Hypertext functionalities and XML

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Hypertext functionalities and XML
Fabio Vitali ltfabio_at_cs.unibo.itgt Dept. of
Computer Science University of Bologna
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Important notice

• The proceedings have a heavily mangled version of
  this paper.
• The CD has both the HTML and the PDF version
  correct.
• At the coffee break new printed copies will be
  available. Please get one.

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Introduction

• Hypertext functionalities are the distilled
  wisdom of the hypertext field.
• Most of them are now possible on the World Wide
  Web, but only through custom-made hacks and
  tricks. Not really possible in a widespread way.
• XML, XPointers and XLinks can be used to
  implement most of them.

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Hypertext functionalities on the Web

• Typed nodes and links
• Link attributes and structure-based queries
• Transclusions, warm and hot links
• Annotations and public vs. private links
• Computed personalized links
• External link databases and link update
  mechanisms
• Global and local overviews
• Trails and guided tours
• Backtracking and history based navigation
• These items were selected from a longer list
  assembled at the 2nd HTF workshop (Hypertext'96
  conference)

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A prototype of an XML document browser

• XML for representing notations
• The architecture of displets
• Some applications of displets

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XML for representing notations

• XML is a relevant advancement over HTML and other
  similar languages.
• XML supports structure.
• XML allows authors to define new DTDs (or DTD
  chunks) for describing arbitrary needs in terms
  of notations and structure
• XML supports sophisticated hypertext links.
  Multiple destinations, transclusions, typed links
  are all possible. External links allow to create
  external link bases.
• There is just one problem with XML XSL is not up
  to XML in terms of generality specialized
  notations are not supported.

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Displets

• Our proposal is to create an open set of
  formatting objects that are loaded when needed,
  depending on the content of the document.
• Each document would have a stylesheet associated
  that maps the document elements into the
  available formatting objects.
• Each formatting object would then be associated
  to a software module (that we call displet) that
  displays the information in some way. The dynamic
  linking capabilities of Java are extremely
  helpful for this.

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Displets for HTML
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XMLC

• We have designed and created a prototype for
  rendering displets

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An XML browser
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Some applications of displets

• Typographical elements
• Notations for software engineering
• Active documents

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Typographical elements

• We have created displets supporting very simple
  text-based elements
• Paragraphs and lists
• Inline elements
• Images
• Simple and multi-directional links
• Layout management

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Text-based displets
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Layout management
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The Z notation (1)

• ltschemadef style"vert" purpose"state"gt
• PhoneDB
• ltdecpartgt
• ltdeclgt_knownpsetNAMElt/declgt
• ltdeclgtphone NAME fpfun PHONElt/declgt
• lt/decpartgt
• ltformalsgt K,L,Z lt/formalsgt
• ltaxpartgt
• ltpredicategtknown dom phonelt/predicategt
• lt/axpartgt
• lt/schemadefgt

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The Z notation (2)
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Active documents

• A "passive" document is just content and
  presentation.
• An "active" document provides support for action
  on the document it can include animations,
  perform computations, provide support for
  searching etc.
• Active-X objects, Java applets, JavaScript
  scripts or even complex PostScript programs can
  be used to have documents "be" more than their
  content
• Usually there is a clear difference between the
  content and the code different syntax, different
  place in the document, different working
  paradigm.
• Our approach is more radical, in that we use
  generic markup behaviors and actions are applied
  just like formatting

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Declaratively active documents

• The architecture of displets can be applied to
  have documents perform activities, rather than
  just be displayed.
• Since we associate Java Beans to XML elements, we
  can ask these classes to paint themselves, or to
  perform another method of their classes.
• Depending on the stylesheets and the Java
  classes, then, the same document can behave in
  any number of different ways
• The code performing the activities is not part of
  the document (as in Active X or similar methods),
  but declaratively associated to the document.

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ToolBook (1)

• A ToolBook book is composed of active objects in
  complex inter-relationships among them.
• Text fields, buttons, images, books and pages may
  have associated scripts (in Toolscript) and can
  be used to create sophisticated applications.
• We have created a WWW browser environment for
  ToolBook books.
• The book is converted into an XML document, and
  Java classes for the elements are available text
  fields, buttons, pages and images.
• Support for Toolscript, Javascript and different
  methods of message passing are also provided

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ToolBook (2)
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Finite State Machines (1)

• ltStateMategt
• LEVEL_MANAGER_CONTROL
• ltState id"state1" start"true"
  origin"0,50"gtWAITlt/Stategt
• ltState id"state2" origin"250,50"gtNEW_VALlt/Stat
  egt
• ltState id"state3" end"true"
  origin"100,200"gtPUMP_ACTIVElt/Stategt
• ltArc from"state2" to"state1"gtLM_ACTIVElt/Arc
• ltArc from"state1" to"state3"gtLM_MORElt/Arcgt
• ltArc from"state3" to"state2"gtUPDATElt/Arcgt
• lt/StateMategt

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Finite State Machines (2)
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Petri Nets
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Specifications in UML (1)

• The Unified Modeling Language is a fast-spreading
  language for O-O design of systems.
• It is made of several rendering notations, with a
  way to express internal consistency constraints.
  
• We are creating displets to display the UML
  specifications, and plan to perform some static
  analysis on them.
• The same document will therefore have different
  actions associated to it, e.g., for display,
  conversion, and verification.

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Specifications in UML (2)
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Hypertext functionalities and XMLC

• Most of the hypertext functionalities can be
  provided using XPointers and XLinks and a generic
  mechanism for notations.
• The support for XPointers and XLinks has been
  added to XMLC, by introducing two new steps in
  the transformation of the document.
• An important issue is the maintenance of the
  identity and identificability of link elements
  after XSL transformations.

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XPointers and XLinks in XMLC
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The XLink-enabled browser
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Other activities with XMLC

• An implementation of 80 of XSL-FO
• A limited integration with Mozilla
• Musical scores
• Train schedules

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Conclusions

• The WWW is now too complex for large-scale
  deployment of sophisticated hypertext
  functionalities.
• The simplification of WWW protocols and languages
  brought by XML should considerably improve the
  situation, but...
• The Web architecture itself must evolve to
  incorporate these functionalities on a
  sufficiently large scale.
• XMLC is just a prototype, but I.E. 5.5 should
  already be offering most of the same
  functionalities on a much larger scale.

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Open issues

• Establishing a widespread architecture for
  modules implementing formatting objects.
• Co-existence of independently created modules
  (just leaves or also containers?)
• Independence of architecture

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Displets project home page

• http//www.cs.unibo.it/projects/displets

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Important notice (again)

• The proceedings have a heavily mangled version of
  this paper.
• The CD has both the HTML and the PDF version
  correct.
• At the break new printed copies will be
  available. Please get one.