XML Syntax Writing XML and Designing DTD's

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XML Syntax - Writing XML and Designing DTD's
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HTML 1st Example

• lthtmlgtltheadgtlttitlegtChocolate Cakelt/titlegtltbodygt
• ltbgtIngredient Listlt/bgtlthr /gt
• ltbrgt2 cups flour
• ltbrgt1 cup sugar
• ltbrgt2 bars chocolate
• ltbrgt1 cup milk
• ltbrgtltbrgtltbgtInstructionslt/bgt
• lthrgtltbrgtMix flour, sugar and milk
• ltbrgtEat chocolate
• ltbrgtBake at 400 degrees
• lt/bodygtlt/htmlgt

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XML Document Structure

• Text file containing Elements, Attributes Text
• lt?xml version1.0 ?gt
• ltRecipe nameChocolate Cake typeDesert gt
• ltIngredientListgt
• ltIngredientgt2 cups flourlt/Ingredientgt
• ltIngredientgt1 cup sugarlt/Ingredientgt
• lt/IngredientListgt
• ltInstructiongtSift the flourlt/Instructiongt
• lt/Recipegt

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XML Document Structure

• Text file containing Elements, Attributes Text
• lt?xml version1.0 ?gt
• ltRecipe nameChocolate Cake typeDesert gt
• ltIngredientListgt
• ltIngredientgt2 cups flourlt/Ingredientgt
• ltIngredientgt1 cup sugarlt/Ingredientgt
• lt/IngredientListgt
• ltInstructiongtSift the flourlt/Instructiongt
• lt/Recipegt

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10 Rules Well Formed XML1. Must start with XML
declaration

• lt?xml version1.0 ?gt

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2. Must be only one document element

• Valid Example(s)
• lt?xml version1.0 ?gt
• ltrecipegt
• lt/recipegt
• or
• ltrecipeBookgt
• ltrecipegtlt/recipegt
• ltrecipegtlt/recipegt
• lt/recipeBookgt

• Invalid Example
• lt?xml version1.0?gt
• ltrecipegt
• lt/recipegt
• ltrecipegt
• lt/recipegt

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3. Match opening closing tags

• Carry over from html origins
• lthrgt ltpgt or ltboldgtltitalicgtlt/boldgtlt/italicgt
• Browsers forgive, XML Parsers do NOT
• ltpgtlt/pgt or ltbr /gt
• ltboldgtltitalicgtlt/italicgtlt/boldgt
• ltrecipegtlt/recipegt

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4. Comments allowed, but not inside attribute or
element tag

• lt!-- Isnt XML really cool? --gt
• lt!-- Just like being a student!!! --gt

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5. Elements and Attributes must start with a
letter

• ltRecipegt OK
• ltSecond thirdfalsegt OK
• lt2ndgt INVALID
• ltRecipe 2ndtruegt INVALID

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6. Attributes must go in the opening tag

• Valid
• ltrecipe nameChocolate Cake
• categoryDesertgtlt/recipegt
• Invalid
• ltrecipegtlt/recipe nameChocolate Cakegt

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7. Attributes must be enclosed in matching quotes

• Can use either single or double quotes but must
  use same type to start and end attribute value
• NameAustralian Computer Society
• NameAustralian Computer Society

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Lets finish these rules!

• 8. Only simple text for attributes, no nested
  values. Nesting is allowed in elements, not in
  attributes.
• 9. Use lt amp gt quot and apos for
  special characters. lt gt
• 10. Write empty elements using ltrecipe /gt syntax
  if no nested values, can still have attributes in
  tag ltrecipe typedesert /gt.

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With these 10 rules, we have a Well Formed xml
document

• It means the xml can be read, processed or
  parsed.
• Doesnt mean the structure makes sense.
• ltrecipe modelHoldengt
• ltchaptergtlt/chaptergt
• ltengine cylinders4gtlt/enginegt
• ltrecipegt

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Examples

• Buggy dictionary
• Non-buggy dictionary
• FIDA

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DTD Document Type Definition

• Allows us to define the exact elements and
  attributes for the document
• These effectively become the rules of our own
  markup language, the extensible part of xml
• DTD really only defines the structure, limited
  in what you can validate in regards to the text
  values of the element or attribute.

