DAP 4.0 Essential Features

Short List =

1. Version. Encoding/negotiation must use the URL so that client do not need to know about an experimental header (bonus: this will work with protocols other than HTTP).
2. Error. We need a way to reliably report errors when they are detected in midstream of data transmission
3. NGrid.
4. Shared Dimensions

Version

The existing code uses the XDAP HTTP/MIME header. This could be adapted for use with other protocols but that can be cumbersome. This does not work for clients like web browsers without fairly complex setup. Compounding this is that client libraries are not using it.

Another idea: Put something in the query part of the URL. This might look like this:

http://test.opendap.org/opendap/data/nc/fnoc1.nc.ascii?dap(3.2),u[0:1:15][0:1:16][0:1:20]

Although parens are not technically allowed in a URL so the result is often the fairly obtuse:

http://test.opendap.org/opendap/data/nc/fnoc1.nc.ascii?dap%283.2%29,u[0:1:15][0:1:16][0:1:20]

Since this would require changing the CE syntax, we could address the parens issue by adding keywords to the set of allowable things passed in a CE. The resulting URL might look like:

http://test.opendap.org/opendap/data/nc/fnoc1.nc.ascii?dap3.2,u[0:1:15][0:1:16][0:1:20]