[OAI-implementers] on the OAI-PMH data model

[Charles Blair]

> I suppose you also generate the different formats on the fly rather than
> actually store persistent versions, right? 

we precompute the metadata portion of the OAI response for all
metadata formats we support. we generate the rest of the response,
including the datestamp, on the fly from a record in our
database. this record also contains a pointer to the precomputed
portion.

> I assume that, for each item, you only persist record datestamps for
> each format you disseminate, 

yes.

> along with a master record datestamp (like Library of Congress), is
> this correct?

no, but only because we don't disseminate master records via
OAI. however, we know what that datestamp would be, so if it were ever
to change, then ...

> And also that every time you actually change the item/master-record
> -- in the day-to-day operation of your repository -- you also update
> all the datestamps you are maintain.

yes.

> In any case, you're doing this to potentially avoid SPs having to repeat a
> historical harvest of records which have not actually changed but appear to
> have because a mapping of the master record onto another format -- say a
> newly adopted format of no relevance to old SPs -- has. Is this also
> correct? 

if we were to add a new format, the records for the new format would
get a datestamp more recent than that for any of our other formats,
because we'd want the harvesters to pick them up. the records for the
old formats would not receive a new datestamp, because nothing about
them would have changed.

> >From a repository-centric perspective, this seems to me quite a service you
> do to SPs and the OAI-PMH. I find it interesting for it shows that, even
> within the OAI-PMH, some service costs may be absorbed by DPs rather than
> SPs. 

you betcha, as we like to say in the midwest. :-)

-- 
Charles Blair           Co-Director, Digital Library Development Center
773-702-8459		University of Chicago Library
chas at uchicago.edu       http://www.lib.uchicago.edu/~chas/