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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
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----- Original Message ----- Cc: <thredds@xxxxxxxxxxxxxxxx> Sent: Wednesday, June 05, 2002 1:32 PM > John Caron wrote: > > > One thing I dont understand is what is the relationship between whats > > contained inside the collection vs. whats in the dataset you specify through > > the access element? The user should understand them to be the same (although > > in fact the writer could accidentally or on purpose make them unrelated)? > > It is not a dataset that I specify through the access element -- it is a > DODS access for the collection (collections are the same as datasets -- we > cannot even formulate a reasonable distinction). Most collections would not > have DODS access, but some do. The writer cannot make them different, that > violates the meaning of access belonging to the collection. Sorry, I was using the word dataset rather sloppily to indicate both the THREDDS dataset element, and the "abstract thingy referred to by a DODS URL". To rephrase my question: What is the relationship between whats contained inside the THREDDS collection element vs. what you get back from the abstract thingy? > > > > I > > presume that the ANNUAL, MONTHLY, and SEASONAL datasets are a different way > > of accessing the collection dataset? Or should they be thought of as > > different, but related datasets? > > They are subdatasets, i.e. different ways of accessing the collection > dataset. It sounds like they are different datasets (abstract thingy), in the sense that you would get different data then you would from the original collection data. > In practice this is important because some DODS clients can handle > DODS datasets that contain nest variables (i.e. structures), and some DODS > clients can only handle flat datasets, i.e. a collection of simple variables. > The DODS clients that can handle nesting can use the collection access through > DODS: DODS clients that cannot need to drill farther before using DODS. Its not obvious how a DODS client would know it needs to drill down. There is a valid DODS URL at each level. > > > In this spscific example, you also specify that the collection has a service > > of type Catalog <service serviceType="Catalog" suffix="thredds.xml"/>. What > > is the relationship between that catalog and what is contained in the > > collection? > > a catalog with a single collection is the collection: your formulation as best > I can understand it (i.e. I see no different between catalogs that contain > single collections and collections, which is implicit in your dropping the > level of nesting under that circumstance). I think I should omit that circular > reference (not that the client would get too confused: when it constructed the > url it would find it the url of the document), > e.g. the file should be > > <?xml version="1.0" encoding="UTF-8"?> > <!DOCTYPE catalog SYSTEM > "http://www.unidata.ucar.edu/projects/THREDDS/xml/InvCatalog.0.6a.dtd";> > <catalog> > <service ID="IngridDataset" serviceType="Compound" > base="http://iridl.ldeo.columbia.edu/";> > <service serviceType="DODS" suffix="dods"/> > <service serviceType="Catalog" suffix="thredds.xml"/> > </service> > <service ID="JustDODS" serviceType="DODS" suffix="dods"/> > <dataset name="LEVITUS94"> > <attribute name="fullname" value="LEVITUS94"/> > <access serviceID="JustDODS" urlPATH="SOURCES/.LEVITUS94/"/> > <attribute name="references" value="Conkright:etal1994 Levitus:Boyer1994a > Levitus:etal1994 Levitus:Boyer1994c"/> > > <documentation>LEVITUS94: World Ocean Atlas 1994, an atlas of objectively > analyzed fields of major ocean parameters</documentation> > > <documentation > xlink:href="http://iridl.ldeo.columbia.edu/SOURCES/.LEVITUS94/.dataset_docum entation.html"/> > > <document > xlink:href="http://iridl.ldeo.columbia.edu/SOURCES/.LEVITUS94/.oceanviews.ht ml" > name="oceanviews"/> > <document > xlink:href="http://iridl.ldeo.columbia.edu/SOURCES/.LEVITUS94/.oceanviews2.h tml" > name="oceanviews2"/> > <document > xlink:href="http://iridl.ldeo.columbia.edu/SOURCES/.LEVITUS94/.Zmix.html"; > name="Zmix"/> > <dataset name="ANNUAL"> > <access serviceID="IngridDataset" urlPATH="SOURCES/.LEVITUS94/.ANNUAL/"/> > </dataset> > <dataset name="MONTHLY"> > <access serviceID="IngridDataset" urlPATH="SOURCES/.LEVITUS94/.MONTHLY/"/> > </dataset> > <dataset name="SEASONAL"> > <access serviceID="IngridDataset" urlPATH="SOURCES/.LEVITUS94/.SEASONAL/"/> > </dataset> > </dataset> > </catalog> > > > Benno > > > -- > Dr. M. Benno Blumenthal benno@xxxxxxxxxxxxxxxx > International Research Institute for climate prediction > Lamont-Doherty Earth Observatory of Columbia University > Palisades NY 10964-8000 (845) 680-4450 > > >
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