What type of API is EMI described as?

EMI, which stands for External Message Interface, is correctly classified as a PL/SQL API. This is primarily because it is designed to interact with databases using Procedural Language/Structured Query Language (PL/SQL), which is Oracle's extension of SQL that combines SQL with procedural features. The use of PL/SQL allows developers to write complex queries and procedures to manipulate data, making it an effective choice for tasks that require robust database interactions.

In contrast, the other types of APIs mentioned have distinct characteristics that set them apart. REST APIs operate over HTTP and are stateless, typically using JSON or XML for data interchange. WebSocket APIs provide a full-duplex communication channel over a single TCP connection, allowing for real-time data transfer, which is quite different from the database-focused functionality of PL/SQL. GraphQL APIs allow clients to request specific data structures, enabling efficient data retrieval but are not primarily built around PL/SQL or database interactions.

Thus, recognizing EMI as a PL/SQL API accurately reflects its purpose and functionality within the context of the Avaloq Message Interface.