Validation of a CGM Graphic Against the Web CGM Profile

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Validation of a CGM Graphic Against the Web CGM
Profile

• Stuart Galt
• The Boeing Company

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Agenda

• What is the WebCGM profile
• The process
• Hard parts

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WebCGM

• CGM (ISO 8632) vector and composite vector/raster
  graphic format.
• WebCGM is a profile used to specify the subset of
  the CGM standard that will be used to exchange
  data on the web.

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WebCGM History

• 1987 - ISO approved CGM as a Standard
• 1995 - CGM became a registered mime type
• 1996 - W3C published Scalable Graphics
  Requirements
• 1997 - W3C published Use of CGM as a Scalable
  Graphic Format
• 1999 - WebCGM 1.0 approved in January

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WebCGM is intelligent

• Contains graphic primitives
• Lines, polylines, polygons
• Rectangles, circles, ellipses, arcs
• Graphical text
• Non graphical content
• Metadata
• Hierarchies objects
• Links

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The Process
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CGM to XML

• CGM graphic primitives are converted directly
• Containers are used to represent internal state
  changes

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CGM primitives

• Circle centered (4252, 2385) radius 150
• Binary CGM
• 41 86 10 9c 09 51 00 96
• XML
• ltCirclegtltPoint x4252 y2385/gtltRadius
  r150/gtlt/Circlegt

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CGM primitives (contd)

• Restricted Text
• ltRestrictedText final"yes"gtltDeltaBox dx"400"
  dy"97"/gtltPoint x"914" y"1953"/gtltStringFixedgtN
  OTElt/StringFixedgtlt/RestrictedTextgt

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CGM primitives (contd)

• Polygon
• ltPolygongtltPoint x"3175" y"3879"/gtltPoint
  x"3085" y"3833"/gtltPoint x"3075"
  y"3866"/gtlt/Polygongt

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CGM States

• Container elements used to mark state changes
• Metafile defaults
• ltMetafileDefaultsReplacementgt defaults go here
  lt/MetafileDefaultsReplacementgt

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CGM States (contd)

• Picture Descriptor and Picture Open State
• ltPicturegtltStringFixedgtPicture
  Descriptionlt/StringFixedgt
• Picture descriptor data here
• ltBeginPictureBody/gtPicture data
  herelt/Picturegt

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CGM
States
Metafile Descriptor
Picture
Picture
Picture Descriptor
Picture Body
EndPic
Picture Body
Picture Open
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Metafile Decsriptor
Metafile
Descriptor
opt rep
MFVersion
IntegerPrec
MFDesc
VDCType
RealPrec
IndexPrec
ColrIndexPrec
MaxColrIndex
ColrValueExt
MFElemlist
ColrPrec
CharSetList
CharCoding
NamePrec
MaxVDCExt
FontList
SetPriExt
ColrModel
GlyphMap
SymLibList
ColrCalib
FontProp
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Validating WebCGM

• Current state
• Profile validation tool exists for WebCGM in
  binary encoding
• Metacheck
• With a WebCGM schema defined
• General purpose tools would be available

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The Schema

• Some elements are easy to represent
• Some are hard

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Metafile Version

• ltelement name"MetafileDescriptor"gt
• ltcomplexTypegt
• ltsequencegt
• ltelement name"MetafileVersion"gt
• ltattribute nameversion userequired
• typeinteger minInclusive1
• maxInclusive4/gt
• lt/elementgt
• ltallgt
• ltelement name"MetafileDescription"
  type"string"/gt
• ...other required elements go here...
• lt/allgtlt/sequencegtlt/complexTypegtlt/elementgt

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Non Graphical Text String

• ltsimpleType nameNonGraphicTextgt
• ltrestriction basestringgt
• ltminlength value0/gt
• ltmaxlength value254/gt
• lt/restrictiongt
• lt/simpleTypegt

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The Hard

• Some elements are restricted (or required based
  on the value of the metafile version
• If version 3 then a RestrictedTextType
  element must appear before the first
  RestrictedText element
• If ColorSelectionMode is indexed color is index
  value, else color is RGB values

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The Hard Part

• Branching logic
• If (condition a) then foo else bar

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Conclusion

• Creation of a schema that enforces WebCGM profile
  allows simple XML schema validator to validate
  conformance of CGM graphics.
• This approach could also be used to simplify
  validation of other binary structured formats.

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Whats Ahead

• Complete mapping CGM binary to XML
• Finish WebCGM schema
• Work to continue in CGM Open Consortium
  http//www.cgmopen.org