RDDL Makes Namespaces More Useful

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RDDL Makes Namespaces More Useful

• Tim Bray, May 2003

2
Road Map

• The problem
• Resource Directory Description Language (RDDL)
• Natures and Purposes
• Where to from here?

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The Problem
The XML Namespaces Recommendation saysThe
attribute's value, a URI reference, is the
namespace name identifying the namespace. The
namespace name, to serve its intended purpose,
should have the characteristics of uniqueness
and persistence. It is not a goal that it
be directly usable for retrieval of a schema
(if any exists).
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Q Should a Namespace URI Point at Anything?

• It doesnt need to for namespaces to do their
  intended job, but
• Names should be first class Web citizens, i.e. be
  grounded in URI space, and
• Why not? Its free!

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Q What Should a Namespace URI Point At?

• A schema (DTD, XSD, RelaxNG, Schematron,
  Examplotron, RDFS)?
• A stylesheet (CSS1, CSS2, CSS3, XSL)?
• Some executable code (Java, .NET, Perl)?
• Human-readable documentation?

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Resource Directory Description Language (RDDL)
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RDDL Credits

• Berners-Lee Raggett proposed a ltresourcegt
  element in 1996
• XML-DEV mailing list over Christmas-2000
  holidays Cowan, Diamond, Dodds, Grosso,
  Jelliffe, Ogbuji, Palmer, Passin, St. Laurent,
  Thompson, van der Vlist
• Jonathan Borden did all the work

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RDDL History

• Original Borden/Bray draft, January 2001, based
  on XLink
• Experiments with RDF forms during 2002
• W3C TAG discussion, 2002-2003
• Minimal RDDL proposal Feb. 2003
• May be blessed in some form by W3C

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RDDL Goals

• Provide a place to go to learn about a namespace
• Should be human-readable for basic bootstrapping
• Should be machine-readable

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Human-Readability

• Use HTML!
• Heres part of a RDDL file

An XML Schema fragment is available which
constrains the syntax of xmllang and xmlspace.
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Machine-Readability

• Based on XHTML
• Two new attributes on the ltagt element linking to
  a related resource
• rddlnature What kind of thing it is
• rddlpurpose What its intended use is

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Example With Source
An XML Schema fragment is available which
constrains the syntax of xmllang and xmlspace.
"
ltpgtAn lta hrefhttp//www.w3.org/TR/xmlschema-0/gtXM
L Schemalt/agt lta rddlnature"http//www.w3.org/
2000/10/XMLSchema" rddlpurpose"http//rddl.org/
purposesschema-validation" href"http//www.w3.o
rg/XML/1998/namespace.xsdgtfragmentlt/agt is
available which constrains the syntax of xmllang
and xmlspace.lt/pgt
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Natures and Purposes
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The Nature of a Related Resource

• Describes what kind of an object it is
• Is a URI reference
• For XML vocabularies, the namespace name (if
  there is one)
• Otherwise based on the media-type
• A predefined list is available at
  http//rddl.org/natures/

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The Purpose of a Related Resource

• Describes intended usage (may be obvious)
• Is a URI reference, e.g. http//rddl.org/purposes
  icon
• A predefined list is available at
  http//rddl.org/purposes(validation,
  schema-validation, module, schema-module,
  entities, notations, software-module,
  software-package, software-project, JAR,
  reference, normative-reference,
  non-normative-reference, prior-version,
  definition, icon, alternate, directory)

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Where To From Here?
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If Youre Building an XML Language

• Give it a namespace name which is a URL, not a
  URN
• Make a human-readable description of what youre
  up to, in XHTML, available at the namespace name
• Add related resources later as you create them

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What RDDL Means

• There are many different flavors of semantics
• RDDL lets you find out automatically which
  semantics have been provided
• This is key for both Web Services and the
  Semantic Web!

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References

• W3C TAG Issue on Namespace Documents
  http//www.w3.org/2001/tag/ilistnamespaceDocument
  -8
• Theses on Namespaces http//www.textuality.com/ta
  g/Issue8.html
• Latest RDDL proposal http//www.textuality.com/xm
  l/rddl3.html

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RDDL Makes Namespaces More Useful

• Tim Bray, May 2003