We have many *many* dependencies from Daffodil, and this has the potential to cause conflicts when creating systems that use Daffodil as part of a larger system.
If an application requires libraries A and B (suppose B is daffodil), and those each in turn require library C (suppose C is the ICU libraries), but A and B each depend on different incompatible versions of C, then you have an unresolvable conflict. This is called the "dependency isolation" problem. One would like to be able to link libraries A and B with their own respective isolated versions of library C, with no interactions. In the past I had examined the OGSI modular components system (used by Eclipse) and rejected it for excess complexity. OGSI solves the dependency isolation problem, but it also introduces a lot of additional long-running software system lifecycle mechanism that is quite complex, and not well motivated for a library like Daffodil. I had hoped that the Java 9 modules stuff would be a rethink on all of this, and that it would be focused on solving only selective linking (leaving out what you don't use), and dependency isolation. What I have learned is that Java 9 modules does half of what I wanted. It successfully allows selective linking and has been used to modularize the gigantic Java runtime to enable smaller footprint in memory. That much is good. But the Java 9 modules system does *not* solve the dependency isolation problem. There can still only be one copy of each library version for all dependencies of all modules. I would include references, but a web search for Java 9 Modules OGSI gets you many hits and you can find the discussions easily. Tools like scala-steward don't eliminate the need for dependency isolation, but they do minimize it, especially for open-source software. People who are building systems combining large libraries like Daffodil with commercial slow-changing software libraries having dependencies on older versions of many other things, those are the people who really run into the need for a dependency isolation solution. For the time being they will have to continue to rely on running incompatible things in separate processes or containers or using OGSI if they want everything in the same process/JVM. Mike Beckerle | Principal Engineer [cid:61c182a7-6d2e-4f39-98e0-cb25ac62333c] mbecke...@owlcyberdefense.com<mailto:bhum...@owlcyberdefense.com> P +1-781-330-0412
