Relevance & expected benefits
GeoDCAT-AP was designed to enable the cross-sector and cross-platform sharing and re-use of INSPIRE and, more in general, metadata following the ISO 19115/19119 standards and the corresponding XML-based implementation (ISO 19139).
To achieve this, GeoDCAT-AP defines transformation rules from INSPIRE / ISO metadata to DCAT-AP, which is currently the de facto standard metadata interchange format across European data catalogues.
These transformation rules can be run on top of the existing INSPIRE infrastructure, without requiring any internal modification, and can be directly used to expose metadata available via a CSW (Catalog Service for the Web) in GeoDCAT-AP.
Evidence
A reference implementation of GeoDCAT-AP is available, that can be used to transform at runtime INSPIRE / ISO 19139 records, and that can be applied also on top of a CSW (Catalog Service for the Web). This reference implementation is used in a number of catalogues, one of them being the European Data Portal.
There are also implementations of GeoDCAT-AP for CKAN.
A document describing (some of) the existing implementations is available at the GeoDCAT Application Profile for data portals in Europe.
A draft for an OGC (Open Geospatial Consortium) Best Practice document is currently under development, and there are discussions to endorse GeoDCAT-AP as an OGC Community Standard.
Limitations
The transformation rules defined in GeoDCAT-AP concern ISO 19115:2003. The level of compatibility with the latest version of ISO 19115 (ISO 19115-1:2014) has not been tested. The GeoDCAT-AP specification includes nonetheless in an appendix a review of the main changes introduced in the latest version of ISO 19115.