| From martinwesthead@yahoo.co.uk Mon Sep 5 11:15:40 2005 | Date: Mon, 05 Sep 2005 14:12:33 +0100 | From: Martin Westhead <martinwesthead@yahoo.co.uk> | To: Robert E. McGrath <mcgrath@ncsa.uiuc.edu> | Cc: dfdl-wg@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@ncsa.uiuc.edu