Layers

[mark.reinhold at oracle.com]

2015/9/9 1:48 -0700, david.lloyd at redhat.com:
> ...
> 
> 4) Layers
> 
> I am concerned that layers do not go far enough to ensure that different 
> module graphs can interoperate.  There is seemingly no provision to 
> establish dependency relationships between modules in different layers, 
> because layers are apparently strictly hierarchical.

True -- a module in one layer can only depend upon modules in that layer
or in lower layers.

>                                                       This would make it 
> much more difficult to (for example) allow different containers to 
> interoperate within an app server (OSGi and Java EE, for example). 
> Today we use this kind of relatability to allow Java EE modules to 
> depend on modules constructed out of the legacy extensions system as 
> well as filesystem-backed JARs which are modularized independently of 
> our Java EE container, allowing them to be reused from other containers 
> as well.

The goal of layers is not to allow completely different containers (or
module systems) to interoperate, but rather to satisfy the "dynamic
configuration" requirements previously discussed.

- Mark