XML Problem - Design - Solution
Mitch Amiano, Conrad D’Cruz, Kay Ethier and Michael D. Thomas
Published by Wiley Publishing, Inc.
10475 Crosspoint Boulevard
Indianapolis, IN 46256
ISBN-13: 978-0-471-79119-5
ISBN-10: 0-471-79119-9
XML For Dummies® , 4th Edition
Lucinda Dykes and Ed Tittel
Published by Wiley Publishing, Inc.
111 River Street
Hoboken, NJ 07030-5774
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https://www.quackit.com/xml/tutorial/dtd_doctype.cfm https://stackoverflow.com/questions/8381037/cross-referencing-files-using-dtd-and-xml-only https://stackoverflow.com/questions/19931088/how-to-declare-an-attribute-with-default-value-that-can-be-omitted-in-dtd
http://www.informit.com/articles/article.aspx?p=425383&seqNum=7
https://www.codeguru.com/java/article.php/c13529/XSD-Tutorial-XML-Schemas-For-Beginners.htm
https://www.w3.org/TR/xmlschema-2/#built-in-datatypes
https://www.tutorialspoint.com/ruby/ruby_xml_xslt.htm