1. Dispatch Layer and the NetCDF Architecture
Dr. Dennis Heimbigner
Unidata netCDF Workshop
July 26, 2011

2. Overview Goal: netCDF as universal API Dispatch Architecture
Dispatch table selection rules
Questions

3. Goal: netCDF as the universal API
Actual semantics of nc_open or nc_create determined by choice of dispatch table
Currently support: netCDF-3 (classic), netCDF-4, OPeNDAP, and CDM-Remote
Proposed additions: HDF-4 EOS, DAP4, RPC
Allow for user-community defined extensions

4. Dispatch Architecture
Path
Mode flags
Path Prefix
Existing File
Client
Program
nc_open()
nc_get_var() …
nc_close()
netCDF API
Wrapper
Procedures
nc_open()
nc_get_var() …
nc_close
Dispatch
Table
For e.g.
Netcdf-4

5. Dispatch Selection Rules
The dispatch table is chosen in the NC_create and the NC_open wrapper procedures
The decision is based on the following pieces of information.
Path – regular file, url, or something else
Path prefix – e.g. [cdmremote]<url>
Mode argument – a specific flag (e.g. NC_NETCDF4)
Contents of existing file (when using nc_open)
NC_set_dispatch_override()
Environment variables (not currently used)

6. Questions?