For a new project, I want to use the open source version of Saxon.

However, if from Java I want to pass an object as a parameter to my XSLT transformation, do I need to purchase a commercial Saxon license?

For example, instead of having multiple xsl:param declarations that each map to an integer or string value, I would rather pass a single schema instance from Java to the XSLT transformation process.

Is there any good documentation that shows how I would then access the schema instance values from XSLT?

The basic version of Saxon (non-schema-aware, open source) allows you to use the built-in schema types such as integer, string, boolean, date, etc. It also allows you to pass an XML document, which is treated as being unvalidated and untyped.

To use user-defined types such as part-number, invoice, etc, you need the schema-aware (commercial) version.

Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference