Schemas and Encoding Rules

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Schemas and Encoding Rules
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XSD to ASN.1

• X.694 defines a standardized mapping from XSD to
  ASN.1
• Software tools can make mapping transparent
• Developer only needs to work with one schema
  language.

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XSD to ASN.1 (contd)
X.694
XSD
ASN.1
schema
encoding
XML
BER orPER
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ASN.1 Basic Encoding Rules

• Uses a tag-length-value (TLV) format

TAG
LEN
VALUE
TAG Binary Identifier LEN Length in
bytes VALUE Binary Content
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ASN.1 BER (contd)

• TLV structure must be maintained throughout
• Value for a TLV may be other TLVs
• Can use indefinite length to wrap TLVs for
  streaming transfers

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BER versus XML

• Both use tags to identify contentXML
  lttaggtvaluelt/taggtBER tag / length / value
• XML tag and value are textual whereas BER tag and
  value are binary.
• Both allow hierarchal, tree-like structures to be
  built.

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BER versus XML (contd)

• BER optimizes XML in 2 ways
• 1. Reduction of metadata through use of binary
  tags, and
• 2. Storing of binary message content in binary
  form (i.e. no conversion to base64)

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Why consider it for EXI?

• Already standardized
• Mature and stable
• Provides relatively compact binary format
• High performance
• Relatively simple similar to XML in concept.

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Negatives

• The A word
• Not the most compact format.BUT can zip entire
  message (ala XBSC)- or - (better yet)can zip
  select Vs within message(compartmentalization)

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Negatives

• Schema dependentHowever there is a defined
  structure (TLV) that can be interpreted to some
  degree without schema. Would either need to
  package schema with message for standalone or use
  some other format (for example, FI)

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Negatives

• Bad press because of security issues
• May actually be a positive Issues are known.
  Experience with format extensive test suites
  (OULU, NISCC) make it possible to implement
  secure applications.
• A new format will be subject to these problems
  again.

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UBL Invoice Message Sizes

• Larger message with a large amount of markup
• XML 8284 bytes
• BER 1098 bytes
• PER 786 bytes