XML Infosets

1. XML has grown
2. What is the Infoset?
3. What does it mean to be “abstract”?
4. Infoset details
5. Overview of InfoSets
6. Infosets can change (“Infoset Pipeline”)

XML has grown

• It has produced:
  • XML the language
  • Namespaces
  • XSLT/XPath/DOM
  • XLink/XPointer
  • Canonical XML, XML Signature
  • XML Query, XML Protocols
  • and the list is getting longer and longer…
• XML 1.0 did not define its own data model; so…
  • XPath had to define its own…
  • then Xlink had to define its own…
  • then DOM had to define its own…

What is the Infoset?

• An abstract data model for XML 1.0 plus Namespaces
• What is an “abstract data model”?
  • the “thing” that a sequence of start tags and attributes and character data represents
  • A formalization of our intuition of what it means to “be the same document”
  • The thing that is common to all the uninterestingly different ways of representing it
    • single or double quotes
    • whitespace inside tags
    • general entity and character references
    • alternate forms of empty content
    • specified vs. defaulted attribute values

What does it mean to be “abstract”?

• The Infoset is a description of the information in a document
• A vocabulary to express requirements on XML applications
• It’s a bit like numbers as opposed to numerals
• The Infoset is not:
  • the DOM (much higher level)
  • about implementation or interfacing at all
• But you can think of it as a kind of fuzzy data structure
• (if that helps)

Infoset details

• Defines a modest number of information items:
  • element, attribute, namespace declaration, comment, processing instruction, document…
• Each one is composed of properties
  • which in turn may have information items as values
• Examples for the properties:
  • element and attribute information items have [local name] and [namespace URI]
  • element information items have [children] and [attributes]
  • attribute information items have [normalized value]
  • processing instruction items have a [target]
  • comment items have a [content]
  • etc.

Overview of InfoSets

Infosets can change (“Infoset Pipeline”)

• Infosets describe the action of other XML operations
  • XML Parser builds an Infoset from a character stream (or an application produces an Infoset from somewhere else)
  • a validating parser builds a richer Infoset: eg, defaulted values, ignorable whitespace
  • XML Schema validates the Infoset and adds new properties: eg, type references
  • XSLT transforms an Infoset into another
  • XInclude (proposal) merges Infosets
  • The Infoset is accessed by XML Query
  • XML Protocol parcels information items for transmission
  • etc.
• It unifies various XML Applications!