Goal and History

Provide more advanced (hyper)linking functionnalities to XML based applications:

• Extensive and robust pointing within an XML document
• Advanced and versatile linking mechanism

History:

• Was done in the initial XML WG => March 98 WD
• A new WG was created in September
• Published it's requirements 24 Feb 1999
• Decided to merge the Pointing syntax with XSL pattern matching

The Working Group

The Bazaar !

• Old SGML establishment (Arbortech, Steven DeRose, Murray), Tim Bray left
• Microsoft, IBM, Fujitsu, Oracle, Sun)
• New comers: Commerce One, RogeWave, ImmediateDigital
• Steven DeRose was initially the unique editor
• And a completely over commited chair, bill Smith (Sun)

Current State

• The group is late, but recovering slowly
• The editor pool has been increased
• Unification with XSL is done, XPointer looks stable
• The WG plan to release XPath and XPointer to public on 12 of July
• Strong debate over XLink, generic Linking vs. HyperLinking, and simplification
• Updated requirements are on the way too

Technical overview

XPath quick description

XPath describes the syntax and associated processing to select groups of nodes and attributes within an XML document tree.

25 pages.

• powerful, very complex searches can be build
• Expression language for XML trees
• Uses selection axis to build the search semantic
• Can be extended in a given context (variables, functions).
• Has an abbreviated syntax

XPointer

XPointer build on top of XPath and add the following:

• A schema mechanism #xptr(...), could possibly be cascaded
• Ranges: to be able to point to contiguous sets of nodes
• String: to be able to select strings, not only full nodes
• Absolute path: / (root), id(), here() and origin()

basically what is needed to be able to express a selection

XPointer disable variables supports in XPath

XPointer Examples

• id(intro)/p

  all <p> child nodes of the element ID="intro"

• //chapter[title="Introduction"]

  all the chapter elements having a child title of content "Introduction"

• id(intro)/range{child(1),fsibling(2)}

  first through third children of ID=intro

• /chapter[1]/p[2]/string(2, "W3C", 2)

  select the position of the '3' in the 2nd occurence of "W3C" in the second paragraph of the first chapter.

XLink

The current XLink draft is smaller (15 pages), linking properties can be defined using linking elements or adding linking specific attributes to existing elements.

Linking cababilities covers a wide spectrum:

• Simple links: one locator (target) only.
• Extended links: allow multiple locator and outline links

Semantic of liking is refined with attributes:

• Locator
  • href: a single target
• Arcs
  • from: outline link definition, the source
  • to: destination of the link, the target
• Behavior
  • show: how to render a link traversal: new, parsed or replace
  • actuate: how to trigger the link traversal: user or auto
• Semantic
  • role: generic string for describing the relationship
  • title: human readable description of the link.

XLink Simple Links Examples

A simple link on an user-defined element

<A xlink:type="simple" xlink:href="http://www.w3.org/TR/wd-xlink/"
 xlink:title="The Xlink Working Draft">The XLink Working Draft.</A>

A simple link using the predefined element

<xlink:simple href="http://www.w3.org/TR/wd-xlink/"
title="The XLink Working Draft">The XLink Working Draft</xlink:simple>

The same with all attributes

<xlink:simple href="http://www.w3.org/TR/wd-xlink" role="working draft" 
         title="The XLink Working Draft" show="replace" actuate="user">
	  The XLink Working Draft.</xlink:simple>

XLink Extended Links Examples

An extended link using the predefined element

<xlink:extended role="address book" title="DV's Address Book"
     showdefault="replace" actuatedefault="user"> 
  <xlink:arc from="http://www.redhat.com/#xptr(/search[1])"
       to="http://rpmfind.net/linux/RPM">My search engine</xlink:arc>
</xlink:extended>

An extended link on an user-defined element

<foo xlink:type="extended" role="address book" title="DV's Address Book"
     showdefault="replace" actuatedefault="user"> 
  <xlink:arc from="http://www.redhat.com/#/search[1]"
       to="http://rpmfind.net/linux/RPM">My search engine</xlink:arc>
</foo>

XArc proposal

The XArc proposal was done by Gabe Beged-Dov before he joined the WG, his rationales are to simplify the syntax, and move toward an RDF like modelling of links. The debate in the IG list generate quite some heat.

The working group accepted to add Arcs support in the draft, but the minimalists now want to get rid of the "old stuff" ...

A cleaner spec sounds nice, the problem is that the ancient still have control and this doesn't really help the WD publication schedule.

XArc examples

<LoopArc  xarc:from="#this()" xarc:to="#this()" > I'm a self-absorbed arc
</LoopArc>

<EmbeddedToArc  xarc:from="id(SomePlace)"  xarc:to="#this()" > We're already
    there! 
</EmbeddedToArc>

<EmbeddedFromArc  xarc:from="#this()" xarc:to="id(SomePlaceElse)" > Follow me
    to the destination 
</EmbeddedFromArc>

Other controversial stuff

There is still IMHO a bunch of serious issues:

• in the case the behaviour is defined as predefined attributes values in an External DtD, the lik will be detected (or handled properly) only if the Dtd is fetched and parsed.
• Introducing an XSL style sheet lead to dual infoset for a single document, which one should be used for XPtr and XLink ? Behaviour of linking would be directly dependant on XSL support ! MS take this as a good opportunity to get the competition out, and fast !
• The schedule for XLink WD publication
• Bill Smith called for a co-chair help, no answer so far ...

I'm still hoping we will get to REC for Fall.