What don't we know from the filenames:

 - product: ? More logic needed
 - realm: from the MIP table
 - version: Must be deduced form datanode?
 - institute: Configured on ingest
 - frequency: From MIP table
 - activity: Configured on ingest


Versioning
==========

isenes.drslib is going to be where the version directory structure
tool lives.

Definitions
-----------

DRSTree: A DRS filesystem hierarchy rooted at a given path.  Each DRS
tree is associated with a set of PublisherTree.

PublisherTree: A directory containing multiple versions of a
publication-level dataset.  A PublisherTree can be in one of several states:

 1. InitialCMOR
 2. VersionedPrepublished
 3. VersionedPublished
 4. VersionedTransition


gridspec support
----------------

Gridspec files have a different syntax to DRS data files.  They are of
the form:
    
    gridspec_<realm>_fx_<model>_<experiment>_r0i0p0.nc'

drslib has not been designed to deal with this syntax therefore a work-around is in place to map these files to the following DRS components:

 - activity, product, institute: as configured
 - model, experiment, realm: as above
 - frequency: "fx"
 - mip_table: "fx"
 - variable: "gridspec"
