[Om3] CDSignatures/@cd, CDSignatures/@type: how to resolve?

[Christoph LANGE]

Dear James,

On Tuesday 13 May 2008 07:49:18 James Davenport wrote:
> On Mon, May 12, 2008 11:41 pm, Christoph LANGE wrote:
> > On Friday 09 May 2008 13:28:29 Christoph LANGE wrote:
> >> Does it always
> >> make sense to assume the same CDBase both for resolving
> >> CDSignatures/@type
> >> and CDSignatures/@cd? For my own needs this questions is a hypothetical
> >> one, but still, could there be a case where the type system CD is in a
> >> different place?
>
> I'm really not up to speed on this. If, as I thought, the argument of
> CDSignature is an MOBJ, then it could specify its own cdbase. I think it
> IS reasonable to specify that, whatever the type system is, the type
> should BE an OMOBJ.

Indeed, that makes sense. So we'd actually require every Signature element in
a CDSignatures to point to a type system CD, e.g.

<Signature name="symbolname">
  <OMOBJ cdbase="cdbase-of-type-system">
    ...
    <OMS cd="type-system" name="type"/>
    ...
  </OMOBJ>
</Signature>

Then it would not even be necessary to have a redundant reference to the type
system CD in the root CDSignatures element – if every Signature contains an
OMOBJ using types from a CD as (cdbase-of-type-system, type-system), then we
know what type system is used. However, I could imagine that the reason for
having /CDSignatures/@type is to enforce that all /CDSignature/Signature
in that signature dictionary use the same type system, and to make processing
easier: If some validator wants to know in what type system a signature
dictionary is written, it would not have to look deeply into the
Signature/OMOBJs.

Still that means that two issues remain:

* if we have redundant information (i.e. the whole signature dictionary and
  the individual type signatures referring to a type system CD) we must 
  ensure (e.g. by explicitly specifying it) that both refer to the same type
  system CD
* if we only refer to the type system CD via a CD name in /CDSignatures/@type,
  we cannot refer to type systems that are located at a CDBase different from
  the one where the CD whose symbols are typed is located (which was my
  original question).

Best,

Christoph

-- 
Christoph Lange, DERI Galway/Jacobs Univ. Bremen, http://kwarc.info/clange

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