DDX

The DDX is an attempt to combine the information in the both the DDS and DAS into one response to eliminate the need to cross-walk the two responses when applying DAS information to variables. It will also streamline access somewhat and will employ XML as the content-type, although these are secondary objectives.

DAP 3.1

DAP 3.1 contains an implementation of this feature, which is described, in spirit, in the original Draft DAP 4 specification document.

DAP 3.2

Implemented

Version information and the structure of the Dataset element

The information in the DDX Dataset element is different starting with DAP 3.2. For this version onward, the Dataset element will contain a default namespace that is http://xml.opendap.org/ns/DAP/3.2# where the last pathname component will vary to reflect the version number. This will also be set as a prefix like dap3.2 so that attributes can be put in the namespace. The Dataset element will also have the schema location set to http://xml.opendap.org/dap/dap/3.2.xsd where, again, the last part of the pathname will reflect the version.

Here's the current stuff that appears in a 3.2 DDX's Dataset element:

<Dataset name="fnoc1.nc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xml.opendap.org/ns/DAP/3.2#  http://xml.opendap.org/dap/dap/3.2.xsd"
xmlns="http://xml.opendap.org/ns/DAP/3.2#"
xmlns:dap3.2="http://xml.opendap.org/ns/DAP/3.2#"
dap3.2:version="3.2">

Suggestions

Adopt the use of MIME that is used by WCS 1.1.

Modify Attributes so that they appear 'anywhere' in the DDX and eliminate the Attribute element. At the same time, every Attribute must be in a namespace to bind that attribute to some semantic context. We will define an 'opendap' namespace for stuff that's not clearly part of CF, FGDC, et cetera.