In contrast to content loaded from the internet, XML already existing within the application does not require to be loaded each time. This makes it a good choice for large files. It is possible to use XML files with more than 100,000 lines of content without causing any performance issues. In general, the limiting factor is the performance of the XSLT transformation rather than the size of the data source.
You can place such files under the the xml-from-application directory within the application. You can load the content of this file into the data-source: