My goal is to explain the types of tools you'll probably need and to point you to likely candidates.
You'll still need to research, test, and compare tool features against your project needs to assemble your ultimate toolbox.
Trial versions (with time-limits or with key features disabled) are usually available for download and evaluation.
All four restrict using their name in a derived product without permission.
Once you have a DTD or schema and the XML document to go with it, you'll need a parser to read and interpret the XML document.
The data may be exchanged in the form of application files in XML format, or over network connections that exist only for a moment before being discarded at the conclusion of an online transaction or at the close of a network connection.
Also, this isn't a comparative review that rates tools.
Also, I'll leave the more detailed explanations of XML to the background sources in Related topics.