The W3C HTML Data Task Force has published two notes, the HTML Data Guide and Microdata to RDF. According to the abstract of the former, " This guide aims to help publishers and consumers of HTML data use it well. With several syntaxes and vocabularies to choose from, it provides guidance about how to decide which meets the publisher's or consumer's needs. It discusses when it is necessary to mix syntaxes and vocabularies and how to publish and consume data that uses multiple formats. It describes how to create vocabularies that can be used in multiple syntaxes and general best practices about the publication and consumption of HTML data."
The Microdata to RDF note states, "HTML microdata [MICRODATA] is an extension to HTML used to embed machine-readable data into HTML documents. Whereas the microdata specification describes a means of markup, the output format is JSON. This specification describes processing rules that may be used to extract RDF [RDF-CONCEPTS] from an HTML document containing microdata."
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