DIY Schema Validation for Workmanlike ONIX

...

There is a lovely generic XML software product called XML Notepad 2007. It's free and written by a Microsoft programmer, Chris Lovett, so the freeware is from a safe source, it's easy to set-up for a schema validation and robust with files as large as 20,000 records.  Not surprisingly it only works with Windows operating systems.  The software requires that you have.NET Frameworks verson 2.0 or above installed version 4.0 installed  (note that .NET is likely already on your computer, but it's another Microsoft product and safe if you need to download it.). http The download site has moved about recently, but as of 2016 Lovett was still updating it.  The current site, now offering clone or download is here:

https://www.codeplexgithub.com/xmlnotepadMicrosoft/XmlNotepad

MAC

There are fewer free choice for Macs, but there is a good one that only costs $1.99 at the Mac App Store – XML Nanny:

...

XML Nanny is excellent, simple software but some users have reported a line limit on XML Nanny where the software reports an error at line 65,535 when the actual error is many lines further down the file.  It appears that citation is accurate – an error exists – but the line reporting stops working.  If XML Nanny reports the file is fine, it is.  It's only if it reports an error after line 65,535 that this crops up.  On the assumption working solution to an issue is better than nothing and that you might have access to a PC, if you think you've encountered this issue and need a workaround try ONIX file splitter:

Free ONIXEdit Splitter

It's excellent software and reliably splits any size of ONIX file of either version, into same sized pieces which can be individually validated if you think you've run into this issue.

Linux and MAC

xmllint comes installed in most Linux versions and on many Macs as well.  It's a command line XML parser which means you'll need to write small scripts to do validations. I'm not going to illustrate any more than the below (and don't use this unless you're more comfortable using command line tools than me), but this example is intended for a Mac, with the username "Bob" with a folder called "schema" on his "Desktop", containing (in this case) the ONIX 2.1 reference schema "ONIX_BookProduct_Release2.1_reference.xsd",  The Desktop contains an ONIX file "TestOnix.xml" which has been set up for schema as noted below.  

Note that there are some instructions in the "Reference or Short Tag" section below on how to confirm the file location on a MAC – you have to be absolutely right in your location or it doesn't work. And you need to understand the difference between Reference or Short tags as well.  All that is discussed below in more detail.

This worked for me using Terminal:

xmllint --schema /Users/Bob/Desktop/schema/ONIX_BookProduct_Release2.1_reference.xsd /Users/Bob/Desktop/TestOnix.xml

You can find a full listing of commands here:

Java

Java based programs should workon any system but are seldom free.  I'll illustrate oXygen as it's often recommended for working with ePub.  It's expensive but you can get it on a 30 day trial.  Any of the versions Editor / Developer / Author will work for validation.

...