Abstract

XLink's data model allows a number of combinations of XLink placement, XLink encoding, and XLink structure which make it hard to get an overview of all possible usages. XLink characterization aims at systematically looking at the various placements, encodings, and structures XLink allows, as well as looking at the individual participating resources of the link and their characterization in terms of their properties and their connections with the other resources participating in the link.

XLink Analyzer

XSLT 1.0 program for analyzing links
- link classification according to Link Phenomenology
- resource classification according to Resource Phenomenology (only partly)
Analyzing this blinkbase result in this XLink analysis
- the blinkbase contains just two posts from the Doc or Die Blog

 <xsl:param name="linkbase" select="''"/>
 <xsl:template match="/">
  <html>
   <head>
    <title>XLink Analyzer</title>
    <style type="text/css">*:target { outline : red solid medium ; }</style>
   </head>
   <body>
    <xsl:apply-templates select="/" mode="link-analyzer"/>
   </body>
  </html>

Outline (Link Phenomenology)

Link Phenomenology [11]
1. Link Types [3]
2. Link Location [4]
3. Link Occurrence [4]
Resource Phenomenology [3]
Conclusions [1]

Outline (Link Types)

Link Phenomenology [11]
1. Link Types [3]
2. Link Location [4]
3. Link Occurrence [4]
Resource Phenomenology [3]
Conclusions [1]

Simple vs. Extended

Simple Links use a small set of attributes (and nothing but attributes)
Extended Links are based various XLink element types being used together
XLink element types are identified by the type attribute
Extended Links can have a number of children
- resources contain a resource as inline information (like the source of a)
- locators identify a resource through a URI (like the target of a)
- arcs carry Behavior Attributes and connect resources through Traversal Attributes
- titles carry title information (and are repeatable and thus can be used for internationalization)

Simple Link: Type S

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:xlink="http://www.w3.org/1999/xlink">
 <head>
  <title>XLink Type S</title>
 </head>
 <body>
  <h1>XLink Type S</h1>
  <p>This is a <span xlink:type="simple" xlink:href="http://dret.net/">Type S XLink</span>.</p>
 </body>
</html>

Extended Link: Type E

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:xlink="http://www.w3.org/1999/xlink">
 <head>
  <title>XLink Type E</title>
 </head>
 <body>
  <h1>XLink Type E</h1>
  <p>This is a <span xlink:type="extended">
    <target xlink:type="locator" xlink:href="http://dret.net/" />
    <anchor xlink:type="resource">Type E XLink</anchor>
   </span>.</p>
 </body>
</html>

Outline (Link Location)

Link Phenomenology [11]
1. Link Types [3]
2. Link Location [4]
3. Link Occurrence [4]
Resource Phenomenology [3]
Conclusions [1]

Inline vs. Out-of-Line

XLinks can be used inline or out-of-line
- this does not change a link's semantics
- inline placement may be appropriate for smaller links
- more complex links are not very convenient when used inline
Inline XLinks cannot be used for all XLinks
- linking from complete resources cannot be done with inline links
- linkbases are only possible with out-of-line links
Out-of-line XLinks can be used for all XLinks
- every inline XLink can be replaced by an out-of-line XLink
Simple links are always inline links
- one of the participating resources is the content of the simple link
- the other resource is pointed to with the href attribute

Simple Inline Link: Type S/i

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:xlink="http://www.w3.org/1999/xlink">
 <head>
  <title>XLink Type S</title>
 </head>
 <body>
  <h1>XLink Type S</h1>
  <p>This is a <span xlink:type="simple" xlink:href="http://dret.net/">Type S XLink</span>.</p>
 </body>
</html>

Extended Inline Link: Type E/i

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:xlink="http://www.w3.org/1999/xlink">
 <head>
  <title>XLink Type E</title>
 </head>
 <body>
  <h1>XLink Type E</h1>
  <p>This is a <span xlink:type="extended">
    <target xlink:type="locator" xlink:href="http://dret.net/" />
    <anchor xlink:type="resource">Type E XLink</anchor>
   </span>.</p>
 </body>
</html>

