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Re: Reprsenting OGC services in a THREDDS catalog



John Caron wrote:
----- Original Message -----
From: "Daniel Holloway" <address@hidden>
To: <address@hidden>
Sent: Wednesday, June 19, 2002 1:34 PM
Subject: Reprsenting OGC services in a THREDDS catalog

> dimensions.   To make a long story short, all a WMS/WCS
> client really needs is the layer name corresponding to a
> particular collection/dataset to properly access the datafile
> with that service (assuming the client app interacts with the
> server to determine the sample dims, etc.) (Dataset #1
> in the example)
>
>    However, if you want to insure that a particular datafile is
> accessed by the WMS/WCS service, without requiring the
> client to figure out the sample dimensions necessary
> to access that particular datafile, then you would need to
> add the minimal set of sample dimensions necessary to
> uniquely identify the granule in the particular WMS/WCS
> server.  (Dataset #2 in the example)

I would say that this situation is analogous to DODS, in the sense that you
specify a dataset in the catalog, which can be further decomposed from
within the protocol, or as an explicit catalog entry.
 

Actually this might be somewhat different than DODS.  The
primary difference is that you'll never see the actual file
name as part of the URL to a WMS/WCS server.   That request
protocol only provides a layer name and set of sample dimensions
which the server is responsible for translating to specific
data granules, or files for multifile datasets (.i.e., collections).
 
Because urlPath is required on the access element, I hadnt thought of doing
what you do in Example 1:

<dataset name="QS_XWGRD3_2002001.20020041637.Z" serviceName="DODS"
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041637.
Z">
  <access serviceName="FTP"
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041637.
Z"/>
  <access serviceName="WCS" urlPath=""/>
  <access serviceName="WMS" urlPath=""/>
</dataset>

Since you are assuming I think that a blank urlPath means "use the one in
the dataset element". If this was allowed, then the meaning would be:

The dataset is available through WCS and WMS, as

"http://seablade.jpl.nasa.gov/cgi-bin/esip/de.pl/pub/ocean_wind/quikscat/L3/
data/2002/QS_XWGRD3_2002001.20020041637.Z"
 

No, I'm stating that the dataset (.i.e., file) is available through WMS/WCS
and that if the client knows the specific layer name (which I provide in the
property element of the service) that they can access the dataset using the
standard WMS/WCS behavior of query the capability, then request the
map/coverage.   WMS/WCS clients typically operate at the collection
level, not the dataset or granule level though this is not an absolute rule.

The URL you list above is not a valid WMS/WCS request.
The minimum information an OGC WMS/WCS client needs is the layer
name, and path to the service.   The responsibility to identify the specific
datafile from the WMS/WCS server is the client's responsibility, and it's
not obvious that a client could make that distinction without knowing
the mapping of the sample dimensions within the repository.
 

 
though DODS as

"http://dods.jpl.nasa.gov/dods-bin/nph-dods/pub/ocean_wind/quikscat/L3/data/
2002/QS_XWGRD3_2002001.20020041637.Z"

and through FTP as

"http://podaac.jpl.nasa.gov/pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2
002001.20020041637.Z"

(shouldnt protocol type be ftp ?)

Yes, I noticed that mistake as well.
I had thought of doing it this way:

<service name="OGC-DODS" serviceType="Compound" base="">
  <service name="DODS" serviceType="DODS"
base="http://dods.jpl.nasa.gov/dods-bin/nph-dods/"/>
  <service name="WCS" serviceType="WCS"
base=http://seablade.jpl.nasa.gov/cgi-bin/esip/de.pl/>
  <service name="WMS" serviceType="WMS"
base="http://seablade.jpl.nasa.gov/cgi-bin/esip/de.pl"/>
</service>

<dataset name="myName" serviceName="OGC-DODS"
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041637.
Z">
  <access serviceName="FTP"
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041637.
Z"/>
</dataset>

 
or maybe even

<service name="OGC-DODS-FTP" serviceType="Compound" base="">
  <service name="DODS" serviceType="DODS"
base="http://dods.jpl.nasa.gov/dods-bin/nph-dods/"/>
  <service name="FTP" serviceType="FTP" base="http://podaac.jpl.nasa.gov/"/>
  <service name="WCS" serviceType="WCS"
base=http://seablade.jpl.nasa.gov/cgi-bin/esip/de.pl/>
  <service name="WMS" serviceType="WMS"
base="http://seablade.jpl.nasa.gov/cgi-bin/esip/de.pl"/>
</service>

<dataset name="myName" serviceName="OGC-DODS-FTP"
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041637.
Z" />

I think this works best, though you would have to move the WMS/WCS
out of the Compound service, but DODS and FTP would work well
in there for most of the NASA sites.
 
-------------
For example 2:

<dataset name="myName" serviceName="DODS"
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041638.
Z">
  <access serviceName="FTP"
urlPath="pub/ocean_wind/quikscat/L3/data/2002/QS_XWGRD3_2002001.20020041638.
Z"/>
  <access serviceName="WCS"
urlPath="?SERVICE=WCS&REQUEST=GetCoverage&TIME=2002-01-02&LAYER=QuikScat-Lev
el3"/>
  <access serviceName="WMS"
urlPath="?SERVICE=WMS&REQUEST=GetMap&TIME=2002-01-02&LAYER=QuikScat-Level3"/
>
</dataset>

I assume you mean (for WCS, WMS) use the urlPath from the dataset, and
append, so the URL is

"http://seablade.jpl.nasa.gov/cgi-bin/esip/de.pl/pub/ocean_wind/quikscat/L3/
data/2002/QS_XWGRD3_2002001.20020041637.Z?SERVICE=WCS&REQUEST=GetCoverage&TI
ME=2002-01-02&LAYER=QuikScat-Level3"

??

No  you don't use the urlPath from the dataset at all for WMS/WCS access.
Actually my urlPath string (in the access element) shouldn't have included
the 'SERVICE=WCS' or  'REQUEST=GetCoverage', really all that should
be there is the minimal set of sample dimension info, and the layer name.
Those are the elements which are required to uniquely access that specific
datafile from the WMS/WCS server.   Alone they're not sufficient to make
a valid WMS/WCS request, and the assumption is that the client would
add the rest.   However, that would not include the datafile name as in your
example.

The sample dimension and layer name is equivalent to the filename in
the WMS/WCS domain.

Layer=QuikScat-Level3,Time=2002-01-02 ==> pub/.../QS_XWGRD3...637.Z

This discussion might lead us to how you envision an OGC
client using a THREDDS catalog.   It might be possible for a WMS/WCS
client to be developed which will access THREDDS catalogs but I
don't see that happening immediately.   The real benefit from that
community would be for the OGC Catalogs to be able to discover
WMS/WCS layers advertised by THREDDS catalogs.  Actually
I'm not sure of the state of development of the catalog effort in
OGC Map services, we should get some input from the OGC client
developers on how useful the information in THREDDS is to
that community.

Dan
 
 


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