Ascential open source is a "dual use" kind of license. Basically means Ascential can do what it wants with the software including offer commercial terms, for everyone else it's like the GPL with the additional requirement that any mods you make to the software are relicensed back to Ascential. There are other licenses like this e.g., mySql and cygwin, I'm told there are others as well.

This particular implementation is not intended to be production quality so I'm not sure the commercial terms matter in the above license. This implementation is being designed from the ground up to be simple, clear, and easily modified so that as we iron out the exact semantics of DFDL we can do so with a real implementation. These goals are in tension with performance, which we're punting on entirely. So, for example, almost all the Java object classes in this implementation are immutable objects. This makes the code dead-simple, but implies lots of object allocation and garbage collection during execution. We expect several objects to be allocated and discarded for every bit of input that is touched when reading data, for example.

The GGF doesn't do "reference implementations", so I'm calling this thing an "Informational Implementation", but the spirit is the same. Our DFDL spec documents can be far clearer if we have an implementation that is easy and quick to modify, and one we can run real tests against readily as we debate the fine points.Our goal at Ascential is for this implementation to exactly match the standard.