Out-of-Line Link: Type E/o

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:xlink="http://www.w3.org/1999/xlink">
 <head>
  <title>XLink Type E/o</title>
  <link xlink:type="extended">
   <target xlink:type="locator" xlink:href="http://dret.net/" />
   <target xlink:type="locator" xlink:href="#link" />
  </link>
 </head>
 <body>
  <h1>XLink Type E/o</h1>
  <p>This is a <span id="link">Type E/o XLink</span>.</p>
 </body>
</html>

Outline (Link Occurrence)

Link Phenomenology [11]
1. Link Types [3]
2. Link Location [4]
3. Link Occurrence [4]
Resource Phenomenology [3]
Conclusions [1]

Embedded vs. Linkbase

Out-of-line links must always be integrated for rendering
- they are not situated at the location which they are linking
Out-of-line links can be retrieved from various sources
1. from the document itself (appearing in some metadata location)
2. from a linkbase which the document author points to
3. from a linkbase which the document user points to
Document users must have some means of specifying a linkbase
- AJAXLink allows this by using the extension to connect to linkbases
- another possibility would be to to this using a bookmarklet

Embedded Link: Type E/o/e

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:xlink="http://www.w3.org/1999/xlink">
 <head>
  <title>XLink Type E/o</title>
  <link xlink:type="extended">
   <target xlink:type="locator" xlink:href="http://dret.net/" />
   <target xlink:type="locator" xlink:href="#link" />
  </link>
 </head>
 <body>
  <h1>XLink Type E/o</h1>
  <p>This is a <span id="link">Type E/o XLink</span>.</p>
 </body>
</html>

Linkbase: Type E/o/l

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:xlink="http://www.w3.org/1999/xlink">
 <head>
  <title>XLink Type E/o/l</title>
  <linkbase xlink:type="extended">
    <startrsrc xlink:type="locator" xlink:label="spec" xlink:href="." />
    <linkbase xlink:type="locator" xlink:label="linkbase" xlink:href="xlink-type-E-o-l-linkbase.xml" />
    <load xlink:type="arc" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:from="spec" xlink:to="linkbase" actuate="onLoad" />
  </linkbase>
 </head>
 <body>
  <h1>XLink Type E/o/l</h1>
  <p>This is a <span id="link">Type E/o/l XLink</span>.</p>
 </body>
</html>

<linkbase xmlns:xlink="http://www.w3.org/1999/xlink">
 <link xlink:type="extended">
  <target xlink:type="locator" xlink:href="http://dret.net/"/>
  <target xlink:type="locator" xlink:href="xlink-type-E-o-l.html#link"/>
 </link>
</linkbase>

Third-Party Linkbase: Type E/o/l3

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:xlink="http://www.w3.org/1999/xlink">
 <head>
  <title>XLink Type E/o/l3</title>
 </head>
 <body>
  <h1>XLink Type E/o/l3</h1>
  <p>This is a <span id="link">Type E/o/l3 XLink</span>.</p>
 </body>
</html>

<linkbase xmlns:xlink="http://www.w3.org/1999/xlink">
 <link xlink:type="extended">
  <target xlink:type="locator" xlink:href="http://dret.net/"/>
  <target xlink:type="locator" xlink:href="xlink-type-E-o-l3.html#link"/>
 </link>
</linkbase>

Outline (Resource Phenomenology)

Link Phenomenology [11]
1. Link Types [3]
2. Link Location [4]
3. Link Occurrence [4]
Resource Phenomenology [3]
Conclusions [1]

