[OAI-implementers] error reporting

[lfeng]

it seems error reporting specified at this moment are mostly used by the 
harvester, which I doubt will understand what it means "database is down". I 
think layers of abstraction is a good approach to the error reporting. The 
specification does not stop someone from generating their own debugging 
message, which may not return as part of a xml stream at all, it may very well 
be a log of some kind kept internal. As far as the harvester is conerned, 
either a record is avaliable or not avaliable or when it will be avaliable. 
There may be additional error codes needed, but I think any none OAI protocol 
related errors should be abstracted into layers and handled accordingly.

Louis