----- Original Message ----- From: "Joe Wielgosz" <address@hidden> To: "John Caron" <address@hidden> Cc: <address@hidden> Sent: Tuesday, May 14, 2002 3:52 PM Subject: Re: New Catalog XML Draft > John, > > I like it. > > My suggestions: > > 1) Don't restrict service types to known values. It is certain that > people will want to add new service types, so the catalog format should > be extensible in this area. > > In order to prevent ambiguity (does "dods" equal "DODS" equals > "distributed oceanographic data system"?) perhaps these types could > somehow resolve to the url of the service's home page (e.g. > DODS->http://unidata.ucar.edu/packages/dods). I don't know the most > XML-savvy way to do this but perhaps the known mappings can be included > in the DTD? > > 2) Same suggestion for metadata types. In both these cases, the XML thing to do is to use a URI as a unique identifier. The options are eg: 1. xlink:arcrole="http://unidata.ucar.edu/packages/dods" vs 2. metadataType="DODS" Pros of 1: allows services to be added by anyone, URI optionally point to explanation Pros of 2: compact, explicitly documents allowable types > > 3) How about a catalogNS attribute, that can be added to <catalog>, > <collection>, or <dataset>? This would specify a namespace in which > dataset ID's can be considered unique. > > For example, if a THREDDS-crawler found two catalogs with > catalogNS="http://cola.iges.org/thredds", and both contained a dataset > with ID="avn0300", then it could consider these two datasets identical. > > This would make it possible to uniquely identify datasets in multiple > catalogs (in fact across the entire THREDDS web). really good idea, i'd probably use "datasetNamespace" as tag. semantics are that if datasetNamespace exists for a dataset, then datasetNamespace/ID must be globally unique, and the same dataset at multiple locations should have the same datasetNamespace/ID. > > 4) COARDS and CF should go on the list of known metadata types. > > 5) it would probably be clearer if the "DatasetDesc" metadataType was > renamed to "THREDDS". ok, but if we use URI, the list will just be on some web document, rather than listed in the DTD > > 5) IMHO, the dataType attribute is metadata. Thus it should be part of > the THREDDS/DatasetDesc metadata file, rather than the catalog itself. It did occur to me to put it in the DatasetDesc when I made it optional. The use case is if a client can only read GRID files, you'd like to eliminate the non-GRID datasets without having to dereference a whole lot of other XML files. So it could be thought of as a keyword for fast filtering. As for "metadata", I'd say everything in a Catalog is metadata, but i agree its more like DatasetDesc metadata than Catalog metadata. > > 6) How about allowing inline dataset metadata, via a <metadata> tag? > Then it would be possible for a site to completely describe its holdings > in a single file if necessary. that's a good idea, could make it like <documentation> which can be a reference and/or inline. In fact, perhaps <documentation> should becode <metadata> of type "documentation" ?
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