Question about isbn and other standardized numbering schemes

Hi all,

I'm a researcher examining the plausibility of walking library MARC format
metadata into the schema.org ontology. I see that one of the properties of
schema:Book is schema:isbn. I had two questions.

1) Is there a generic property that allows me to assert additional
identifiers, such as classification numbers (e.g. LCC number)?

2) Is the model's expectation that all books have ISBNs? Because that
simply isn't true. At best ISBN is a contingent property of books (some
have them and some do not, especially as you track back in time). Does this
mean that schema:isbn is an optional property for schema:Book(s)? Doesn't
it make more sense to just have a more generalized property that works with
any standardized numbering scheme?

For example

schema:Book schema-ex:identifier schema-ex:Identifier .

schema-ex:Identifier schema-ex:identifierType schema-ex:IdentifierStandard .

And then have a similar set of properties for standardized classification
schemes.

Thanks,

Jacob

_____________________________________________________
Jacob Jett
Research Assistant
Center for Informatics Research in Science and Scholarship
The Graduate School of Library and Information Science
University of Illinois at Urbana-Champaign
501 E. Daniel Street, MC-493, Champaign, IL 61820-6211 USA
(217) 244-2164
jjett2@illinois.edu