I would like to hear other's opinions on the following topic: The distinction between datasets and collections is somewhat artificial. Currently, a collection is just a container for datasets, while a dataset is the "atom" that a user can select. The user often makes further selections from within the dataset. The two kinds of selections (within a collection and within a dataset) can seem very similar, however, selections within the collection are fast (because the server does not have to be contacted), but for selections within a dataset, the user can expect more delays because the server is actually being communicated with. Also selection within a dataset is protocol-dependent. Benno's DODS server seamlessly presents dataset subsets as datasets. Generally in other DODS servers, the client must use constraint expressions (CEs) to do this (ie the subset specification is done on the client, not the server). It would be good to allow catalogers to specify dataset subsets as datasets when that is supported by the protocol, for example using DODS CEs. OK, so two specific questions: 1) how desirable is it to allow collections to also be datasets, meaning that they optionally have a URL and can be selected like a dataset, AND they can be expanded into nested collections and datasets? (Note that this would not make an arbitrary collection into a datset, but only ones that had a URL). 2) If we decide to do 1) then should we simple merge the collection and dataset elements? My feeling is that it makes things a bit harder to understand for new users, but is more compact way to implement this.
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