review by a second set of consultants (2008) into the recommendations of the first set of consultants (2005), received by the Eamon Ryan - Minsiter for Communications - recently seems now to be recommending adoption of a Post Code System which will allow a unique post code for most properties - i.e the type of system proposed by GPS Ireland in PON Codes.
See here: http://www.irishtimes.com/newspaper/...629653090.html
This is different to the original Government Post Code Proposal which seemed to suggest an area based system like "D04 123" or "GAL 123" which represented an area of about 20 houses in Dublin 4 and up to 5 or 6 square kilometers in country areas and would not have been of any value for vehicle based services including Emergency Services and SatNav users.
Right now, PON Codes which are available at http://www.irishpostcodes.ie
are the only system publicly available, proven and working which can satisfy the recommendations of the latest consultants. The only satisfactory way to give unique Post Codes to each property is to use Coordinates - i.e. grid references presented in a user friendly and memorable format like PON Codes
An Post uses a database system called the GeoDirectory, the coding in which is unsuitable for use as a Post Code as it is sequential not geographic and has too many characters see comments of Noel Dempsey here: http://historical-debates.oireachtas.ie/D/0605/D.0605.200506290172.html
Also the Geodirectory contains locations of centroids of properties which is not always the most useful if you are trying to gain access from a public road.
PON Codes were developed by a company which is invloved in the GPS mapping and surveying industry - see here: http://www.gpsireland.ie/index.php?option=com_content&task=view&id=47&Itemid=79&limit=1&limitstart=1
Hope this gives you sufficient background to answer your question.