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Reagle's comments on XML Schema

From: Joseph M. Reagle Jr. <reagle@w3.org>
Date: Wed, 10 May 2000 12:48:14 -0400
Message-Id: <>
To: www-xml-schema-comments@w3.org
Cc: "IETF/W3C XML-DSig WG" <w3c-ietf-xmldsig@w3.org>

The following comments are (mainly) editorial comments by Joseph Reagle on
the XML Schema last call Working Draft [1]. 

[1] http://www.w3.org/TR/2000/WD-xmlschema-0-20000407/

Glossary; and Model Groups, Model Group Definitions, and Element
     I find the distinction between these things confusing, perhaps it could
     simplified or more text could be spent on describing how these things
     different. Actually, I look forward to the glossary being completed as
     will help me in understanding the specification. See [2] for more:
2.2 XML Schema Abstract Data Model 
     I could understand this chapter better if the 12 components listed
     somehow corresponded more closely to the 2.2.* section headings.
     Perhaps, a quick definition on each of the 12 components, or a move
     away from the "primary" and "secondary" and "helper" designations
     (towards others) if those terms aren't substantively used elsewhere. 
2.5 Names and Symbol Spaces      
     The fact that you are using the same namespace
     "http://www.w3.org/1999/XMLSchema" across different specifications
     with substantively different syntaxes may cause problems for
     that expect the definition of a dated name space to be stable. See [3]
     more discussion on this topic:
Namespace Prefixes 
     When trying to understand the specifications, I frequently found myself
     bouncing between the primer, structures, and datatypes documents,
     frequently using find or grep facilities to find bits of examples.
Using a
     consistent namespace prefix (xs: or xsd:) through all documents would
     be helpful. 
2.6 Schema-Related Markup in Documents Being Schema-Validated 
     Could the Schema Instance namespace somehow relate to the Schema
     namespace? For instance, I'd find it easier to understand who defined
     the schema instance namespace with something like:
Appendix A (normative) Schema for Schemas 
     It would be useful for XML declarations to include more explicit
     declarations of DTD and schema locations. For instance: 
     <xml version='1.0'?>
     <!-- XML Schema schema for XML Schemas: Part 1: Structures -->
     <!DOCTYPE schema PUBLIC "-//W3C//DTD XMLSCHEMA 19991216//EN" 

     <schema xmlns="http://www.w3.org/1999/XMLSchema" 
      blockDefault="#all" elementFormDefault="qualified" 
      version="Id: XMLSchema.xsd,v 1.1 2000/04/06 13:51:05 aqw Exp"
      xsi:schemaLocation ="http://www.w3.org/1999/XMLSchema.xsd" >

     The more explicit representation of default values in schema component
     definitions is useful. However, the many varied defaults can still be
     confusing, perhaps this could be simplified, or a table could be
     that includes all default values. 
3. Advanced Concepts I: Namespaces, Schemas & Qualification 
     This topic (not necessarily the exposition) is difficult to comprehend
     respect to both comprehending the concepts and as a potential source of
     validation errors in instances I create. Perhaps some guidelines such
     "If you want to create an instance that has no prefixes in children
     elements then X; if you want to create an instance ... Y" so readers can
     easily jump-start their own schema writing. 

Joseph Reagle Jr.   
W3C Policy Analyst                mailto:reagle@w3.org
IETF/W3C XML-Signature Co-Chair   http://www.w3.org/People/Reagle/
Received on Wednesday, 10 May 2000 12:49:19 UTC

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