Today I finished some work on the RSS output of GeoNetwork opensource that should allow people to search a metadata catalog for OGC web map services, KML, data for download and whatever else someone decided to publish in ISO19115 formatted metadata.
Providing a search interface with an RSS output allows a user to store his query as a newsfeed and automatically see when there's new content matching his query. Adding the custom links allows some clever clients to exploit the services described in the metadata.
The idea is not new, and we've had a lot of discussions on IRC, email and face to face meetings within the GeoNetwork and OSGeo communities. What I implemented in the end is a common output format in the form of an RSS feed with links that point to the W*S content type and a URL to the service. The service URL should provide enough info for clients to parse it and decide what approach to take: just continue using GetMap, or take the base URL and do a GetCapabilities request first.
Here's a sample: http://geonetwork3.fao.org/geonetwork/srv/en/rss.search?
georss=simple&any=forest&dynamic=on
GeoNetwork offers many search parameters, and I only used the free text 'any' field here, plus a 'dynamic=on' to filter out resources that have a WMS service. The GeoRSS output format is defined by the 'georss' parameter and can be 'simple', 'simplepoint' or 'gml' (default).
The search is also accessible through the OpenSearch interface, producing the same RSS output (connect to http://geonetwork3.fao.org/geonetwork for an example).
A WMS service is represented as a link with the 'href' attribute containing a full GetMap request. The URL might contain variables that are encoded in the same way OpenSearch offers variables. See URI Templates for more details on that.
Here's a sample link:
<link title="Occurrence of forest" rel="alternate"type="application/vnd.ogc.wms_xml"href="http://geonetwork3.fao.org/ows/14066?SERVICE=wms$amp;VERSION=1.1.1&
REQUEST=GetMap&BBOX={geo:box=-180,-90,180,90}&LAYERS={ogc:layer=occurrence_forest}
&SRS=EPSG:4326&WIDTH=200&HEIGHT=100&FORMAT=image/png
&TRANSPARENT=TRUE&STYLES=default" />
I started a small WIKI page here to discuss this further. Don't hesitate to provide suggestions and comments!
