Historically first officially published CA Gen API was the Encyclopedia and Workstation Application Program Interface (API) software for CA Gen. It supports the Host Encyclopedia and the Client Server Encyclopedia (CSE) for all available API platforms and databases. It also supports local access to workstation models, Host Encyclopedia, and the CSE for all available API platforms and databases.
The Encyclopedia API is a set of C functions, include files, and libraries. You must be familiar with the C programming language and the software development tools for the platform on which you are working in order to use the Encyclopedia API. You must also be familiar with the CA Gen meta-model.
Today we have CA Gen JMMI API written in Java. The JMMI was introduced when CA Technologies announced the CA Gen Studio built on the Eclipse platform. The JMMI is frontend written in Java, but most of their methods are native methods written in C++. The JMMI does not offer access to the models stored in one of the supported encyclopedias (HE and CSE). Therefore, the Encyclopedia API is the only way to access models stored in the HE and CSE.
The JGen Notes Core Java project is offering Java wrapping for the models located on the workstation only (limitations of the CA Gen Free Gen), but those interfaces can be easily extending to the model located in the remote places like Client Server Encyclopedia (CSE) or Host Encylopedia (HE).
You can find sources of the implementation here and here.