AsiaInfo Technologies (China) Inc. AsiaInfo Technologies (China) Inc. AsiaInfo Technologies (China) Inc. AsiaInfo Technologies (China) Inc. This document specifies a normative semantic layer for agent-to-agent interaction in the Internet of Agents (IoA). The semantic layer provides a common ontology model and a JSON-LD serialization profile (RECOMMENDED), while allowing other RDF serializations for expressing capabilities, intents, tasks, and context. The document defines required classes and properties, a negotiation procedure, and alignment rules for heterogeneous ontologies. This layer is designed to be used by interaction and discovery protocols but does not define transport, session, or security protocols. It enables deterministic semantic interoperability across domains.