A sub-report is simply a report composed of its own JRXML source and compiled in a Jasper file. Creating a sub-report is very similar to creating any other report. The margins of a sub-report are usually set to zero for sub-reports because a sub-report is meant to be a portion of a page, not an entire document. The horizontal dimension of the sub-report should be as large as the element into which it is placed in the parent report.