VTD-XML: The Future of XML Processing

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 A Quick Overview on Virtual Token Descriptor

  • It is a binary format specification, not an API specification
  • A VTD record is a primitive data type  (integer multiple of 32 bits) that encodes the following parameters of a token in an XML file: 
    • Starting offset 
    • Length
    • Nesting depth
    • Token type 
  • VTD requires that XML document be maintained intact in memory.
  • Our current VTD record layout further specifies the following:
    • Use 64 bits as the primitive type (b63~b0)
    • Big endian
    • Starting offset: 30 bits  (b29 ~ b0)  maximum value is 2^30 -1 = 1G -1
    • Length: 20 bits (b51 ~ b32) maximum value is 2^20-1 = 1M -1
      • For some token type
        • Prefix length: 9 bits (b51~ b43)   max value 511
        • Q-name length: 11 bits (b42 ~ b 32)  max value 1023
    • Depth: 8 bits (b59~b52) max value is 2^8-1 = 255
    • Token type: 4 bits (b63~b60)
    • Reserved bit: 2 bits (b31: b30)

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