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XML Schemas

XML Schemas. Useful Links. Schema tutorial links: http://www.w3schools.com/schema/default.asp http://www.xfront.com/ http://www.w3.org/TR/xmlschema-0/. Why Schemas. Enhanced datatypes 44+ versus 10 Can create your own datatypes

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XML Schemas

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  1. XML Schemas

  2. Useful Links • Schema tutorial links: • http://www.w3schools.com/schema/default.asp • http://www.xfront.com/ • http://www.w3.org/TR/xmlschema-0/

  3. Why Schemas • Enhanced datatypes • 44+ versus 10 • Can create your own datatypes • Example: "This is a new type based on the string type and elements of this type must follow this pattern: ddd-dddd, where 'd' represents a digit". • Written in the same syntax as instance documents: less syntax to remember • Can extend or restrict a type (derive new type definitions on the basis of old ones) • Can express sets, i.e., can define the child elements to occur in any order • Can specify element content as being unique (keys on content) and uniqueness within a region • Can define multiple elements with the same name but different content • Can define substitutable elements - e.g., the "Book" element is substitutable for the "Publication" element.

  4. Schemas and DTDs • One difference between XML Schemas and DTDs is that the XML Schema vocabulary is associated with a name (namespace). Likewise, the new vocabulary that you define must be associated with a name (namespace). • With DTDs neither set of vocabulary is associated with a name (namespace).

  5. Some XML Parsers with Schema Support • A comparison of some XML parsers: • http://webreference.com/xml/column22/2.html

  6. Example – BookCatalog.dtd • <!ELEMENT BookCatalog (Book)+> • <!ELEMENT Book (Title, Author, Date, ISBN, Publisher)> • <!ELEMENT Title (#PCDATA)> • <!ELEMENT Author (#PCDATA)> • <!ELEMENT Date (#PCDATA)> • <!ELEMENT ISBN (#PCDATA)> • <!ELEMENT Publisher (#PCDATA)>

  7. An Example Of A Schema DefinitionBookCatalog.xsd <?xml version="1.0" encoding="UTF-8"?> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="BookCatalog"> <xsd:complexType> <xsd:sequence> <xsd:element ref="Book" minOccurs="1“ maxOccurs="unbounded"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="Book"> <xsd:complexType> <xsd:sequence> <xsd:element ref="Title" minOccurs="1" maxOccurs="1"/> <xsd:element ref="Author" minOccurs="1" maxOccurs="1"/> <xsd:element ref="Date" minOccurs="1" maxOccurs="1"/> <xsd:element ref="ISBN" minOccurs="1" maxOccurs="1"/> <xsd:element ref="Publisher" minOccurs="1" maxOccurs="1"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="Title" type="xsd:string"/> <xsd:element name="Author" type="xsd:string"/> <xsd:element name="Date" type="xsd:string"/> <xsd:element name="ISBN" type="xsd:string"/> <xsd:element name="Publisher" type="xsd:string"/> </xsd:schema>

  8. BookCatalog.xml <?xml version="1.0"?> <BookCatalog xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="BookCatalog.xsd"> <Book> <Title>Billions Of Stars</Title> <Author>Susan Boggs</Author> <Date>1983</Date> <ISBN>1-5555-555-2</ISBN> <Publisher>Anderson-Wells</Publisher> </Book> <Book> <Title>Adventures Of Freddie the Frog</Title> <Author>John Smith</Author> <Date>1977</Date> <ISBN>0-444-4444-4</ISBN> <Publisher>Kidder Publishing Co.</Publisher> </Book> </BookCatalog>

  9. Schema namespace • Schema element: All XML schemas have schema as the root element. • XML Schema namespace: The elements and datatypes that are used to construct schemas, like, schema, element, complexType, sequence and string come from the http://…/XMLSchema namespace

