1. RelaxNG Compact Syntax for XDI
Bill Barnhill
XDI TC Meeting
2005 June 29

2. Overview RelaxNG: A short introduction The RNC schema proposal
The RNC schema for XDI
Benefits
The top reason for the XDI TC to adopt RNC

3. RelaxNG: A Short Introduction
Based on TREX, XDUCE, RELAX
Created by OASIS RelaxNG TC
Primary goals...
To be easier to read and construct
Efficient parsing via a solid theoretical basis
Supports XML namespaces
Does not change infoset of XML document
Two flavors:
The standard XML syntax
RNC (RelaxNG Compact)

4. The RNC Schema Proposal
In a nutshell:
The nominative XDI schema language is RelaxNG Compact Syntax
As a convenience to implementors we provide:
W3C Schema translation of each XDI schema
A RelaxNG XML schema translation as well
The naming convention be xdi-VNN.rnc, xdi-VNN.rng, xdi-VNN.xsd
XDI extension schemas would be xdi-extname-VNN.xxx

5. The RNC Schema for XDI
default namespace xdi = "
namespace local = ""
datatypes xsd = "
start = resource
resource = element Resource { xriset, resource*, ref*, backref*, link*, ( data | xmlresource )* }
link = element Link { xriset, ref+ }
backref = element Backref { xri, backref* }
ref = element Ref { xri }
data = element Data { mixed { ref+ | anyElement* } }
xriset = element XRISet { authority*, type*, instance* }
xri = element XRI { authority?, type?, instance? }
authority = element Authority { text }
type = element Type { text }
instance = element Instance { text }
xmlresource = element XMLResource { xmlheader, xmldata }
xmlheader = element XMLHeader { foreignAttribute*, anyElement* }
xmldata = element XMLData { foreignAttribute*, anyElement*}
xmlref = element XMLData { att.uri?, xmltransforms? }
xmltransforms = element XMLTransforms { xmltransform+ }
xmltransform = element XMLTransform {att.algorithm, (foreignElement | xpath )* }
xpath = element XPath { xsd:string }
att.algorithm = attribute Algorithm { xsd:anyURI }
att.uri = attribute URI { xsd:anyURI }
foreignElement = element * - xdi:* { (anyAttribute | text | anyElement)* }
foreignAttribute = attribute * - (xdi:*|local:*) { text }
anyElement = element * { (anyAttribute | text | anyElement)* }
anyAttribute = attribute * { text }

6. Benefits Allows us to support all the major schema languages
Easier to read and modify
More efficient parsing
Less of a learning curve

7. The Top Reason Backwards compatibility
RelaxNG is capable of validating multiple versions of the same schema, W3C schema is not with multiple passes
The speed at which we are implementing software and developing XDI means allowing vendors to support multiple versions of the XDI schema is IMHO not just desirable, but crucial to our success.