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@IBMUS Sent by: owner-dfdl-wg@ggf.org
09/02/2005 04:34 PM
To
"Robert E. McGrath"
<mcgrath@ncsa.uiuc.edu>
cc
dfdl-wg@gridforum.org, owner-dfdl-wg@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@ncsa.uiuc.edu>
Sent by: owner-dfdl-wg@ggf.org
09/02/2005 03:13 PM
To
dfdl-wg@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