[OAI-implementers] handling unavailable data

[Ben Henley]

	Thanks for the help. Should a note about this point perhaps be added
to the protocol?

> -----Original Message-----
> From: Hussein Suleman [mailto:hussein@vt.edu]
> Sent: 29 March 2001 21:42
> To: Ben Henley
> Cc: 'oai-implementers@oaisrv.nsdl.cornell.edu'
> Subject: Re: [OAI-implementers] handling unavailable data
> 
> 
> hi
> 
> i would think returning empty lists is not a good idea because the
> service provider could make long-term assumptions based on 
> that - in the
> case of ListMetadataFormats that there are none.
> 
> my suggestion would be to use HTTP error codes to indicate that the
> server cannot respond because of some internal problem ... 
> for example,
> you could use "503 Service unavailable" and possibly return a
> "retry-after" time, which supports  automatic harvesters quite nicely
> (even the repository explorer will honor those) ... for 
> completeness, if
> you want a really solid interface, you might consider using 
> some flavor
> of upper-bounded exponential backoff so that the retry-after times
> follow a 1,2,4,8,...,r sequence for subsequent requests while the
> database is unavailable.
> 
> hope this helps ...
> 
> ttfn