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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
John Caron wrote:
A proposed new version of the THREDDS Dataset Inventory Catalog is ready for your comments. Please send them to thredds@xxxxxxxxxxxxxxxx, or to me.I am glad to see some expansion of the spec so that we can convey more information about our datasets. I have a question, however, about switching from DTD to XML Schema.
My view of THREDDS DIC in general is that it allows a data provider to describe their collection of data sets at a level of utility not generally available. I understand there is a considerable effort to generate catalogs automatically for existing collections, and that is important, but I think one can provide information in the THREDDS format that cannot be simply expressed by, for example, a collection of typed files in a directory. So if providers have the detailed information about their datasets, it is probably a set of links on an HTML page (extended documentation in HTML or PDF files, perhaps links to metadata files, etc), along with documentation for the collection as a whole. Also, many providers only provide a few datasets. So the path of least resistance for many is to simply write the THREDDS file.
In light of this, I have been encouraging groups to write THREDDS xml files (version 0.6) to describe their collections. Not that I have had a tremendous amount of success so far, but given some more time, I am hopeful of more to show. For example, there is
http://www.ecco-group.org/thredds/sioeccoCatalog.xml which is displayed in my (Ingrid) interface at http://iridl.ldeo.columbia.edu/%28http://www.ecco-group.org/thredds/sioeccoCatalog.xml%29readthredds/ or http://iridl.ldeo.columbia.edu/SOURCES/.SIO/.ECCO/So given the THREDDS catalog generation options, they chose to write it by hand, and I taught them the nuances of the tags. Pretty reasonable given the small number of datasets and the additional documentation that we wanted to link in. I am a little embarassed that the next THREDDS version is so different from the first, though I guess that is my problem more that anyone elses.
So1) What are the benefits of changing from DTD to XML Schema? Does it include an automatic editing interface easily accessible to everyone? 2) Can you provide a conversion utility on the web so that anyone that has written an old-format file can instantly get a new-format version?
If the new format is much easy to edit than the old (because interfaces are readily available), I think the sell for switching can be made. Otherwise, users may be annoyed, i.e. slow to switch and/or adopt.
-- Dr. M. Benno Blumenthal benno@xxxxxxxxxxxxxxxx International Research Institute for climate prediction The Earth Institute at Columbia University Lamont Campus, Palisades NY 10964-8000 (845) 680-4450
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