[Geodata] OpenSearch GEO, OAI-MPH, CSW, GeoRSS. All miss a defined way to transfer service information

[Jeroen Ticheler]

Hi all,
I see a huge number of extremely interesting discussions around  
catalogues happening all at the same time. This is excellent and I  
have good hopes we get to a point where we can bring lots of  
different approaches together! I'm starting a new one here :-)

One observation I have, that I have not seen resolved anywhere (where  
I have looked!?) is how to get information about services across in  
the simple, harmonized Dublin Core format that seems to be the common  
fall back format in all (or most if you wish) the above mentioned  
protocols.

We had an IRC discussion on this today in the OSGeo geodata channel  
(or #telascience on freenode). The issue for me is the following:

ISO19115 can be used to describe a number of online resources (I  
purposely ignore ISO19119 here :-). These resources can be all kind  
of things. W*S, zip files, HTML links, KML, you name it. If I have an  
ISO19115 record, I would like to be able to use these (multiple)  
online resources and show them in my DC formatted output. Without any  
documented agreement, this can not be done AFAIK. we came up with the  
idea to use the (logical) URI field for the links, but add required  
information to that field so that a proper (best guess) assessment  
can be made by the client on what this URI as all about.

Using mimetypes seems like a nice way of doing this. So you would end  
up with a list of URI elements in your DC metadata that could look  
like this:

<URI>mimetype, URI, name, description</URI> (with the 'name' and  
'description' as optional content) (we use name for a wms layername  
in the case of a WMS service for instance)

So:
<URI>application/vnd.ogc.wms, http://geonetwork3.fao.org/ows/1,  
national_boundaries_africa, National administrative boundaries of  
Africa</URI>
<URI>application/vnd.google-earth.kml+xml, http://www.fao.org/ 
geonetwork/srv/en/google.kml?id=2&layers=sub- 
national_boundaries_africa, National administrative boundaries of  
africa, National administrative boundaries of africa</URI>

etc...
This kind of formatting allows most clients to properly asses what  
they can do with the URI provided and is easy to maintain as  
mimetypes are pretty well defined.

OK, maybe nothing new to many of you, but it was an insight we had  
today that I quite liked and that has some potential to work on DC as  
it is now used in most server protocols already without the need to  
modify schemas or so.

We can at that point also start using mimetypes as the content of the  
"protocol" field in the online resources in ISO19115 metadata. This  
is a relief for us compared to our current hacked approach :-)

Looking forward to suggestions on this. Keep up the good discussions!
Ciao,
Jeroen