Compound Documents and Web Applications

W3C Workshop

San Jose, CA, 1-2 June 2004

Steve Zilles, Independent Consultant

My Background

• I am a document guy
  rather than a Web App guy
• 20 years of working with documents
• Most recently as co-chair for XSL 1.0
• But also worked on HTML and CSS

Facilitating Compound Documents
Means
Facilitating Interacting Applications

• Compounding means having many types
  • text, graphics, math, chemical formulae, ...
• Typically no one product supports them all
• Authors need different subsets
• Vendors support yet different subsets
• Implication:
  • Find way to support a mix of components

Requirements
for Mixing Components

1. Property Propagation
2. Event Propagation
3. Formatting/LineBreaking Model
4. Timing and Animation Propagation
5. Spell Check
6. Search
7. Accessibility

An example: Property Propagation

An interface that, Given a property, provides:

• an API
  to ask for the computed value for that property
• an API
  to ask whether that property is inherited.
• an API that allows the embedded processor to indicate what properties the embedded processor may be interested in.

A Question:
What/Who is in Charge?

Which "document"?

• SMIL - because of timing considerations
• XHTML - because that is the document
• SVG - because it has more for layout
• XForms - because it has interaction

Which capability provider?

• The Operating System
• The Browser
• A Platform Independent Virtual Machine

What Then Should Happen?

A two pronged approach

1. a practical combination
2. a practical virtual machine

The Practical Combination

A combination of XHTML, SVG, SMIL, ...

Reasons

• has immediate utility
• works out
  • the problems of interaction for a fixed set of components
  • what should be specified; what should not (e.g. Save/Restore)

Should have no assumption that any one component is in charge

Experience here and elsewhere leads to

The Practical Virtual Machine

• Not the answer to all the worlds problems
• But, does allow combination of arbitrary components

• Benefit from the experience of application builders
• Time to abstract from what has been learned

What then should be provided?