[OAI-implementers] Sets in OAI-PMH and DSpace

Hickey,Thom hickey@oclc.org
Tue, 21 Oct 2003 13:51:42 -0400

The set structure in OAI is very simple, but also has almost complete
flexibility, so I'm sure you could encode any relationships that DSpace is
aware of in them.  But the retrieval on sets is quite limited, so it isn't
clear what good it would do.  

I agree with Hussein -- keep them simple.  For DSpace, possibly a unique ID
for each collection.


> -----Original Message-----
> From: Tansley, Robert [mailto:robert.tansley@hp.com]
> Sent: Tuesday, October 21, 2003 11:57 AM
> To: dspace-tech@lists.sourceforge.net;
> oai-implementers@oaisrv.nsdl.cornell.edu
> Subject: [OAI-implementers] Sets in OAI-PMH and DSpace
> Hello,
> This is related to a discussion on the OAI-implementers list 
> about moving records in and out of sets.  The next release of 
> DSpace will have some functionality which will affect how 
> DSpace might implement sets.
> Briefly, currently, DSpace has Communities at the top level.  
> Communities contain Collections, and Collections contain 
> Items.  The structure of Communities and Collections are 
> exposed to harvesters via the OAI-PMH set mechanism.  More 
> details are here (see section entitled 'Sets'):
> http://dspace.org/technology/system-docs/application.html#oai
> The forthcoming features that affect use of OAI-PMH sets are:
> 1/ UI tool to add Items to more than one Collection.  This 
> tool may also allow Items to be moved from one Collection to 
> another.  In either case, as highlighted by the 'Moving 
> records in and out of sets' thread on OAI-implementers, it is 
> not clear how the OAI-PMH data provider in DSpace should deal 
> with either event.
> 2/ Allowing a richer Community structure, i.e. Communities 
> can contain other Communities.  This may not be a strict 
> hierarchy; for example, a research project Community may be 
> jointly run by two departments at MIT.  I don't believe this 
> could be expressed in the set structure exposed via OAI-PMH.  
> Additionally, this means the set structure of DSpace at MIT 
> (and other universities) is likely to change significantly 
> and I'm not clear on how this should be exposed via OAI-PMH 
> when the underlying records (Items) have not changed.
> 3/ A Collection may appear in more than one Community.  Again 
> this would seem to break the 'hierarchy' constraint on the 
> OAI set mechanism.
> I can think of a couple of possible directions:
> a/ Drop support for the set mechanism in DSpace completely.  
> It seems a shame to not expose the structure in DSpace, since 
> I can see selective harvesting for a particular Community 
> might be very useful for a department wanting to add a search 
> DSpace function to their Web page/portal/etc.  However, the 
> structure is becoming more complex than the simple hierarchy 
> OAI-PMH allows.
> b/ Expose DSpace Collections as OAI-PMH sets; these would be 
> flat and not a hierarchy.  This would still allow some 
> selective harvesting but harvesters would not be able to 
> harvest by Community which intuitively seems likely to be the 
> most useful selective harvest.  This does still expose us to 
> the 'what happens when an Item is moved between or added to 
> additional Collections' issue however.
> Out of interest, how many people actually use sets for 
> selective harvesting?  My feeling is that while it's not 
> vital now, as the volume of data in systems like DSpace grows 
> it will become increasingly useful.
> Does anyone have any thoughts or suggestions?
>  Robert Tansley / Hewlett-Packard Laboratories / (+1) 617 551 7624 
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