1. Remote Data Access Update
Dr. Dennis Heimbigner
Unidata netCDF Workshop
July 26, 2011

2. Goals
Exploit new dispatch architecture to support a number of new remote access protocols and associated data models
DAP 2 – fully supported now
CDM Remote – in testing
netCDF-RPC – under development
DAP4 – planning stage
Others as they gain traction

3. General issues Serialization/De-serialization
Convert data (and meta-data) on the server to some linear form suitable for transmission across the internet
E.g DAP 2 has DDS and DAS for meta-data and uses XDR for raw data
Underlying client-server protocol
All current and planned will use HTTP protocol
=> something like libcurl on client side and a servlet engine (e.g. tomcat) as the server.

4. CDM Remote Protocol developed at Unidata by John Caron
Goal is to transmit complete CDM data and model
CDM is netCDF-4-like model used in Thredds Data Server
C-client converts CDM to netCDF-4 only
Rationale: DAP2 is not powerful enough to transport complete CDM model
(De-)Serialization provided by Google protobuf system.
Underlying transport is HTTP
Status: working, but needs much more testing for edge cases

5. netCDF-RPC Protocol developed at Unidata by Dennis Heimbigner
Rationales:
Provide a very light-weight client for use on limited devices (e.g. field sensors, cell-phones, etc.)
Allow netCDF-Java read/write access to HDF-5 via netCDF-4 (also keep up with changes in HDF-5)
(De-)Serialization provided by Google protobuf system.
Underlying transport is HTTP (for initial tests)
Status: under active development

6. DAP4 Proposed new version of OPeNDAP DAP2 protocol
Essentially equivalent to netCDF-4 model
Add new atomic types
Add groups and shared dimensions
Use sequences in place of vlen
Use modified version of DAP2 serialization
Use HTTP as underlying transport protocol
Status: planning state => on hold

7. Questions?