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Recipe DTD

• lt!ELEMENT Recipe (Name, Description?,
  Ingredients?, Instructions?)gt
• lt!ELEMENT Name (PCDATA)gt
• lt!ELEMENT Ingredient (Qty, Item)gt
• lt!ELEMENT Qty (PCDATA)gt
• lt!ATTLIST Qty unit CDATA REQUIREDgt
• lt!ELEMENT Item (PCDATA)gt
• lt!ATTLIST Item optional CDATA 0 isVegetarian
  CDATA truegt

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Elements

• Basic rules
• Start tag lttag_namegt and end tag lt/tag_namegt
• Tags must be nested
• lttag1gtlttag2gtlt/tag2gtlt/tag1gt
• Tags may be empty (no enclosed data)
• ltempty_tag/gt
• Whitespace in element content usually ignored
• ltsectiongtltpgt lt/pgtlt/sectiongt
• ltsectiongt ltpgt lt/pgtlt/sectiongt

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Element Declarations

• Used to define new elements and their content
• lt!ELEMENT name (PCDATA)gt ? ltnamegt lt/namegt
• Empty element has no content
• lt!ELEMENT name EMPTYgt ? ltname/gt
• When children allowed - any or model group
• lt!ELEMENT name ANYgt
• lt!ELEMENT person (name, e-mail)gt

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Model Groups

• Used to define content of elements
• lt!ELEMENT person (name, e-mail)gt
• Used to define hierarchies of elements
• lt!ELEMENT name (fname, surname)gt lt!ELEMENT
  fname (PCDATA)gtlt!ELEMENT surname
  (PCDATA)gtlt!ELEMENT e-mail (PCDATA)gt
• Control organisation of elements
• Sequence connector - ',' - (A, B, C) then
• Choice connector - '' - (A B C) or

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Model Group Quantity Indicators

• Describe constraints on elements in DTD A? May
  occur 0..1 A Must occur 1.. A May
  occur 0.. A B Either A or B A, B A
  followed by B (A, B) ((A,B?) C)

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Attributes

• Provide additional information about an element
• Enclosed by quotes - either " or '
• Case-sensitive
• May be character data or tokenized
• value"Blue Peter" (character data)
• value "blue" (single token)
• value "red green blue" (tokens)
• Values may be enumerated or defaulted (DTD)

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Attribute Declarations

• Attributes can be attached to elements
• Declared separately in ATTLIST declaration
• lt!ATTLIST tag gt
• Rest of definition specifies
• attribute name
• attribute type
• default value

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Attribute Names and Types

• Attribute name
• lt!ATTLIST tag nme type defaultgt
• lt!ATTLIST tag first_attr
  secon_attr third_attr gt
• Attribute types

CDATA NMTOKEN NMTOKENS ENTITY ENTITIES
ID IDREF IDREFS NOTATION name group
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Attribute Types

• CDATA
• Character data
• NMTOKEN
• Single token
• NMTOKENS
• Multiple tokens
• ENTITY
• Attribute is entity ref
• ENTITIES
• Multiple entity ref's

• ID
• Unique ID
• IDREF
• Match to ID
• IDREFS
• Match to multiple ID's
• NOTATION
• Describe non-XML data
• Name group
• Restricted list

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Attribute Types

• CDATA
• lt!ATTLIST person name CDATA gt
• NMTOKEN
• lt!ATTLIST mug color NMTOKEN gt
• NMTOKENS
• lt!ATTLIST temp values NMTOKENS gt
• ENTITY
• lt!ATTLIST person photo ENTITY gt
• ENTITIES
• lt!ATTLIST album photos ENTITIES gt

• ID
• lt!ATTLIST person id ID gt
• IDREF
• lt!ATTLIST person father IDREF gt
• IDREFS
• lt!ATTLIST person children IDREFS gt
• NOTATION
• lt!ATTLIST image format NOTATION (TeXTIFF) gt
• Name group
• lt!ATTLIST point coord (XYZ) gt

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Attribute Types

• CDATA
• name "Tom Jones"
• NMTOKEN
• color"red"
• NMTOKENS
• values"12 15 34"
• ENTITY
• photo"MyPic"
• ENTITIES
• photos"pic1 pic2"

• ID
• ID "P09567"
• IDREF
• IDREF"P09567"
• IDREFS
• IDREFS"A01 A02"
• NOTATION
• FORMAT"TeX"
• Name group
• coord"X"

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Default Attribute Values

• Can specify a default attribute value for when
  its missing from XML document, or state that
  value must be entered
• REQUIRED Must be specified
• IMPLIED May be specifed
• "default" Default value if unspecified
• FIXED Only one value allowed

ltATTLIST tag name type
defaultgt lt!ATTLIST seqlist sepchar NMTOKEN
REQUIRED type (alphanum)
"num"
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Declarations

