This is an old document that captures the starting point of the OPULS design work. It's out of date and should be referenced only as a baseline for the work.
Note that while it's increasingly common for DAP servers to provide different ways that a dataset's metadata may be extended, and often those provide multiple ways of accessing the same underlying data, albeit with different metadata. Those extensions are all accessed by dereferencing a URL and we consider each URL to refer to a unique dataset. This can be confusing because the word 'dataset' is often synonymous with 'file' although there's nothing in DAP2 or DAP4 that makes that association required or calls it out as a case with special treatment