Transactions Project
The Aries JTA project focuses on making container managed transactions available as OSGi services.
For more information, check out section "123 JTA Transaction Services Specification 1.0" in the "OSGi Service Platform Enterprise Specification, Release 4, Version 4.2" available for public download from the OSGi Alliance
Some of the aspects of working with Aries JTA are already covered in the JPA module.