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XSD: XML Schema Language

XSD: XML Schema Language. Kanda Runapongsa ( krunapon@kku.ac.th ) Dept. of Computer Engineering Khon Kaen University. XML Schema & DTD. Like a DTD, its purpose is to define the legal building blocks of an XML document defines elements that can appear in a document

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XSD: XML Schema Language

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  1. XSD: XML Schema Language Kanda Runapongsa (krunapon@kku.ac.th) Dept. of Computer Engineering Khon Kaen University

  2. XML Schema & DTD • Like a DTD, its purpose is to define the legal building blocks of an XML document • defines elements that can appear in a document • defines attributes that can appear in a document • defines which elements are child elements 168493: XML and Web Services (II/2546)

  3. XML Schema & DTD (Cont.) • defines the order of child elements • defines the number of child elements • defines whether an element is empty or can include text • defines data types for elements and attributes • defines default and fixed values for elements and attributes 168493: XML and Web Services (II/2546)

  4. Advantages of XSD over DTD • XML Schemas use XML syntax • Do not need to learn a new syntax • Use any XML parser to parse XML schemas • XML Schemas support many data types and allow you to create new data types • No ‘Integer’ or ‘Double’ types in DTD 168493: XML and Web Services (II/2546)

  5. Adv. of XSD over DTD (Cont.) • XML Schemas allow you to group elements to control the recurrence of elements and attributes • In DTD, we cannot specify that the number of occurrences of elements must be at least 2 and at most 5 • XML Schemas support namespaces 168493: XML and Web Services (II/2546)

  6. The <schema> Element • The <schema> element is the root element of every XML Schema: <?xml version="1.0"?> <xs:schema> ... ... </xs:schema> 168493: XML and Web Services (II/2546)

  7. The <schema> Element (Cont.) <?xml version="1.0"?> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://abc.com" xmlns=“http://abc.com" elementFormDefault="qualified"> ... ... </xs:schema> 168493: XML and Web Services (II/2546)

  8. Attributes of <Schema> xmlns:xs=“http://www.w3.org/2001/XMLSchema” • Indicates that the elements and data types used in the schema (schema, element,…) come from the http://www.w3.org/2001/XMLSchema namespace • These elements and data types should be prefixed with xs: 168493: XML and Web Services (II/2546)

  9. Attributes of <Schema> (Cont.) targetNamespace=“http://abc.com” • Indicates that the elements defined by this schema (Note, To, From,..) is in the "http://www.w3schools.com" namespace 168493: XML and Web Services (II/2546)

  10. Attributes of <Schema> (Cont.) xmlns=“http://abc.com” • Indicates that the default namespace is http://abc.com elementFormDefault="qualified“ • indicates that any elements used by the XML instance document which were declared in this schema must be namespace qualified. 168493: XML and Web Services (II/2546)

  11. XSD Simple Elements • A simple element • Can contain only text • Cannot contain any other elements • Cannot contain any attributes • Can text be any other types besides string? • It can be date, etc., or even a custom type that you can define yourself 168493: XML and Web Services (II/2546)

  12. Defining a Simple Element • The syntax for defining a simple element is: <xs:element name="xxx" type="yyy"/> • where xxx is the name of the element and yyy is the data type of the element. 168493: XML and Web Services (II/2546)

  13. Simple Elements: Example • Some XML elements • <lastname>Wasee</lastname> • <age>34</age> • Corresponding element definitions • <xs:element name=“lastname” type=“xs:string”/> • <xs:element name=“age” type=“xs:integer”/> 168493: XML and Web Services (II/2546)

  14. Built-in Data Types • xs:string • xs:decimal • xs:integer • xs:boolean • xs:date • xs:time 168493: XML and Web Services (II/2546)

  15. Simple Elements: Default Values • Simple elements can have a default value • A default value is automatically assigned to the element when no value is specified <xs:element name=“To” type=“xs:string” default=“students”/> 168493: XML and Web Services (II/2546)

  16. Simple Elements: Fixed Values • A fixed value is automatically assigned to elements • We cannot specify another value <xs:element name=“To” type=“xs:string” fixed=“students”/> 168493: XML and Web Services (II/2546)

  17. XSD Attributes • All attributes are declared as simple types • Only complex elements can have attributes • An element with attributes always has a complex type definition 168493: XML and Web Services (II/2546)

  18. Defining an Attribute • Syntax: <xs:attribute name=“xxx” type=“yyy”/> Where xxx is the name of the attribute and yyy is the data type of the attribute • Examples: XML:<lname lang=“EN”>Dee</name> XSD:<xs:attribute name=“lang” type=“xs:string”/> 168493: XML and Web Services (II/2546)

