XML Schema

1
XML Schema

• Neal Arthorne
• 12/12/2001

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Extensible Markup Language (XML)

• Format for holding structured data
• Specification was recommended by the World Wide
  Web Consortium (W3C) on
• 6 October 2000
• Widely accepted as a universal data format
• Can be manipulated and transformed into other
  languages

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XML Document
ltbook conditionmintgt lttitlegtThe Soul of a
New Machinelt/titlegt ltauthorgtTracy
Kidderlt/authorgt ltdategt1981lt/dategt
ltpublishergtAtlantic-Little, Brownlt/publishergt
ltisbngt0-316-49170-5lt/isbngt lt/bookgt
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XML Structure

• What elements go where?
• XML Validation
• Shared understanding of XML structure facilitates
  exchange of XML data

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XML Data Types

• What values are allowed for attributes?
• What is the type of data in an element or
  attribute?
• In XML, data is written as text, but what if we
  want it to be interpreted as integers, strings or
  floating point numbers?

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Solution XML Schema

• XML Schema is a markup language used to describe
  the structure and data types of an XML document
• W3C Recommendation 2 May 2001
• Many advantages over older DTDs re-usable
  definitions, written in XML, data types,
  documentation support

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XML Schema

• Elements and Attributes are defined using Simple
  and Complex Types
• SimpleType
• No nested child elements or attributes
• Fixed set of acceptable values
• Derived from built-in SimpleTypes or user-defined
  SimpleTypes

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Built-In SimpleTypes

• String
• Decimal
• Float
• Integer
• Time
• Date
• Token

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XML Schema ComplexTypes

• Nested elements and attributes
• Derived by extending Simple or Complex Types
• Highest level of sophistication
• Uses sequence or choice

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XML Schema

• ltschemagt
• ltelement namebook/gt
• ltcomplexTypegt
• ltsequencegt
• ltelement nametitle typestring/gt
• ltelement nameauthor typestring/gt
• lt/sequencegt
• ltattribute namecondition
  typeConditionType/gt
• lt/complexTypegt
• lt/elementgt
• lt/schemagt

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SimpleType

• ltattribute namecondition typeConditionType/gt
  
• Need to define a fixed set of values for the
  condition of a book
• conditionmint
• conditionvery good
• conditiongood
• conditionfair
• conditionpoor
• Enumeration

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SimpleType

• Derive from the built-in string type
• ltsimpleType name"ConditionType"gt
• ltrestriction base"string"gt
• ltenumeration value"mint" /gt
• ltenumeration value"very good" /gt
• ltenumeration value"good" /gt
• ltenumeration value"fair" /gt
• ltenumeration value"poor" /gt
• lt/restrictiongt
• lt/simpleTypegt

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SimpleType

• Derived from a base type built-in or already
  defined
• Defines all the values an attribute or element
  can have (data type)
• Can be derived by three methods
• Union Combine all values from other SimpleTypes
• List A list of items where each item is of the
  same SimpleType
• Atomic Restrict the values of a SimpleType using
  constraints

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SimpleType Union

• ltsimpleType nameDateAndInt"gt
• ltunion memberTypes"date integer" /gt
• lt/simpleTypegt
• Valid values 2001-12-12, -34, 23, 1900-01-20
• Combines all values in date type with all
  values in integer type

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SimpleType List

• ltsimpleType name"MyIntegerList"gt
•   ltlist itemType"integer" /gt
• lt/simpleTypegt
• Valid Values -10 30 23 -100, 0 1 2 3 4 5
• List items are separated by whitespace
• Every item in this list is of type integer
• Length of the list is unlimited

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SimpleType Atomic

• Imposes a restriction on an existing type
• The base type determines what constraints can be
  used
• String maxLength, minLength, length,
  enumeration, pattern
• Integer minInclusive, maxInclusive, totalDigits,
  fractionDigits, enumeration

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My Project SchemaTool

• Web-based XML Schema editor
• Designed for the novice user
• Limited subset of XML Schema
• Allows creation of simpleTypes
• Use single level schema structure to describe a
  Resource

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SchemaTool Context

• Designed to integrate into U-P2P
• Used by a user to describe a Resource
• Resource book
• Property A title
• Property B author
• Property C publisher

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SchemaTool Usage

• XML Schema used to describe a single level
  hierarchy
• ltbook conditionmintgt
• lttitlegtlt/titlegt
• ltauthorgtlt/authorgt
• lt/bookgt
• No nested elements (inside of title, author) and
  no attributes

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SchemaTool

• Requires no knowledge of XML or XML Schema
• Provides a wizard interface for creating new
  simpleTypes
• Download the schema when completed to an XML file
• Not a complete XML Schema implementation