RDF
The Resource Description Framework (RDF) is a standard model for data interchange on the Web. It is the foundational data structure of the semantic-web.
RDF facilitates data merging even if the underlying schemas differ, and it specifically supports the evolution of schemas over time without requiring all the data consumers to be changed.
RDF extends the linking structure of the Web to use URIs to name the relationship between things as well as the two ends of the link (this is usually referred to as a "triple": subject-predicate-object).