Hi Steve,
Yes, I would extend this model also to other relationships about objects or
datastreams. For me, as an outsider (the developers of Fedora might see this
differently), a fedora object is about 2 things: relationships and datastreams.
Internally I know that Fedora stores these relationships in datastreams as well
(and other stores); but as mainly an Fedora API user this is not important to
me. If Fedora decides to combine DC and RELS-EXT or spin-off more datastreams
for different types of relationships for whatever reasons, I would regard this
as a purely internal data-storage matter of Fedora. I would however like to be
able to manage all relationships via a similar API, and where it makes sense a
unified API. I don't see much difference between DC and RELS-EXT in principal,
so I think the same API calls could do both jobs. Datastream relationships are
a bit different as the subject is not a Fedora object I assume, but at least a
similar API would be good. Similar for Fedora Object relationships, which I
assume may differ from DC and RELS-EXT in the fact that they might be read-only
to the user (as they are only generated by Fedora) and you might thus want a
separate API.
If you want to keep the strict distinction, it would be good to at least have a
similar API for DC as you have for RELS-EXT. I know that I can change the DC
datastream as a whole, but this is not without challenges, especially as there
is no locking of datastreams or transaction support outside the Fedora server.
Carsten
Carsten Friedrich
Research Team Leader
CSIRO ICT Centre
M: +61 (0) 2 6216 7019
www.ict.csiro.au<http://www.ict.csiro.au/>
From: Steve Bayliss [mailto:[email protected]]
Sent: Monday, 2 November 2009 21:26
To: Friedrich, Carsten (ICT Centre, Acton);
[email protected]
Subject: RE: [Fedora-commons-developers] Suggestion: Extend Relationship
Management to Dublin Core und bulk relelationship update.
Hi Carsten
I think the distinction is that the API add/get/purgeRelationship methods are
specifically for managing RELS-EXT, not for managing relationships (ie resource
index triples) in general - maybe this should be clearer in the documentation.
Although it would be possible to do what you suggest, there are other
triples/relationships created in the resource index in addition to Dublin Core
triples; for example object and datastream properties, so there is a question
there as to what should happen with these if the relationship API was extended
to a more general case. There's also a question as to what should happen if
the resource index is not enabled - in that case there is no triple expression
of Dublin Core so it might seem illogical for the relationship API to be
modifying DC values.
You're right that DC Terms relationships could be added to RELS-EXT, and these
could conflict with values in the DC datastream, but I think this is a generic
situation - it is possible to have multiple metadata datastreams containing
inconsistent values.
Regards
Steve
-----Original Message-----
From: [email protected] [mailto:[email protected]]
Sent: 30 October 2009 02:31
To: [email protected]
Subject: [Fedora-commons-developers] Suggestion: Extend Relationship Management
to Dublin Core und bulk relelationship update.
The standard relationship management API add/get/purgeRelationship does not
allow to alter or add Dublin Core fields. I'm aware that they are stored
differently internally in Fedora, but from a user point of view, this
distinction is not that obvious. How about changing the current API so the
server side, instead of raising an error on Dublin Core fields, executes the
request on the DC stream (instead of the RELS-EXT stream)?
It would also be nice if the API would accept a collection of relationships as
this could be done with better performance than individual ones (RELS-EXT has
to be changed only once) and the changes on the server side would be small.
In the context of DC there is also the additional problem of DC Terms vs DC
Elements. Just looking at the source code it should be possible to add DC Terms
relationships to a Fedora object using the API which would end up in RELS-EXT
but which might conflict with values in the DC datastream and which would not
be reflected in searches. If you know what's happening inside Fedora it's easy
to avoid, but for someone just wanting to use the API this could be very
confusing.
Carsten Friedrich
Research Team Leader
CSIRO ICT Centre
+61 (0) 2 6216 7019
www.ict.csiro.au<http://www.ict.csiro.au/>
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