Efficient XML Interchange

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Efficient XML Interchange

• What is it?Why is it?How does it fit in?

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What is Efficient XML Interchange?

• Alternative Representation of XML Infoset
• support full XML (Infoset) data model
• not a subset
• no really, not a subset!
• Interchange Format
• optimized for data exchange
• transmission, storage, processing
• can use Schema, conventional compression

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Why?

• Expand the Web
• limited uptake of XML friends in certain
  domains
• performance is problem
• noteworthy domains
• mobile, embedded, scientific,
• Lesson From Binary XML Formats
• real need, and real solutions
• widely applicable, win-win
• multiple formats cause segregation, limit adoption

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Integration into XML Stack

• Same Data Model
• merely an alternative encoding
• Open Issues
• format, or encoding?
• content negotiation?
• schema knowledge vs content negotiation
• modes, configurability (e.g. simple types)

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WebAPI / EXI?

• Impact on
• APIs
• initalisation encoding modes, schema info?
• XMLHttpRequest
• again modes, schema info?
• diversity of formats?
• Are data models in sync?
• HTML as XML?
• REX
• fragment support?

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Efficient XML Interchange

• Format Basics

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Efficient XML Interchange

• Goal(s)
• maintain XML (Infoset) data model
• seamless integration into XML software stack
• improve compaction AND processing
• Observation
• smallness has multiple benefits
• e.g. energy consumption during transmission
• allows XML deployment in new scenarios
• Underlying Philosophy
• exploit a-priori knowledge of (likely) content

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How does it work?

• Exploit Knowledge, at Several Different Levels
• XML knowledge
• copious syntactic redundancy
• Schema knowledge
• schema describes content in detail
• heuristics
• e.g. (declared) elements gtgt processing
  instructions
• e.g. repeated string elements
• e.g. small numbers gtgt large numbers
• Cooperation with Conventional Compression
• heavily biased data stream as compressor input

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EXI Base Format

• Coding Grammars
• generic grammar describe full XML Infoset
• arbitrary elements, PIs, comments, entity
  references, etc.
• schema-derived grammar
• describes a specific format
• content-derived grammar
• add rules depending on encountered elements
• splice these together, at very fine granularity
• allow anything, but know what is (currently)
  likely
• likely content more efficient encoding

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EXI Base FormatBuilt-in, Generic Element Grammar
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EXI Base FormatA Schema-Based Grammar

• Element Content Model
• (optional) attribute color
• (optional) element desc
• (mandatory) elements quantity, price

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EXI Base FormatMerged Generic Schema Derived
Grammar
SE(quantity)
SE(price)
SE(quantity)
SE(desc)
SE(), CH, ER, CM, PI
SE(), CH, ER, CM, PI
SE(), CH, ER, CM, PI
EE
EE
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Other, Major EXI Features

• Simple Type Values
• optimized codecs
• type assigment through grammar
• generic text coding always available
• string / value tables
• Bit-Packed vs byte-aligned codec
• biased input into deflate compression

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Impact on the XML Stack

• Questions
• content negotiation, header
• http integration?
• what do you need? what would be a problem?
• pre-shared schemas
• which formats? samples?
• (X)HTML? AJAX?
• need hooks in the specification?
• options / variables
• different schemas, different options?