Schema.org is a collaborative, community activity with a mission to create, maintain, and promote schemas for structured data on the Internet, on web pages, in email messages, and beyond.

Schema.org vocabulary can be used with many different encodings, including RDFa, Microdata and JSON-LD. These vocabularies cover entities, relationships between entities and actions, and can easily be extended through a well-documented extension model. Over 10 million sites use Schema.org to markup their web pages and email messages. Many applications from Google, Microsoft, Pinterest, Yandex and others already use these vocabularies to power rich, extensible experiences.

Protocol Buffers are language-neutral, platform-neutral extensible mechanisms for serializing structured data.

• Protocol Buffers @ GitHub.
• Protocol Buffer Design: Principles and Practices for Collaborative Development @ Lyft Engineering's Medium.