Pointers - was: Re: split into multiple topics - Re: [dfdl-wg] Issues: additional data types

[Robert E. McGrath]

On Tue, 6 Sep 2005, Mike Beckerle wrote:
> (2) is trickier. I suggest a proposal for pointers in DFDL should begin
> with an analysis of the approaches to pointers in XML and XSD, in
> particular
>

> ID, IDREF - in basic XML
These are only used in attributes, they point to named entities.

> unique, key, keyref - that is, what XSD calls "Identity Constraints"
These operate on Xpaths.

> I'd like to see annotations to unique, key, and keyref allowing these
> logical XSD concepts to be mapped into addresses and pointers within the
> data.
>

So how would this work?

I'm thinking of something like a list (index).

A C data structure is something like:

   struct thing {
      struct thing * next;
      struct blob payload;
   }

In the file, there are a bunch  (not necessarily contiguous!) records,
with a pointer to the next one and a blob.

   next  ->  next -> NULL
   blob1     blob2

How would you want to describe this data?