Class comment:
I am the kernel of Pier. Several instances of myself might exist at the same time, but they all exist independently and don't share any data. I know the root structure and the persistency strategy of the whole data-model. Moreover I prevent any concurrent modifications to the model by providing a global mutex.
The Seaside Configuration interface of Pier has a drop-down box that lists all the registered kernels.
The protocol on the class side of PRKernel shows how to manage these.