What is RDF primarily used for?

RDF, or Resource Description Framework, is primarily utilized for describing resources in the semantic web. It provides a standard model for data interchange on the web and allows for the representation of information about resources in a structured way. RDF uses a subject-predicate-object format to create statements about resources, which enables the description and linking of various types of content across different systems and platforms. This structured approach facilitates interoperability and the ability to query and reason about the data, making it essential for applications that rely on semantic understanding, such as linked data and knowledge graphs.

The other choices do not accurately reflect the main purpose of RDF; for instance, while human-readable documentation and user interface design are important aspects of web development, they do not pertain to the core functionalities of RDF. Invoicing IoT transactions relates more to financial processes rather than the semantic representation of web resources, which is the focus of RDF.