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| − | =VTD-XML Investigation=
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| − | VTD-XML ([http://vtd-xml.sourceforge.net/ http://vtd-xml.sourceforge.net/]) is a high-performance XML processing model that deals with XML in a binary form, instead of the traditional text form.
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| − | VTD-XML parses an XML document and builds an internal data structure representing the entire XML document in <tt>byte[]</tt> form. Each "token" of the XML document is represented as the following 64-bit integer:
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| − | [[Image:Vtd_layout.jpg]]
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| − | * It is a binary format specification, not an API specification
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| − | * 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:
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| − | ** Starting offset
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| − | ** Length
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| − | ** Nesting depth
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| − | ** Token type
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| − | * VTD requires that XML document be maintained intact in memory.
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| − | * Our current VTD record layout further specifies the following:
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| − | ** Use 64 bits as the primitive type (b63~b0)
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| − | ** Big endian
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| − | ** Starting offset: 30 bits (b29 ~ b0) maximum value is 2^30 -1 = 1G -1
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| − | ** Length: 20 bits (b51 ~ b32) maximum value is 2^20-1 = 1M -1
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| − | *** For some token type
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| − | **** Prefix length: 9 bits (b51~ b43) max value 511
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| − | **** Q-name length: 11 bits (b42 ~ b 32) max value 1023
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| − | ** Depth: 8 bits (b59~b52) max value is 2^8-1 = 255
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| − | ** Token type: 4 bits (b63~b60)
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| − | ** Reserved bit: 2 bits (b31: b30)
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| − | VTD stands for '''V'''irtual '''T'''oken '''D'''escriptor.
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| − | ==VTD-XML Core Concepts==
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| − | ===Unmarshalling a VTD-XML document===
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| − | <div style="width:900px">
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| − | <source lang="java">
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| − | VTDGen vg = new VTDGen();
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| − | // from existing byte[]
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| − | // true indicates namespace aware
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| − | vg.setDoc(byte[]); vg.parse(true);
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| − | // - or -
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| − | // from file
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| − | vg.parseFile("old.xml",false)
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| − | </source>
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| − | </div>
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