Re: [thredds] service types in THREDDS Catalog

• To: Jeff deLaBeaujardiere <Jeff.deLaBeaujardiere@xxxxxxxx>
• Subject: Re: [thredds] service types in THREDDS Catalog
• From: John Caron <caron@xxxxxxxxxxxxxxxx>
• Date: Thu, 15 Oct 2009 09:44:28 -0600

Jeff deLaBeaujardiere wrote:

John C. & Ben D. (CCing THREDDS mailing list, but it will probably bounce as I'm not a member)-

The THREDDS catalog accepts the following OGC service types:
         <xsd:enumeration value="WMS"/>
         <xsd:enumeration value="WFS"/>
         <xsd:enumeration value="WCS"/>

(ref. http://www.unidata.ucar.edu/projects/THREDDS/tech/catalog/InvCatalogSpec.html#serviceTypes).

I have a couple of questions:

(1) How could we get OGC SOS (Sensor Observation Service) added to that list?

(2) What does the Catalog do when it encounters an OGC service type? Is the granularity of the Catalog only at the service level, or does it actually catalog the data holdings from the service?

Regarding #2, I would think that useful behavior would be to:

(a) issue the GetCapabilities request and get back the list of map layers (WMS), features (WFS), coverages (WCS) or observation offerings (SOS) available from that server. (b) be able to construct request URLs for GetMap (WMS), GetFeature (WFS), GetCoverage (WCS) and GetObservation (SOS) using sensible defaults for some of the parameters. (c) when displaying search results, show a list of URLs like those in #b to allow the user to click through. It is up to the user to be able to interpret the result image, binary or XML data.

These questions are arising because the IOOS (Integrated Ocean Observing System) is in need of a catalog, and it might be that THREDDS would be a possible solution (our service types include DAP+WCS via TDS, WMS and SOS).

Regards,
Jeff DLB

Hi Jeff:

One has to distinguish THREDDS Catalogs from the THREDDS Data Server (TDS) :

A THREDDS Catalog is an XML file,  which can be used by any program or service to 
describe online data resources. We enumerated some of the common service types in the XML 
schema as a semi-controlled vocabulary. "semi" because you can place any 
service type there and the XML will validate against the schema. The service is used to 
construct the URL for a dataset. The service type tells the consumer of the catalog how 
to process the dataset URL, eg what protocol to use.

The TDS implements a subset of those service types (OPeNDAP, WCS, WMS, 
HTTPServer). In those cases, the dataset URL is an endpoint for that service, 
and the client must know how to process it further. The TDS does not implement 
the SOS service.

So the short answer is that if IOOS has an SOS server, it can use a THREDDS catalog to 
describe it. We can add SOS as one of the enumerated types, though you dont have to wait 
for a revised schema to create valid catalogs. Its up to the server to "do the right 
thing" in reponding correctly to the SOS endpoint for a dataset.

If you are interested in adding an SOS service to TDS, well then theres a lot 
more to talk about.


Regards,
John

• Follow-Ups:
  • Re: [thredds] service types in THREDDS Catalog
    • From: Robert Casey

• References:
  • [thredds] service types in THREDDS Catalog
    • From: Jeff deLaBeaujardiere