I've been thinking about how we develop transactional applications for a very long time. That thought process got interrupted for a bit, but I came back to it over Christmas and recent events and articles have pushed this further. Plus we're working on transactional aspects for Drools 5 which has covered writing XAResources. Back in HP we had a tutorial on how to do this, which I think we're going to dust off and maybe Jonathan and the team will write some articles around that topic. (I know it's the subject of an update to the book, whenever that happens!)
But it got me thinking that as soon as people start asking about how they can write XAResources to make their data transactional then we really haven't progressed as an industry. XA is a good standard. But it's not perfect. (No standard is!) Plus it was designed with very specific database use cases in mind, which were fine 30 years ago but aren't always a perfect fit for the 21st century. The question should be "how do I make my data transactional?" and leave the implementation specifics to the engine or container.
We spent a great deal of time over the last 20 years making the development of transactional applications easier (HP was using Arjuna 20 years ago and liking it). Some PhD students wrote an entire database system based on it too. Simplicity, flexibility and power were keys to its success (nested transactions rule!) Back then there was little differentiation between the transaction engine and the way in which you developed applications. Subsequently we emphasized that they were different (Arjuna became known as the engine, while Transactional Objects for Java was the framework for developing applications).
However, we've not concentrated on the latter in recent years, which is a shame and something that we're going to remedy, because it's a proven way of developing flexible transactional applications. I think we'll throw in annotations and try to make it slightly less invasive than it was (back in the 1980's there was no such thing as Java let alone annotations). Hopefully we'll then be able to offer this to developers building on JBossTS and they can move away from asking "How do I write an XAResource?" to "What do my users want from my application/framework/service/..?" Leave the transaction complexity to JBossTS.
Side-note: while writing this I was reminded that we have a student project on some of these ideas, though not necessarily tied to TOJ. So if you are a student and looking for something to do, now may be the time to give it a go.