Re: I can has GetCapabilities media types?

Thanks Maik, I agree this sounds like a CR against the WMS spec ?

ed


On Sun, 31 Jan 2016 at 12:17 Maik Riechert <m.riechert@reading.ac.uk> wrote:

> Dear all,
>
> As you may know, all OGC web services have a root GetCapabilities
> document that contains metadata about the content and functionality of
> the service. When I want to advertise an OGC web service as a whole
> somewhere, then this is the web resource to use.
>
> Example:
>
> http://sampleserver1.arcgisonline.com/ArcGIS/services/Specialty/ESRI_StatesCitiesRivers_USA/MapServer/WMSServer?REQUEST=GetCapabilities
>
> Now, imagine you have a dataset which is published as a zip file but
> also as a WMS service (for having rendered map layers) and a WCS service
> (for programmatic access to the data):
>
> http://example.com/mydataset
> http://example.com/mydataset/324hh42 (zip file)
> http://example.com/mydataset/kkj423kl?REQUEST=GetCapabilities (WMS)
> http://example.com/mydataset/nknklnkl23?REQUEST=GetCapabilities (WCS)
>
> I used random characters on purpose here, could be some database ID.
>
> Since I want my dataset to be easily ingestable in CKAN and other
> catalogs, I decide to describe it in terms of DCAT, meaning I write a
> DCAT description in some RDF dialect and put that file somewhere so that
> I can give it to CKAN admins and tell them to start ingesting my dataset
> metadata.
>
> To make a long story short: There's no way for a machine to easily
> differentiate between different OGC services (here WMS and WCS), or even
> saying it is an OGC service at all, in DCAT distributions. Why not?
> Because all OGC GetCapabilities requests come back as a generic
> text/xml, meaning that no specific media types exist for different OGC
> GetCapabilities service types, which means I can only put "text/xml" as
> media type in my DCAT distribution, and that is pretty meaningless. It
> also means that an automated client first has to load that distribution
> to figure out it is actually an OGC service. And *that* in my opinion is
> not very discoverable or efficient.
>
> ArcGis, MapServer, and possibly others support the
> "application/vnd.ogc.wms_xml" media type for both WMS GetCapabilities
> and GetFeatureInfo. I'm not sure who exactly invented that, but it's not
> OGC I think. I couldn't find an equivalent for WCS.
>
> CKAN itself has a special "format" field with hardcoded constants for
> identifying certain APIs like "wms" etc. But there is no reliable way to
> derive that field from a DCAT distribution at the moment.
>
> Since OGC web services in their current form will not disappear any time
> soon, I strongly suggest to at least fix this minor problem by defining
> media types for the GetCapabilities documents, which is more or less
> equal to a service endpoint.
>
> Some suggestions...
>
> application/vnd.ogc.wms+capabilities+xml
> application/vnd.ogc.wcs+capabilities+xml
> ....
>
> Thanks
> Maik
>
> PS: When I query the RDF/DCAT interface of CKAN, I get back
> dct:format="wms". And I parse that and hope for the best. Enough said!
>
>
> --

*Ed Parsons*
Geospatial Technologist, Google

Google Voice +44 (0)20 7881 4501
www.edparsons.com @edparsons