specified set of methods on remote resources. Protocols: HTTP, gRPC is also possible for Resource Tunnel Idea: Call a procedure/command on a remote server as you would locally call a function in your programming language. Protocols: SOAP, XML/JSON-RPC, gRPC Query Idea: Formulate a query against a remote dataset as if the API were a database (cf. SQL). Protocols: HTTP (Query), GraphQL Event-Based Idea: Fetch events coming from a message broker Protocols: AMQP, MQTT, CloudEvents