I'd ask you to reformulate the question. What are you trying to do?
If you want to run an interview through a Chat client, then the Chat API (REST) will be for you.
If you want to integrate OPA into a CX or ERP, then either the Connector Framework (SOAP) or the Generic Connector (REST) will be the right choice.
If you want to construct a completely new interview experience but keep the metadata of the Screens and Controls in OPA, then the Interview Service (SOAP) is for you.
If you want interview-less services, then Assess (SOAP) or Batch Assess (REST) are your options.
And there are others.
But to answer your question, it would help to know what are you trying to do?
Great summary, Richard!
Word of warning on the Interview Service though... The Interview Service is not recommended for new projects. See the following note from the documentation (Create your own interview experience -- emphasis added):
"Note: The interview service does not support the inherently dynamic style of interactions in Latest Version interviews (type into a control and the screen will respond as needed almost immediately). While the interview service can be used for Latest Version interviews, it was designed for use with August 2016 style interviews, where data on a screen is collected, then explicitly submitted by the user to find out if it is OK to proceed to the next screen. For new projects where custom interview appearance and behavior is needed, the recommended approach is to use interviews embedded directly into a web page, and interview extensions. Future functionality and controls will likely not be made available in the interview service, whereas they will be made available in embeddable interviews and interview extensions."
Thanks for the reminder in respect of the Interview service. Let's see what the OP response is!
It was just a general query where wanted to understand REST API use cases and your summary sums it all and it is very useful.
Thanks for the reply.
Siddeeq Basha Y K