Integrating Data from Multiple XML Schemas with GRDDL and RDF

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Overview

• Challenge: finding common structures accross XML vocabularies
• Existing strategies, problems
• GRDDL approach, examples

Challenge: How to find the license in all these XML documents?

• has a vocabulary of license terms
  • attribution
  • Noncommercial
  • commercial use
  • ... etc.
• Various communities have XML Schemas for data and metadata
  • NewsML
  • XBRL
  • Open Archives Initiative (OAI)

Strategy A: An XML Schema for Creative Commons License Terms

• an XML Schema for CC license terms is easy enough
• Namespaces allow us to find the terms inside NewsML, XBRL

Problem A1: Host Language Schema too constrained

• XHTML 1.x DTD doesn't have space for "foreign" elements
• xsd:any interacts badly with deterministism constraints in XML Schema
  • ref Orchard Jan 2004

Problem A2: Host Language already has license syntax

• e.g. NewsML Rights Metadata
• use both NewsML markup and CC markup?
  • keeping duplicate data in sync is error-prone
• using only CC markup?
  • misleads consumers that expect <newsml:license>

Problem A3: How to refer to things in the host domain?

• How to say that a license applies to the annual report mentioned 12 lines up in this XBRL document?
• How to say that a license applies to the photo referred to in section 4 of this NewsML document?

Problem A4: When is a license term not a license term?

• when it's an example:

    <xsd:schema>
     <xsd:annotation><xsd:documentation>
      Widget Product Catalog Markup
      Copyright (c) 2005 VendorCo all rights reserved
     </xsd:documentation></xsd:annotation>
     ...
     <xsd:element name="digitalProductRights">
      <xsd:annotation><xsd:appinfo > <!-- example -->
        <cc:license><cc:shareAlike/><cc:license>
      </xsd:appinfo></xsd:annotation>
      

• when it's quoted
• when it's in an XSLT stylesheet

Strategy B: Use RDF

Sidebar: RDF in a Nutshell

• Make terms out of URIs
• Make simple statements using URIs from any namespace: <doc1> prism:license cc:ShareALike.
• Statements do not interact; partial understanding is OK
• Encode the statements in XML
  • <rdf:Description rdf:resource="doc1"> <prism:license rdf:resource="&cc;ShareAlike" /> </rdf:Description>
  • sometimes not aesthetic: hold your nose!

Strategy B: Use RDF (cont)

• When all parties accept the constraints, it works well enough
• RDF/XML can be ugly, verbose
• only simple statements standardized; questions, rules, quoting etc. TBD
• RDF not as widely known; lots of XML data doesn't use RDF (yet? ever?)

Strategy C: GRDDL

• Use RDF statement structure, URIs for terms
• Relax syntactic constraints; use XSLT to normalize

GRDDL example 1

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GRDDL Issues

• XSLT literal thing result element... ouch!@@