The World Wide Web Consortium released “XML Schema Second Edition” as a W3C Recommendation in three parts: “Part 0: Primer,” “Part 1: Structures” and “Part 2: Datatypes.” The second edition is not a new version; it corrects errors found in the XML Schema first edition. A modular approach well-suited to distributed applications, XML schemas define shared markup vocabularies and the structure of XML documents using those vocabularies.