I've been looking at our digital library Application Profile (AP) recently and I'm thinking we will need more than one AP as each product seems to need slightly different local "extensions" to DC. This made me wonder how to manage a hierarchy of APs - where an AP re-uses not just elements from a namespace but (1 or more) entire APs. I've looked through the common AP articles and papers online  but couldn't find any discussion around this, anyone know of any discussions or had any experience?...
I am thinking of the situation where you have say DC-Gov as an AP appropriate for your area, so you want to comply with this (for interoperability) but you also need to add further "optimisations" to make your application work for your users. Perhaps AGLS/NZGLS may fall into this camp (extending DC-Gov, when it is finished)? - in fact any implementation-specific APs based on AGLS/NZGLS would then add yet another layer!
In my situation I am thinking of making a generic "Digital Library" AP but then making additional specific "sub-APs" for each application/product (as each product may follow my common Digital Library AP but (for example) require a one-off element refinement or use a different set of encoding schemes for the same element in the AP, eg. one using only an education vocabulary and another using only a government vocabulary).
I'm guessing it's a case of cut-and-paste-ing the "generic" source AP declaration parts to each sub-AP and then adding the extras around the edges to each? Unless there's a more elegant solution?
On a related note, the SCHEMAS Project website has a draft RDF Schema for defining APs  but the site also mentioned RDFS has limitations for defining APs. Can anyone fill me in on the latest thinking for declaring APs in a machine-readable way?
National Library of New Zealand
 Thomas Baker, Makx Dekkers, Rachel Heery, Manjula Patel and Gauri Salokhe "What Terms Does Your Metadata Use? Application Profiles as Machine-Understandable Narratives" Journal of Digital Information 2 (2), November 2001.
 Rachel Heery and Manjula Patel "Application Profiles: Mixing and Matching Metadata Schemas" Ariadne, Issue 25, September 2000. http://www.ariadne.ac.uk/issue25/app-profiles/
 Makx Dekkers "Application Profiles, or how to Mix and Match Metadata Schemas" Cultivate Interactive, Issue 3, January 2001. http://www.cultivate-int.org/issue3/schemas/
 Fourth SCHEMAS workshop programme http://www.schemas-forum.org/workshops/ws4/programme.html
 Draft SCHEMAS Namespace and Application Profile RDF Schema http://www.schemas-forum.org/registry/schemas/SCHEMAS/1.0/