CS1655 Recitation 5

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CS1655 - Recitation 5

• Andreea Munteanu
• andreea_at_cs.pitt.edu

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Overview

• Introduction to XML
• DTD
• Example

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Why XML? HTML not enough?

• Need to do more fancy stuff
• Make the logical structure of documents more
  explicit
• eXtensible Markup Language
• Data are identified using tags (identifiers
  enclosed in angle brackets lt...gt)

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XML

• Collectively, the tags are known as markup
• XML tags tell you what the data means, rather
  than how to display it

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XML example

• lt?xml version"1.0" encoding"ISO-8859-1"?gt
• ltauthorsgt
• ltnamegt
• ltfirstnamegt Jon lt/firstnamegt
• lt/lastnamegt Patrick lt/lastnamegt
• lt/namegt
• ltnamegt
• ltfirstnamegt Andrew lt/firstnamegt
• lt/lastnamegt Moore lt/lastnamegt
• lt/namegt
• lt/authorsgt

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XML versus relational

• Relational structured
• XML semi-structured
• Plain text file unstructured

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How does XML work?

• XML allows developers to write their own Document
  Type Definitions
• DTD markup languages rule book
• Why need DTD?
• Common format for XML documents
• Consequence
• If you want to use a certain tag must be defined
  in the DTD

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Key concepts in XML
XML Content
XML Parser
Application
DTD Rules
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DTD example

• lt!ELEMENT authors (name)gt
• lt!ELEMENT name (firstname, lastname)gt
• lt!ELEMENT firstname (PCDATA)gt
• lt!ELEMENT lastname (PCDATA)gt

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XML and DTD

• lt?xml version"1.0" encoding"ISO-8859-1"?gt
• lt!DOCTYPE authors SYSTEM authors.dtdgt
• ltauthorsgt
• ltnamegt
• ltfirstnamegt Jon lt/firstnamegt
• lt/lastnamegt Patrick lt/lastnamegt
• lt/namegt
• ltnamegt
• ltfirstnamegt Andrew lt/firstnamegt
• lt/lastnamegt Moore lt/lastnamegt
• lt/namegt
• lt/authorsgt

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XML and DTD

• lt?xml version"1.0" encoding"ISO-8859-1"?gt
• ltDOCTYPE authors
• lt!ELEMENT authors (name)gt
• lt!ELEMENT name (firstname, lastname)gt
• lt!ELEMENT firstname (PCDATA)gt
• lt!ELEMENT lastname (PCDATA)gt
• gt
• ltauthorsgt
• ltnamegt
• ltfirstnamegt Jon lt/firstnamegt
• lt/lastnamegt Patrick lt/lastnamegt
• lt/namegt
• lt/authorsgt

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Elements

• Everything from (including )the elements start
  tag to (including) the elements end tag
• Content
• Elements
• ltnamegt ltfirstnamegtJonlt/firstnamegtlt/namegt
• Simple or text
• ltfirstnamegt Jon lt/firstnamegt

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Elements

• Content (continue)
• Mixed
• ltchaptergt XML tutorial
• ltparagt Introduction to XMLlt/paragt
• ltparagt Description lt/paragt
• lt/chaptergt
• Empty (no information)
• ltproduct id111 typebookgtlt/productgt
• Attributes
• Id with value 111 and type with value
  book

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Attributes

• Elements can have attributes in the start tag
• Attributes values must always be enclosed in
  simple or double quotes
• ltchapter date03/18/05gt
• lttitlegt Introduction to XML lt/titlegt
• ltcontentgt lt/contentgt
• lt/chaptergt

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Attributes

• Not used very much
• Cannot contain multiple values
• Cannot describe structures
• More difficult to implement by program code
• Attributes values are not easy to test against
  DTD

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DTD

• XML documents may contain
• Elements
• Tags
• Attributes
• PCDATA (Parsed Character Data)
• CDATA (Character Data)
• This one will NOT be parsed by a parser. Tags
  inside the text will not be treated as markup and
  entities will not be expanded.

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DTD

• XML documents may contain
• Entities
• Variables used to define common text.
• lt means lt
• gt means gt
• amp means
• quot means

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DTD Elements

• lt! ELEMENT element-name categorygt
• lt! ELEMENT element-name (element-content)gt
• lt! ELEMENT element-name EMPTYgt
• lt! ELEMENT element-name (PCDATA)gt
• lt! ELEMENT element-name (ANY)gt
• lt! ELEMENT element-name (child-element-name,
  child-element-name, )gt

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DTD Elements

• lt! ELEMENT element-name (child-element-name)gt
• Appear at least once.
• lt! ELEMENT element-name (child-element-name)gt
• Appear zero or more times.
• lt! ELEMENT element-name (child-element-name?)gt
• Appear zero or one time.
• lt! ELEMENT element-name (child-element-name1
  child-element-name2)gt
• One of the two appears.

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DTD Attributes

• ltATTLIST element-name attribute-name
  attribute-type default-valuegt
• lt!ATTLIST payment type CDATA checkgt
• XML ltpayment typecheck/gt

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DTD Attribute Type

• CDATA
• Value is character data.
• (en1en2..)
• Value must be one of the enumerated list.
• ID
• Values is a unique ID.
• IDREF
• Value is ID of another element.
• NMTOKEN
• Value is a valid XML name.