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Good points. We are also troubled by the inheritance implications of a WEMI model realized in RDF. In the OCLC linked data model of works, every description is modeled as a schema:CreativeWork and is capable of standing alone. So an Item description could have titles, subjects, authors, and so on, which might be factored out to Works, Expressions, and Manifestations in a hierarchical model. We are still debating among ourselves whether this result is theoretically interesting, or whether it's a concession to the reality of working with aggregated data. But I'm wondering where BF stands on this issue.
From: Bibliographic Framework Transition
Initiative Forum <[log in to unmask]> on behalf of Karen Coyle <[log in to unmask]>
Sent: Tuesday, June 23, 2015 6:01 PM
To: [log in to unmask]
Subject: Re: [BIBFRAME] The BIBFRAME Item Proposal: What we learned by mapping it to Schema.org
On 6/22/15 2:24 PM, Godby,Jean wrote:
Questions and minor issues
- How are the properties partitioned among 'Instance and 'Item'? The example described in the Proposal document implies that the 'Item' class contains only properties indicating uniqueness -- such as shelf location, bar code, etc -- while Instance would contain properties such as 'contributor,' 'creation date,' and 'custodial history.' Is this correct? Or is there any bleeding between the Instance/Item line? For example, can an Item have an author or title, or is that information always maintained in the corresponding Instance description?
Jean and Jeff,
Great, and deep, analysis.
As to the above, I actually see this as more than a minor issue (and I suppose you meant it as a question). This concept of a kind of "daisy chain" of bibliographic levels was introduced in FRBR, but FRBR was conceptually modeling a database design, not RDF. Folks often talk about "inheritance" between, say, works and instances and items, but in fact there is no inheritance in RDF. (There is in object-oriented programming, which may be why people assume that it exists here.) Given that RDF is kind of like disconnected bits of DNA that you hope will all be there where you go looking for them, I see a danger in relying on a graph two or three "links" away for essential information.
I don't see why there cannot be a direct relationship between items and authors. It could be just another set of graph relationships to the same resources, or a shared identifier for the item/instance/work "package". For some materials, e.g. art works or museum pieces, the item will be the main focus of information and the separation into work/instance/item may not be worth the costs.