• Instructions for the XML processor
• Format - lt! gt or lt! lt! gtgt
• Document type - lt!DOCTYPE gt
• Character data - lt!CDATA gt
• Entities - lt!ENTITY gt
• Notation - lt!NOTATION gt
• Element - lt!ELEMENT gt
• Attributes - lt!ATTLIST gt
• lt!INCLUDEgt and lt!IGNOREgt

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Document Type Declaration

• Identifies the name of the document root element
• lt!DOCTYPE My_XML_Docgt
• May also add entity definitions and DTD
• lt!DOCTYPE My_XML_Doc gtltMy_XML_Docgt
  ...lt/My_XML_Docgt

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Comment Declaration

• Comments are not considered part of XML document
  and should not be published
• lt!-- A comment --gt
• Cannot have additional '--' in comment
• Cannot embed inside other declarations

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Character Data Declaration

• For occasions when text must contain
  uninterpreted markup characters
• Press ltltltENTERgtgtgt
• lt!CDATAPress ltltltENTERgtgtgtgt

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Processing Instructions

• Information required by an external application
• Processing Instructions
• Format - lt? ?gt
• XML PI - lt?xml version'1.0 ?gt
• Confusingly, this is called the XML declaration,
  but is a processing instruction

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Entities

• XML document may be distributed among a number of
  files
• Each unit of information is called an entity
• Each entity has a name to identify it
• Defined using an entity declaration
• Used by calling an entity reference

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When to use Entities

• Use an entity when the information
• Is used in several places
• May be represented differently
• Is part of a larger document that needs to be
  split up to be manageable
• Conforms to a data format other than XML

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Types of Entity

• General Entity
• Referred to in XML document
• Parameter Entity
• Referred to in markup declarations in DTD

• Internal Entity
• Stored in main document
• Text content only
• External Entity
• Stored externally to the main document
• Text or binary
• Can use to group many internal entities together

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General Entities

• Declared in 'Document Type Declaration'
• lt!DOCTYPE My_XML_Doc lt!ENTITY name
  "replacement"gt gt
• lt!ENTITY xml "eXtensible Markup Language"gt
• The xml includes entities
• The eXtensible Markup Language includes entities

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Parameter Entities

• Declared in 'Document Type Declaration'
• lt!DOCTYPE My_XML_Doc lt!ENTITY name
  "replacement"gt gt
• lt!ENTITY param "(para list)"gt
• lt!ELEMENT section (param)gt

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External Entities

• External Text Entities
• Location specified with SYSTEM keyword
• lt!ENTITY ent SYSTEM "/ENTS/MYENT.XML"gt
• May specify with public identifier
• lt!ENTITY ent PUBLIC "-//EBI//ENTITIES ents//EN"
  gt
• External Binary Entities
• Need to identify format of data - NDATA
• lt!ELEMENT pic EMPTYgtlt!ATTLIST pic name ENTITY
  REQUIREDgtlt!ENTITY photo SYSTEM
  "/ENTS/photo.tif" NDATA TIFFgt
• Referenced by empty element
• A photograph ltpic name"photo"/gt.

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Restrictions on Entities

• General text entities
• Can appear in element content
• ltparagt ent lt/paragt
• Can appear in attribute value
• ltpara name"ent"gt lt/paragt
• Can appear in internal entity content
• lt!ENTITY cod "ent"gt
• Cannot appear in other parts of DTD

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Restrictions on Entities (2)

• Binary entities
• If entity content is not XML, the entity cannot
  be used as a textual reference
• Error - lt!ELEMENT sec (paraphoto)gt
• Error - ltparagt photo lt/paragt
• Binary entity can only appear as an attribute of
  type ENTITY
• lt!ENTITY photo SYSTEM "photo.tif" NDATA
  TIFFgtlt!ELEMENT pic (PCDATA)gtlt!ATTLIST pic
  name ENTITY REQUIREDgt

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Parameter Entities

• Use parameter entities within DTD
• lt!ENTITY common "(paralisttable)"gtlt!ELEMENT
  chapter ((common), section)gtlt!ELEMENT
  section (common)gt
• Safest to include parentheses in entity
  definition and around entity reference

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Putting it all together...

• Have now been introduced to the main components
  and rules of XML and DTDs
• Entities, elements, declarations, processing
  instructions, attribute lists
• Use all these components in the 'Document
  Definition Type' (DTD) to specify the rules about
  the format of the XML document