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20050927: Some general question about thredds/opendap

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.

Ethan

Best regards,

Heiko

--
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:    edavis@xxxxxxxx
P.O. Box 3000
Boulder, CO  80307-3000                       http://www.unidata.ucar.edu/
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