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Re: 20050927: Some general question about thredds/opendap


I have a question - Will the aggregation server expand at some point to include ADDE or OpenADDE?

Thank you so much!


On Sep 27, 2005, at 1:22 PM, Ethan Davis wrote:

Hi Heiko,

Heiko Klein wrote:

I'm evaluating the usage of thredds for an EU project http:// www.ecmwf.int/research/EU_projects/GEMS/

I installed the 2.0 version and was able to browse some pages and see some data, but I still have some more general questions:

What are the main advantages of thredds against opendap?

THREDDS is not a replacement for OPeNDAP. THREDDS adds cataloging capabilities on top of various data access systems. The aggregation server (and the upcoming 3.1 THREDDS server) provide both OPeNDAP and THREDDS services.

I see a lot of XML files and the last s in thredds is for services: What is the relation between thredds and web-services (http://www.w3.org/2002/ws/) or REST (http://www.xfront.com/REST- Web-Services.html).

Well, THREDDS catalogs are XML documents available over HTTP. Catalogs can reference other catalogs and can also provide links for accessing datasets. Besides catalogs, there are a number of other THREDDS services available. For instance, the Dataset Query Capabilities (DQC) allows users to request a subset of a dataset collection. Current THREDDS services don't use any of the WS frameworks, so I'd say THREDDS is built on "web services" but not "Web Services".

Does thredds include a opendap server (didn't manage to get that working), or is thredds just able to distribute data via an external opendap server. If yes: Is the thredds opendap server able to serve as much data as the generic opendap servers, i.e. grib,hdf4,hdf5?

The current 2.0 THREDDS server includes the aggregation server which can serve netCDF files (and OPeNDAP dataset) individually or aggregated. The upcoming 3.1 THREDDS Data Server can serve all the data that the netCDF-java library can read (nc, GRIB-1 and -2, most HDF5, NEXRAD level II and III, and a few others; see the netCDF- java page for more details ,http://www.unidata.ucar.edu/software/ netcdf-java/).

What is the status of thredds (3.0?), the aggregation server and the query language to search the aggr. server?

The THREDDS Data Server (TDS) 3.1 will be released shortly. The aggregation server is being refactored and will be folded into the TDS at some future date. I'm not sure what you mean by "query langague to search the agg server". The DQC (which I mentioned above) is the only query language we are working on and it is not widely used at this point. But it isn't specific to the agg server.

Hope this clears things up. Let me know if you have other questions.


Best regards,


Dr. Heiko Klein                              Tel. + 47 22 96 33 44
Air pollution Section/Research Department    Fax. + 47 22 69 63 55
Norwegian Meteorological Institute           http://www.met.no
P.O. Box 43 Blindern  0313 Oslo NORWAY       http://www.emep.int

Ethan R. Davis Telephone: (303) 497-8155
Software Engineer Fax: (303) 497-8690
UCAR Unidata Program Center E-mail: address@hidden
P.O. Box 3000
Boulder, CO 80307-3000 http:// www.unidata.ucar.edu/
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