[OAI-implementers] on the extensibility of OAI-PMH

herbert van de sompel herbertv at lanl.gov
Fri May 6 13:28:43 EDT 2005

Fabio Simeoni wrote:
> Hi,
> a 3rd party would like to consider extensions of the oai:recordType
> component of the protocol's schema in order to disclose per-record
> information other than and in addition to descriptive metadata (say
> contained in a <foo> element following the <metadata> element). The extra
> information is optional, in that standard OAI requests simply do not trigger
> its generation; accordingly, the party would very much like this kind of
> extension to be backword-compatible, so that a single implementation of the
> extended server would equally serve old and new clients of the protocol.
> Conceptually such an extension *is* backword-compatible but the protocol's
> schema does not cater for it (why?). The 3rd party must either extend within
> the OAI namespace, which it does not own (apparently a bad practice even
> when technically harmless) or else extend into a new namespace and accept to
> break all namespace-aware old clients. Is this correct and, in case, is
> there a way around it? Or must the 3rd party admit that standard and
> extended implementations of the protol must live (and be maintained) side by
> side at two different URLs? 


I am not sure I understand your question correctly, but assuming I do, here are 
the ways to achieve what I think you want to achieve without having to extend 
the protocol:

(*) Introduce an extra harvestable metadata format - <bar> - that encapsulates 
the "normal" one and the "additional" one (note that using XML Schema, the 
nature of the additional one can be defined in an open-ended manner : any 
namespace ...)


(*) If the "additional" stuff is metadata about the "normal" stuff then put it 
in an "about" container


Herbert Van de Sompel
Digital Library Research & Prototyping
Los Alamos National Laboratory, Research Library
tel. +1 505 667 1267

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