XLinks Link Anything

XLinks are an XML syntax for hypermedia links
- the participating resources can use any MIME type
- fragments of resource can use any fragment identifier
It is impossible to reliably determine the type of a URI-identified resource
- this is a feature of the Web (enabling HTTP Content Negotiation)
- guessing the content type is possible but should be done with care
XLink rendering can become very resource-intensive
- retrieve (at least access) all participating resources to determine their media type
- render only those links which can be handled by the implementation
- for specific scenarios (such as blinks) this can be handled more efficiently

MIME Types

<html xmlns="http://www.w3.org/1999/xhtml" xmlns:xlink="http://www.w3.org/1999/xlink">
 <head>
  <title>XLink Type E/o</title>
  <link xlink:type="extended">
   <!-- the following uri assumes an image fragment identifier of rect(startx, starty, sizex, sizey) -->
   <target xlink:type="locator" xlink:href="../img/lookoflink-xlink-mockup.jpg#rect(202,137,154,174)" />
   <target xlink:type="locator" xlink:href="http://w3.rz-berlin.mpg.de/cmp/beethoven_sym5_1.mp3" />
   <target xlink:type="locator" xlink:href="http://en.wikipedia.org/wiki/Symphony_No._5_(Beethoven)" />
  </link>
 </head>
 <body>
  <h1>XLink Type E/o</h1>
  <p>An image with music and text link: <img src="../img/lookoflink-xlink-mockup.jpg" /></p>
 </body>
</html>

Fragment Identifiers

Fragment identifiers are always specific for a resource type
- they are a client-side issue only (the HTTP request retrieves the complete resource)
- depending on the type and fragment, different interfaces can be implemented
Some XLink semantics may be hard to interpret meaningfully
- embedding an image into a HTML page has become second nature for Web authors
- embedding fragments of images in HTML already is far more exotic in nature
- embedding HTML into a fragment of an image is probably too exotic
- embedding between temporal and non-temporal media types probably always is problematic

Outline (Conclusions)

Link Phenomenology [11]
1. Link Types [3]
2. Link Location [4]
3. Link Occurrence [4]
Resource Phenomenology [3]
Conclusions [1]

Link Complexity

Comparing URIs is not a string comparison
Media types are dynamic and can be negotiated
Arc semantics depend on default arcs being used
Make sure to document what the implementation does!

XLink Characterization

Web-Based Publishing (INFO 290-19)

Erik Wilde, UC Berkeley School of Information
2007-03-08

Abstract

XLink Analyzer

Outline (Link Phenomenology)

Outline (Link Types)

Simple vs. Extended

Simple Link: Type S

Extended Link: Type E

Outline (Link Location)

Inline vs. Out-of-Line

Simple Inline Link: Type S/i

Extended Inline Link: Type E/i

Out-of-Line Link: Type E/o

Outline (Link Occurrence)

Embedded vs. Linkbase

Embedded Link: Type E/o/e

Linkbase: Type E/o/l

Third-Party Linkbase: Type E/o/l3

Outline (Resource Phenomenology)

XLinks Link Anything

MIME Types

Fragment Identifiers

Outline (Conclusions)

Link Complexity

XLink Characterization

Web-Based Publishing (INFO 290-19)

Erik Wilde, UC Berkeley School of Information2007-03-08

Abstract

XLink Analyzer

Outline (Link Phenomenology)

Outline (Link Types)

Simple vs. Extended

Simple Link: Type S

Extended Link: Type E

Outline (Link Location)

Inline vs. Out-of-Line

Simple Inline Link: Type S/i

Extended Inline Link: Type E/i

Out-of-Line Link: Type E/o

Outline (Link Occurrence)

Embedded vs. Linkbase

Embedded Link: Type E/o/e

Linkbase: Type E/o/l

Third-Party Linkbase: Type E/o/l3

Outline (Resource Phenomenology)

XLinks Link Anything

MIME Types

Fragment Identifiers

Outline (Conclusions)

Link Complexity

Erik Wilde, UC Berkeley School of Information
2007-03-08