Repost: Means of indirection in the identification metadata

[<list.mu@c-moria.com>]

[the original was HTML formatted and the examples came out really bad, so
here we go again, plain text]

Dear list members,

I am searching for some advice for using indirection in identification
metadata

I generally like the approach as taken for FRBRauthor 
The semantics of the author role has an indirection allowing me to be very
precise

<FRBRauthor href="#me" as="#author"/>
and
<TLCRole eId="author"
href= "https://my.ontology.com/vocabulary/author#author"; showAs="Author"/>

I would love the same indirection (allowing me to be very precise) on other
metadata too

1. Languages
I have my own language scheme since I need to express documents in Old Dutch
for instance
I have some languages that sit outside the scope of ISO 639-2 alpha-3

I saw that the EU proposes a technique for doing so as expressed in AKN4EU
modelling guidelines

<FRBRlanguage language="od"/>

<TLCReference name="language"
href="https://my.ontology.com/vocabulary/language#old_dutch"; showAs="od"/>

mandating the @showAs to have the same value as the @language attribute in
the FRBRlanguage and mandating the @name to be 'language'

That would work for me. Though I wonder if that is a common practice
and I also wonder how that would work with @fromLanguage in a
FRBRtranslation

Looking for guidance here, either confirmation that AKN4EU is using a best
practice, or proposing some alternatives
(I must admit I am not too thrilled about the explicit mandate of using ISO
639-2 alpha-3)

2. Format
Same (sort of) applies to FRBRformat
I see everybody seems to use
<FRBRformat value="xml"/>
which makes kind of sense.
However, I want to be more precise (I do have multiple XML variant
manifestations)
Again, some indirection would help

<FRBRformat value="xml"/>
and
<TLCReference name="format"
href="https://my.ontology.com/vocabulary/user-format/xml"; showAs="xml"/>
Is that a common way to do so? Are there better alternatives?

3. Dates
<FRBRdate date="1967-05-08" name="onto:birthday"/>

I want to indicate to the user what the semantics are for onto:birthday
I could do so by adding an XML namespace binding ?onto? to the ontology
namespace
So implicitly I am clear enough about how the onto:birthday should be
understood
(assuming the user that wants to know, expands the value of @name into a
full qualified name and check the expanded uri to the ontology,
I would have https://my.ontology.com/vocabulary/date/birthday dereferenced
for information

xmlns:onto="https://my.ontology.com/vocabulary/date/";
<FRBRdate date="1967-05-08" name="onto:birthday"/>

In case I want to be more precise and not assume the xml namespace binding
would be used for uri expansion?

<TLCReference name="date"
href="https://my.ontology.com/vocabulary/date/birthday";
showAs="onto:birthday"/>

Would that then be an acceptable way of expressing that semantics better?

Very happy to hear your views,
Thanks in advance

Geert Bormans, C-Moria