  19. Default & Fixed Values for Attributes • Attributes can have a default value or a fixed value specified • Examples: • <xs:attribute name=“lang” type=“xs:string” default=“EN”/> • <xs:attribute name=“lang” type=“xs:string” fixed=“EN”/> 168493: XML and Web Services (II/2546)

  20. Optional & Required Attributes • All attributes are optional by default • To explicitly specify that the attribute is optional or required, use the “use” attribute • Examples: • <xs:attribute name=“lang” type=“xs:string” use=“optional”/> • <xs:attribute name=“lang” type=“xs:string” use=“required”/> 168493: XML and Web Services (II/2546)

  21. Restrictions on Content • When an XML element or attribute has a type defined, it puts a restriction for the element’s or attribute’s content • We can also add our own restrictions to our XML elements and attributes • These restrictions are called facets 168493: XML and Web Services (II/2546)

  22. XSD Restrictions/Facets • Restrictions are used to control acceptable values for XML elements or attributes • Many kinds of restrictions/facets • Restrictions on values • Restrictions on white spaces • Restrictions on length 168493: XML and Web Services (II/2546)

  23. Restrictions on Values • This example defines an element called “age” with a restriction. <xs:element name=“age”> <xs:simpleType> <xs:restriction base=“xs:integer”> <xs:minInclusive value=“0”/> <xs:maxInclusive value=“60”/> … </xs:element> • What range the value of age is in? • Cannot be lower than 0 or greater than 60 168493: XML and Web Services (II/2546)

  24. Restriction on a Set of Values • To limit the content of an XML element to a set of acceptable values, we would use the enumeration constraint <xs:element name=“grade”> <xs:simpleType> <xs:restriction base=“xs:string”> <xs:enumeration value=“A”/> <xs:enumeration value=“B”/> … </xs:element> 168493: XML and Web Services (II/2546)

  25. Restrictions on a Series of Values • To limit the content to a series of numbers or letters, use the pattern constraint <xs:element name=“letter”> <xs:simpleType> <xs:restriction base=“xs:string”> <xs:pattern value=“[a-z]”/> … </xs:element> • What are the acceptable values of the “letter” element? 168493: XML and Web Services (II/2546)

  26. Restrictions on a Series of Values <xs:element name="letter"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:pattern value="([a-z][A-Z])+"/> … </xs:element> • What are the acceptable values of the “letter” element? 168493: XML and Web Services (II/2546)

  27. Restrictions on a Series of Values <xs:element name="password“> <xs:simpleType> <xs:restriction base="xs:string"> <xs:pattern value="[a-zA-Z0-9]{8}"/> … <xs:element> • What are the acceptable values of the “password” element? 168493: XML and Web Services (II/2546)

  28. Restrictions on White Space Characters • To specify how white space characters should be handled, use the whiteSpace constraint <xs:element name="address"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:whiteSpace value="preserve"/> … </xs:element • The XML processor will not remove any white space characters 168493: XML and Web Services (II/2546)

  29. Restrictions on White Space Characters • Three values of whiteSpace • preserve: the XML processor will not remove any white space characters • replace: the XML processor will replace all white space characters with spaces • collapse: the XML processor will remove all white space characters (leading and trailing spaces are removed) 168493: XML and Web Services (II/2546)

  30. Restrictions on Length <xs:element name="password"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:length value="8"/> … </xs:element> • Can we specify the minimum and maximum length of the value? • Yes, use “minLength” and “maxLength” 168493: XML and Web Services (II/2546)

  31. What is a Complex Element? • A complex element is an XML element that contains other elements and/or attributes • Four kinds of complex elements • Empty elements • Elements that contain only other elements • Elements that contain only text • Elements that contain both other elements and text 168493: XML and Web Services (II/2546)

  32. Complex Elements • Ex1: <product pid=“1345”/> • Ex2: <a><b>1</b><c>2</c></a> • Ex3: <food type=“dessert”>Ice cream</food> • Ex4: <description>Today is <date>11.13.2003</date></description> 168493: XML and Web Services (II/2546)

  33. Defining a Complex Element <xs:element name=“employee”> <xs:complexType> <xs:sequence> <xs:element name=“firstname” type=“xs:string”/> <xs:element name=“lastname” type=“xs:string”/> … </xs:element> 168493: XML and Web Services (II/2546)

