Specify the elements, categories or fields into which data is to be divided; whether they are required, optional or prohibited; and the order in which they must appear.

• Australian Government Locator Service (AGLS) Metadata Standard
• Data Documentation Initiative (DDI) - project to develop an XML document type definition for data documentation
• Developing Common Standards - Metadata Scheme for Websites in the Legal and Advice Sectors - November 2000
• DocBook - SGML DTD maintained by the DocBook Technical Committee of OASIS, particularly suited, though not limited, to books and papers about computer hardware and software
• DocBook: The Definitive Guide - book available online, Norman Walsh and Leonard Muellner, 1999
• DocBook XML Schema - Sun Microsystems
• Eurpoean Chronicles Online (ECHO) Metadata Model - metadata elements to better describe film information as well as automating the metadata analysis
• Global Information Locator Service (GILS)
• HL7 Reference Information Model - used in the medical community
• MAchine Readable Cataloging (MARC) - standard for bibliographic data
• Cataloging Electronic Resources: OCLC-MARC Coding Guidelines - intended to assist catalogers in creating records for electronic resources in WorldCat, the OCLC Online Union Catalog, December 2001
• MARC 21 XML Schema - framework for working with MARC data in an XML environment, includes schemas, stylesheets and software tools
• Mathematical Markup Language (MathML), Version 1.01 - (W3C Recommendation) XML application for describing mathematical notation and capturing both its structure and content, in order to enable mathematics to be served, received, and processed on the World Wide Web, just as HTML has enabled this functionality for text
• Mathematical Markup Language (MathML), Version 2.0 - (W3C Recommendation) XML application for describing mathematical notation and capturing both its structure and content, in order to enable mathematics to be served, received, and processed on the World Wide Web, just as HTML has enabled this functionality for text
• Structure for the identification of organizations and organization parts (ISO 6523) - standarized set of fields for the description of organizations
• Text Encoding for Interchange (TEI)
• Guidelines for Electronic Text Encoding and Interchange (TEI P3) - based on encoding in SGML
• Guidelines for Electronic Text Encoding and Interchange (TEI P4) - corrects numerous errors in P3 and provides a preliminary XML-compliant version
• Text Encoding Initiative
• Web Services Description Language (WSDL) Version 2.0 - defines the core language which can be used to describe Web services based on an abstract model of what the service offers
• Web Services Description Language (WSDL) Version 1.2: Bindings - (W3C Working Draft as of 2002-07-19) describes how to use WSDL in conjunction with SOAP 1.2, HTTP/1.1 GET/POST and MIME
• XFrames - (W3C Working Draft as of 2002-08-20) replacing HTML frames, XFrames is an XML application for composing documents together that makes the content of framesets visible in their URIs
• XML Bookmark Exchange Language (XBEL) - interchange format for bookmark data as used by most Internet browsers, 1998