> On Mon, 6 Feb 2006, Zhiwu Xie wrote:
>> This is an implementation question.
>> In schema v1.1 there's an attribute "type" for the "object" element.
>> Although optional, it's set to enumerate either "file",
>> "representation", or "bitstream". I think this attribute is redundant
>> because the objectCatgory contains the same information.

Well, yes and no.  Yes, in that they're intended to convey the same  
of information, but no, in that objectCategory doesn't insist on the  
vocabulary established in the PREMIS model, so in practice, someone
could put any type of information they wanted in there.  My memory of
the discussions was that the flexibility in objectCategory was  
intentional, as
people were a bit reluctant to state that everyone in the world had to
conform to the PREMIS' group's notion of object categories.  So,  
was left as an open string, in case someone decided they needed  
in local practice.  The type attribute is obviously more constrained,  
and was
included so that there could be a dependable, controlled vocabulary for
use between institutions for identifying the category of object.

>> Also it hinders further extension, because in case of more object
>> categories are needed, this attribute needs to be modified each  
>> time an
>> extension is proposed.

That is true, and that is the downside of controlled vocabularies.   
They do
require maintenance.  The upside is having a reliable shared vocabulary
between institutions/applications.  So, there's a cost/benefit  
calculation in
deciding whether to adopt them.  Part of the calculation is the  
of rapid change.  To date, I don't think I've heard anyone say that they
need the set of object categories altered or extended, so I don't  
think it's
imposing a particularly great burden to date, particularly given that  
type attribute's use is optional.

>> Even no extension is expected, it still adds unwanted complexity to a
>> hierarchical schema.
>> I'm working on a schema that first defines an
>> abstract objectType, then extend it to three or even more different
>> types, e.g., fileObjectType, bitstreamObjectType,
>> representationObjectType. If we must have this attribute, I'll  
>> have to
>> further restrict the extended types to accommodate this redundant
>> attribute.

I'm afraid I'm not sure I see your problem.  If you're developing
your own local application profile schema to support PREMIS,
your only real concern is to support the *mandatory* aspects
of the PREMIS schema, and the type attribute isn't mandatory.
So, what exactly is preventing you from creating an abstract
objectType schema which omits the "type" attribute and extends
it from there?

Jerome McDonough, Asst. Professor
Graduate School of Library & Information Science
University of Illinois, Urbana-Champaign
501 E. Daniel Street, Room 202
Champaign, IL 61820
(217) 244-5916
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