[OAI-implementers] Requesting a part of a record possible wit
Thu, 22 Jan 2004 11:10:29 +0100
Sorry about the late answer.
Thank you very much for all your comments and the summary, your input
helped me very much.
Here is the summary from my perspective:
I understand, that the actual version of OAI-PMH can request a whole
record (XML document), but not a part of record (a fragment of XML
The proposal from Naomi (1) is a workaround, which will work if it's
only necessary to request only a few defined parts of a record.
Jeffs proposal (2a) has the attractive idea to request a part of a
record by the means of XPATH. In my eye's it's a drawback to depend on a
external service for the reason, that the "main" protocol (OAI-PMH) is
lacking this feature (nothing against external services). I would like
to think more about a general solution (for DDI). But nevertheless,
Jeff, thank you very much for your offer.
Hussein's proposal (2b) of a new protocol on top of or parallel to
OAI-PMH sounds very good. The proposed way to add this new protocol
seems to be very flexible also for other new protocols, it would be a
way of a general extensibility of OAI-PMH. The question seems to me: is
"requesting a part of record" not a candidate of a new version of
OAI-PMH? "GetRecordPart" and "ListRecordParts" were the tools I'm
The actual version of OAI-PMH has the intention of requesting whole
records (primary use of harvesting protocol). The question of requesting
a part of a record by the means of XPATH will arise with large XML
documents. The service provider could be interested only in a part of
the information. Large XML documents have usually DTDs/Schemas with a
deeply nested structure and a lot of elements or have repeatable
elements which could be repeated very often.
The size of DDI files reach often 500-1000 KB. The description of a
social survey consists often in several hundred questions/variables and
in an extensive general study description.
I see one problem with the idea to request fragments of a XML document
stored in a record: the client would not be able to validate the
response, because itís only a fragment of a XML document. A better
solution would be to embed the fragment in a frame of a valid XML
document (like a "condensed version" of a XML document). That would be
dependent from the XML DTD/schema (the question would be, which elements
Right now we are just thinking about using OAI-PMH to offer DDI-files.
Perhaps there is another way to offer XML files for service providers,
Hussein mentioned SOAP.
I will try to give the DDI community
(http://www.icpsr.umich.edu/DDI/users/listserv.html) a hint on this