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

[Mike Beckerle]

There are two topics mixed together under "pointers" in my mind.

1) data contains a "pointer" or "address" in a given location, and we want 
to abstractly describe things like how big it is. For example, if my file 
format comes from a C language struct containing:

int x;
char* y;

how big is the char* element 'y' anyway? Could be 4 bytes, could be 8 
bytes. 

2) reconstructing the pointer relationships within data. That is, the data 
is conceptually a graph of objects with pointers to each other. We want 
not only to access these pointers within the data but be able to traverse 
them in order to reference other objects within the data.

Now (1) in the absence of (2) is a matter of just expressing how big the 
data we'll be ignoring and skipping over is. This is pretty easy to 
resolve.

(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
unique, key, keyref - that is, what XSD calls "Identity Constraints"

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.

Mike Beckerle
Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA



Mike Beckerle/Worcester/IBM at IBMUS 
Sent by: owner-dfdl-wg at ggf.org
09/02/2005 04:34 PM

To
"Robert E. McGrath" <mcgrath at ncsa.uiuc.edu>
cc
dfdl-wg at gridforum.org, owner-dfdl-wg at ggf.org
Subject
split into multiple topics - Re: [dfdl-wg] Issues: additional data types







I'd like to split this topic into several distinct ones: 

Arrays - I have a placeholder for this in the doc. 

Opaque and "code" types are separate. This is related also to the concept 
of "open content". 

Enums 

Bitfields 

Pointers 


Mike Beckerle
Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA 


"Robert E. McGrath" <mcgrath at ncsa.uiuc.edu> 
Sent by: owner-dfdl-wg at ggf.org 
09/02/2005 03:13 PM 


To
dfdl-wg at gridforum.org 
cc

Subject
[dfdl-wg] Issues: additional data types








Greetings,

Here is an "issue" for the DFDL: additional data types that should
be considered.

Please see attached.

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

mcgrath at ncsa.uiuc.edu 
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