XLink: Open Linking Standard XML / XSL separate  data semantics  presentation semantics Need to also separate out  navigation semantics Single unique feature of the Web  hypertext link

XML: Linking By Explicit ID XML & SGML provide simple linking  ID / IDREF combination Buy me a Shrek Soundtrack Only works in same document

HTML: Cross-Document Linking HTML adds cross-document named element linking Buy me a present Shrek Soundtrack 25.99

Linking: Pointing and Clicking A link embodies a relationship A link must specify  the items taking place in the relationship  the meaning of the relationship  the user interface for the link Need standards for each of these

XPointer Addressing XLink adds location language XPointer  simple id-based addressing  XPath addressing  stepwise addressing Dear Father Christmas, Here is what I want

Further XPointer Addressing Simple sub-element content addressing  #xpointer(string-range(/1/6/4,'Leslie Carr')) Ranges  #xpointer(id("sec2.1") range-to id("sec2.4"))

XLink Structures Links have  locators – identify the resources  arcs – specify the connections between resources  title – description of a link / arc for a human  role – description of a link / arc for a computer

HTML Link = XML Simple Link Intelligence, Agents and Multimedia href the link embedded in a document. Its contents form part of the document

XML Extended Link Names in RED are part of the XLink namespace the extended link may be stored in a database. Its contents DON’T form part of the of any document locator href arc to from

XLink Behaviour Links can be triggered ( actuate attribute)  by user clicksuser  by the applicationauto Links can be displayed ( show attribute)  in another windownew  in the current windowreplace  instead of the current element embed

XLink Recap Simple links involve the current resource and one other (like … ) Extended links may involve many resources  no longer source and destination  each link end has a title and role Links may appear out of line, even in a linkbase

Using Linkbases Linkbases  are collections of links  can be swapped, allowing different links on same resources Amazon linkbase IMDB linkbase

Generic Links Generic links are not limited in scope to a single document  usually expressed as a content-based query keyword citation aka smart tag  used for glossary purposesglossary purposes

Resource-based Authoring Linkbases + generic links improve flexibility Resource-based authoring is the natural authoring paradigm of an open hypermedia* system  create a set of independent resources  integrate them using sets of link databases * See later lectures

Resource-based Authoring Lecture 1 Lecture 2

Resource-based Authoring Lecture 1 Lecture 2 Toolbook Simulation Video Sequence

Resource-based Authoring Lecture 1 Lecture 2 Toolbook Simulation Video Sequence Tutorial Links #1

Resource-based Authoring Lecture 1 Lecture 2 Toolbook Simulation Video Sequence Tutorial Links #1 Tutorial Links #2

Resource-based Authoring Lecture 1 Lecture 2 Toolbook Simulation Video Sequence Tutorial Links #1 Glossary Links Glossary Documents Tutorial Links #2

Resource-based Authoring Note that the creation of the content (web pages, videos, simulations etc) is INDEPENDENT of the creation and deployment of the links THANKS TO the use of a separate linking process

Resource-based Authoring Adapt the integrated information resource for different audiences by  Using different linkbases  Chosen according to user profile e.g.  simple explanatory links for first year undergraduates  vs links to in depth reading and further challenges for PhD students

DLS: A Linking Service Distributed Link Service  developed in IAM group (predates XLink)  independent service providing linking  maintains separate databases of links  merges them with documents on the fly Uses two linking forms  explicit (positional) addressing  implicit (content-based) linking

DLS Architecture Publishers' linkbases Keyword linkbases Proxy Hyper link Agent XLink linkbases User profiles Person Agent Citation Agent Bibliography database IR Agent Inverted index Ontology Agent Web Browser Web Server

DLS Example DLS Server’s View User’s View

Collections of links to include while browsing Options for presenting links. What should a link look like? What should a link do when you click it? Only display important links, or use colour to highlight them.

DLS Styles Pristine original document Document + plain link style Bibliographic link style Link priorities distinguished by colour scheme.

DLS Behaviours Click here and choose from lots of different destinations here Clicking on links adds them to a link notepad so that you can finish reading this page before you go to another one! Pending Links

DLS and XLink DLS ‘knows about’  citations, people etc  formatting and behaviour semantics XLink has no knowledge  meaning of contents  meaning of presentation semantics

XLink Future Not yet implemented widely Needs to be tied in with XML processing model  Provide extra info to XSL about things that are link anchors (XML Link InfoSet?)  Define position in processing After entities are resolved Before stylesheet is invoked If some text is transcluded, what is its URL?