xml tools
http://www.freeformatter.com/xml-validator-xsd.html – online tool for validating an xml file against an xsd
http://www.validome.org/grammar/validate/ – online xsd and dtd validator
http://www.xmlforasp.net/CodeBank/System_Xml_Schema/BuildSchema/BuildXMLSchema.aspx – online xsd generator
in linux, i was able to generate a DTD from an xml file by using the trang utility.