  34. Sharing the Element Type <xs:element name=“employee” type=“personinfo”/> <xs:element name=“student” type=“personinfo”/> <xs:complexType name=“personinfo”> <xs:sequence> <xs:element name=“firstname” … </xs:element> 168493: XML and Web Services (II/2546)

  35. Defining Based on Other Types <xs:element name="employee" type="fullpersoninfo"/> <xs:complexType name="personinfo"> … </xs:complexType> <xs:complexType name="fullpersoninfo"> <xs:complexContent> <xs:extension base="personinfo"> <xs:sequence> <xs:element name="address" type="xs:string"/> … </xs:complexType> 168493: XML and Web Services (II/2546)

  36. Types for Empty Elements • XML: <product prodid="1345" /> • XSD: <xs:element name="product" type="prodtype"/> <xs:complexType name="prodtype"> <xs:attribute name="prodid" type="xs:positiveInteger"/> </xs:complexType> 168493: XML and Web Services (II/2546)

  37. Elements w/ Only Sub-Elements • XML:<p><fn>A</fn><ln>B</ln></p> • XSD: <xs:element name="p" type="persontype"/> <xs:complexType name="persontype"> <xs:sequence> <xs:element name="fn" type="xs:string"/> <xs:element name="ln" type="xs:string"/> </xs:sequence> </xs:complexType> 168493: XML and Web Services (II/2546)

  38. Elements w/ Only Text • XML: <shoesize>8</shoesize> • XSD: <xs:element name="shoesize" type="shoetype"/> <xs:complexType name="shoetype"> <xs:simpleContent> <xs:extension base="xs:integer"> … </xs:complexType> 168493: XML and Web Services (II/2546)

  39. Types w/ Mixed Content • XML: <letter>Today is <date>11.13.2003</date></letter> • XSD: <xs:element name="letter"> <xs:complexType mixed="true"> <xs:sequence> <xs:element name="shipdate" type="xs:date"/> … </xs:element> 168493: XML and Web Services (II/2546)

  40. Indicators • Order indicators: • All, choice, sequence • Occurrence indicators: • maxOccurs, minOccurs • Group indicators: • Group name • attributeGroup name 168493: XML and Web Services (II/2546)

  41. All Indicator • Specify by default that the child elements can appear in any order and each child element must occur once and only once <xs:element name=“person”> <xs:complexType> <xs:all> <xs:element name=“fname” type=“xs:string”/> … </xs:element> 168493: XML and Web Services (II/2546)

  42. Choice Indicator • Specify that either one child element or another can occur <xs:element name="person"> <xs:complexType> <xs:choice> <xs:element name="employee" type="employee"/> <xs:element name="member" type="member"/> ... </xs:element> 168493: XML and Web Services (II/2546)

  43. Sequence Indicator • Specify that the child elements must appear in a specific order <xs:element name="paper"> <xs:complexType> <xs:sequence> <xs:element name=“abstract" type="xs:string"/> <xs:element name=“introduction" type="xs:string"/> … </xs:element> 168493: XML and Web Services (II/2546)

  44. Occurrence Indicator • Define how often an element can occur • maxOccurs Indicator: maximum number of times an element can occur <xs:element name="person"> <xs:complexType> <xs:sequence> <xs:element name="full_name" type="xs:string"/> <xs:element name="child_name" type="xs:string" maxOccurs="10"/> … </xs:element> 168493: XML and Web Services (II/2546)

  45. Occurrence Indicator (Cont.) • minOccurs Indicator: minimum number of times an element can occur <xs:element name="person"> <xs:complexType> <xs:sequence> <xs:element name="full_name" type="xs:string"/> <xs:element name="child_name" type="xs:string" maxOccurs="10“ minOccurs=“0”/> … </xs:element> 168493: XML and Web Services (II/2546)

  46. Group Indicators • Define related sets of elements • Element Groups are defined with the group declaration, like this: <xs:group name=“groupname”> … </xs:group> • After defining a group, we can reference it in another complex type definition 168493: XML and Web Services (II/2546)

  47. Element Groups <xs:group name="persongroup"> <xs:sequence> <xs:element name="firstname" type="xs:string"/> … </xs:group> <xs:complexType name="personinfo"> <xs:sequence> <xs:group ref="persongroup"/> <xs:element name="country" type="xs:string"/> … 168493: XML and Web Services (II/2546)

  48. Attribute Groups <xs:attributeGroup name="personattrgroup"> <xs:attribute name="firstname" type="xs:string"/> … </xs:attributeGroup> <xs:element name="person"> <xs:complexType> <xs:attributeGroup ref="personattrgroup"/> … </xs:element> 168493: XML and Web Services (II/2546)

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