ORM, so you have at hand all needed low-level tools to make a proper Domain-Driven application in Delphi, and other technologies.