LASXML, Validation, and RELAX NG

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LAS-XML, Validation, and RELAX NG

• Jon Callahan(standing in for Roland Schweitzer)

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LAS use of XML

• LAS (will) store all configuration information
  in XML documents
• Server configuration
• User Interface components
• Dataset descriptions
• Variables
• User Interface presentation
• Product generation hints
• Data access hints

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LAS use of XML
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Sister servers

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Improving our use of XML

• GOALS
• Have all configuration information in XML
• Be able to create a schema for validation
• Better separate UI vs. product server info
• Expanded set of information
• Clean up inconsistencies

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New dataset XML

• ltlasdata version"6.5"gt
• ltdataset
• doc"http//www.cdc.noaa.gov/cdc/data.coad
  s.ltm.html"
• ID"CDC014"
• name"COADS LTMs"gt
• ltvariable
• ID"V2"
• name"Sea Surface Temperature"
• units"degC"
• url"file//Datasets/coads_2d_g_std/ss
  t.mean.ncsst"gt
• ltgrid IDREF"G88"/gt
• lt/variablegt
• ltvariablegt lt/variablegt
• lt/datasetgt

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New dataset XML

• ltgrid ID"G88"gt
• ltaxis IDREF"CDC014-lon17"/gt
• ltaxis IDREF"CDC014-lat18"/gt
• ltaxis ID"CDC014-time88" type"t"
  units"month"gt
• ltarange size"120" start"1990-01-01"
  step"1"/gt
• lt/axisgt
• lt/gridgt
• ltaxis ID"CDC014-lon17" type"x"
  units"degrees_east"gt
• ltarange size"180" start"1" step"2"/gt
• lt/axisgt
• ltaxis ID"CDC014-lat18" type"y"
  units"degrees_north"gt
• ltarange size"90" start"-89" step"2"/gt
• lt/axisgt
• lt/lasdatagt

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Well formed vs. valid

• 10 of XML documents have errors!
• Well formed means that the XML syntax is
  correct.
• Valid means that the XML conforms to a schema
  (or DTD).
• Tools are available to validate XML against your
  schema.
• Automatic validation means less user support!

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Writing schemas with RELAX NG

• RELAX NG is a newly popular tool for writing XML
  schemas.
• RELAX NG focuses on XML tree structure(not
  element content).
• RELAX NG schemas are easy to write.
• RELAX NG schemas are easy to read.
• Working with RELAX NG is fun! (Roland)

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RELAX NG schema for ltlasdatagt

• ltdefine name"Lasdata"gt
• ltelement name"lasdata"gt
• ltattribute name"version"/gt
• ltinterleavegt
• ltoneOrMoregt
• ltref name"Dataset"/gt
• lt/oneOrMoregt
• ltoneOrMoregt
• ltref name"Grid"/gt
• lt/oneOrMoregt
• ltoneOrMoregt
• ltref name"Axis"/gt
• lt/oneOrMoregt
• lt/interleavegt
• lt/elementgt
• lt/definegt

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Useful links

• The RELAX NG Tutorial at Oasis.
• A 3-part series of "XML Matters" columns entitled
  "Kicking back with RELAX NG" by David Mertz (Part
  1, Part 2, and Part 3).
• An article about the design philosophy behind
  RELAX NG.
• The text of a book on RELAX NG to be published by
  O'Reilly Associates.
• A C-library that includes RELAX NG validation
  with Perl bindings via XML-LibXML.