In order to create metadata for both static datasets and dynamic, online services and for use with CSW, the OGC created an xml schema that merges the schema for ISO19115 (dataset metadata) and ISO19119 (service metadata) (see secion D.1.5, page 105 in OGC 07-045). The way that was accomplished was by creating a schema located at http://schemas.opengis.net/csw/2.0.2/profiles/apiso/1.0.0/apiso.xsd. The contents of that schema are quite simple -- it looks like this:

CSW requirements

appears to mostly be compiled by Armin Retterath, Kompetenz- und Geschäftsstelle GDI-RP

Has listing of active CSW servers, some requirements listings

http://www.mapbender.org/CSW_Requirements