[dfdl-wg] Plumbing document

[Robert E. McGrath]

| From martinwesthead at yahoo.co.uk Mon Sep  5 11:15:40 2005
| Date: Mon, 05 Sep 2005 14:12:33 +0100
| From: Martin Westhead <martinwesthead at yahoo.co.uk>
| To: Robert E. McGrath <mcgrath at ncsa.uiuc.edu>
| Cc: dfdl-wg at gridforum.org
| Subject: Re: [dfdl-wg] Plumbing document
| 
| Hi Robert,
| 
| See inline:
| 
| Robert E. McGrath wrote:
| > IMO, there is no reason to worry about a detailed definition of streams.
| > 
| > It seems to me that we are simply dealing with sequences of bits, which
| > can be streams or not.
| > 
| > So I see the universe of DFDL as:
| > 
| >    sequence of bits ==> computer science data type ==> seq. of bits
| > 
| > where CS data type is "byte", "int32", etc. (Z, G, et al. in the semantics
| > note)
| 
| There are two issues/points I have with your statement above:
| 
|   1. We have chosen (at this point) the XML/XML Schema data model as our 
| data model. Another way of thinking about what we are doing here as 
| follows: XML Schema provides a way of describing the syntax and type 
| level semantics of XML documents. DFDL extends that capability so that 
| XML Schema can describe other (want to say "all") text and binary formats.
|

Sure. But XMLSchema needs significant extensions to accomplish this.

|   2. DFDL is describing:
| 
|   bits ==> XML type ==> ... ==> XML type ==> ... ==> XML type ==> bits
| 
| i.e. there are arbitrary layers of description that we would like that 
| need to be separable (modular). e.g.
| 
| bits ==> strings ==> ints ==> (back again).

I guess I need to know that the term "XML type" means.  I used the
term "CS data type", meaning something like "32 bit 2's complement integer".

As far as I know, XMLschema provides a markup for some of these, but
I was trying to emphasize the underlying entity.

In any case, IMO, the chain above is actually:

    bits(string encoded) => bits(integer encoded)

Perhaps you have something else in mind for the

     ' strings => ints '

phrase.  If so, I don't understand.

|

---
Robert E. McGrath
National Center for Supercomputing Applications
University of Illinois, Urbana-Champaign
Champaign, Illinois 61820
(217)-333-6549

mcgrath at ncsa.uiuc.edu