This is terrific, Richard. I look forward to hearing more. 

Thanks much,
- Bill

On Jan 28, 2009, at 3:59 AM, Richard Green wrote:

Bill (and others)
I like the idea of a BOF at OR09.  Some of you may recall that we floated the idea of a registry of BDefs and BMechs at OR07 but this effort stalled, not least because of the news of the CMA in the coming Fedora 3.
I think I mentioned in a previous mail that the Hydra Project (Hull, Stanford and Virginia with Fedora Commons) is developing some generic materials and these include content models for Ďcommoní objects and the SDef/SDeps to go with them.  We have a number under test at the moment.  Iím pretty certain that we shall share these with the community as soon as we have done some serious testing with them Ė OR09 would probably be just about the right timing.  (Note these are my opinions, I havenít consulted the others specifically.)  Our intention would be that these would then be available from somewhere in the Fedora Commons web sitesí structure.
The Fedora wiki has recently been given a placeholder for the Hydra Project (bottom left of the dashboard).  I will make a commitment to get the space populated with public details of the project and something about its potential outputs to the community in the next fortnight.  Iíd do it sooner but (a) Iím snowed under with work at the moment and (b) several key Hydra people are unavailable this week and Iíd want to check the essence of the proposed text with them first.
Richard Green
Manager, RepoMMan, RIDIR and REMAP Projects
e-Services Integration Group
From: Bill Parod [] 
Sent: 27 January 2009 23:27
To: Gramsbergen, Egbert
Cc: Fedora Commons
Subject: Re: [Fedora-commons-users] Content Model question
These all seem like good reasons to float some 'out of band' agreements on cmodels - towards the registry idea. We could probably get a BOF or other event scheduled (if not already on the agenda) for the OR09 / Fedora Days meeting. We can also share / develop some models and work in that direction in the mean time. Is there a forum or natural place to collect such things on the wiki or elsewhere?
- Bill
On Jan 27, 2009, at 4:38 PM, Gramsbergen, Egbert wrote:


I found out by experiment that if more Service Deployments apply for a
given data object plus Service Definition (this might be because the
data object subscribes to more Content Models but not necisarily so),
you will receive an error message because the system cannot decide which
one to use.
Maybe(?) future versions will have inheritance in Content Models, so the
system would be able to choose the most "specific" SDep in some of these


Egbert F. Gramsbergen
TU Delft (Library) - Digital Product Development    +31(0) 15 27 82922

-----Original Message-----
From: Scott Prater []
Sent: Tue 1/27/2009 4:09 PM
To: Bill Parod; Fedora Commons
Subject: Re: [Fedora-commons-users] Content Model question

 From the horse's mouth...

"A Data object may assert a hasModel relationship to multiple CModel
objects. Such a Data object should conform to all of its Content Models,
containing an aggregation of all the Datastreams defined by the Content
Models. If two or more Content Models define Datastreams which have the
same name but different characteristics, no well-formed Data object can
be constructed and likely the repository will be unable to deliver its
content or services."

I haven't found anything that mentions how Fedora handles digital
objects that belong to Content Models with the same or similar SDefs but
different deployments, however.

-- Scott

Scott Prater wrote:
> Hi, Bill --
> Yes, my sense reading the Fedora docs and wiki is that the CDMA is
> designed primarily to enable Content Model reuse and sharing, by making
> them as modular as possible.  This, I think, is the whole point of the
> mix-in idea, the ability to subscribe a digital object model to as many
> Content Models as is necessary to adequately describe the object and its
> behaviors, but no more.  One of the great things about this mix-in
> approach is that someone else (such as you) could take my objects,
> import them, and add/override more Content Models to them to refine them
> even further.
> One danger we've discussed here, though, is what happens when Content
> Models begin to step on each other.  We haven't tested this out yet, but
> what happens if Content Model A implements foo(), and Content Model B
> also implements foo(), and digital object Bar is a member of both A and
> B?  Which implementation of foo() gets executed?  Or, in the case of
> datastreams, what happens if Content Model A says the object must
> contain a datastream FOO of mime type text/xml, and Content Model B says
> the object must contain a datastream FOO of mime type text/html?  Which
> (if any) constraint is applied to digital object Bar?
> A wide, rich plethora of atomistic Content Models can open yourself up
> to that kind of confusion.  That would be something that would need to
> be taken into account also when designing a shareable Content Model
> registry -- anyone who implements your Content Models will need to know,
> preferably up front, if your Content Models are going to overlap with
> theirs.
> -- Scott
> Bill Parod wrote:
>> This has been a real interesting discussion. It brings up a design
>> principle I've wondered about with CMDA: Does one view cmodels for
>> data integrity or service readiness? That is, if you're using cmodels to
>> enforce object completeness (data integrity), you might be inclined to
>> express rich cmodels that thoroughly describe complex objects. However,
>> if your goal is to maximize your objects' reusability (service
>> readiness), you might be inclined to express multiple cmodels that are
>> simpler with minimum datastream requirements so that a given object is
>> more likely to match requirements for more services.  I've been tending
>> toward the latter approach since CMDA. I think this is in the spirit of
>> what Scott suggested, (is that right, Scott?) but with premium on
>> satisfying likely service opportunities. 
>> Of course, one can go both ways, declaring complex cmodels for
>> integrity, profiling, or more demanding service requirements. And also
>> break those out simply to enable contractual promiscuity. So maybe this
>> is a non-issue.:) But if there's community potential for cmodel and
>> service registries, it might be good to map this out a bit and see where
>> there are natural cmodel/service agreements/opportunities. Are there
>> other trade-offs to consider? How are others approaching this?

Scott Prater
Library, Instructional, and Research Applications (LIRA)
Division of Information Technology (DoIT)
University of Wisconsin - Madison

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