  10. Using namespacesExample – plants.xsd <?xml version="1.0"?> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.MyDefs.com" xmlns="http://www.MyDefs.com" elementFormDefault="qualified"> <xsd:element name="plants"> <xsd:complexType> <xsd:sequence> <xsd:element ref="plant" minOccurs="1" maxOccurs="unbounded"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="plant"> <xsd:complexType> <xsd:sequence> <xsd:element name="plantName" minOccurs="1" maxOccurs="1"/> <xsd:element name="category" minOccurs="1" maxOccurs="1"/> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:schema>

  11. Example – plants.xml <?xml version="1.0"?> <plants xmlns="http://www.MyDefs.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=“plants.xsd"> <plant> <plantName>Daisy</plantName> <category>perennial</category> </plant> </plants>

  12. Example – BookCatalog.xsd <?xml version="1.0"?> <schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.MyDefs.org" xmlns:bk="http://www.MyDefs.org" elementFormDefault="qualified"> <element name="BookCatalog"> <complexType> <sequence> <element ref="bk:Book" minOccurs="1" maxOccurs="unbounded"/> </sequence> </complexType> </element> <element name="Book"> <complexType> <sequence> <element ref="bk:Title"/> … <element ref="bk:Publisher"/> </sequence> </complexType> </element> <element name="Title" type="string"/> … <element name="Publisher" type="string"/> </schema>

  13. BookCatalog.xml <?xml version="1.0"?> <BookCatalog xmlns="http://www.MyDefs.org" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.MyDefs.org BookCatalog.xsd"> <Book> <Title>Billions Of Stars</Title> <Author>Susan Boggs</Author> <Date>1983</Date> <ISBN>1-5555-555-2</ISBN> <Publisher>Anderson-Wells</Publisher> </Book> <Book> <Title>Adventures Of Freddie the Frog</Title> <Author>John Smith</Author> <Date>1977</Date> <ISBN>0-444-4444-4</ISBN> <Publisher>Kidder Publishing Co.</Publisher> </Book> </BookCatalog>

  14. Simple vs Complex Types • A schema document can be divided into content types: Simple and complex types. • Simple types: can contain only text. There are several simple built-in types – String, Boolean, Float, Double, ID, IDREF, Entity etc. • Derived data types: The built-in data types can be customized to control the content. • Complex types: can contain elements that can contain other elements or attributes. • Local vs global declarations: Schema components, elements, attributes, named simple and complex types, declared under xsd:schema element are considered globally declared. A global declaration has to be explicitly referenced. • New elements can be declared within the context of a complex type, in which case they are considered locally declared.

  15. Simple Types: exampleA.xsd <?xml version="1.0" encoding="UTF-8"?> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="SimpleTypes"/> <xsd:element name="title" type="xsd:string"/> <xsd:element name="price" type="xsd:decimal"/> <xsd:element name="last-modified" type="xsd:string"/> <xsd:element name="translated" type="xsd:boolean"/> </xsd:schema>

  16. exampleA.xml <?xml version="1.0"?> <SimpleTypes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="exampleA.xsd"> <title>Billions Of Stars</title> <price>2000-01-02</price> <lastModified>1983</lastModified> <translated>true</translated> </SimpleTypes>

  17. Deriving From Simple Types • A new custom type can be derived a simple type. • Example: <xsd:simpleType name="ISBNType"> <xsd:restriction base="xsd:string"> -- refers to a simple type <xsd:pattern value="\d{1}-\d{5}-\d{3}-\d{1}"/> </xsd:restriction> </xsd:simpleType> • Patterns are specified using regular expressions (supports regular expressions from perl)

  18. <?xml version="1.0" encoding="UTF-8"?> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="CustomTypes"/> <xsd:simpleType name="ISBNType"> <xsd:restriction base="xsd:string"> <xsd:pattern value="\d{1}-\d{5}-\d{3}-\d{1}"/> </xsd:restriction> </xsd:simpleType> <xsd:element name="title" type="xsd:string"/> <xsd:element name="ISBN" type="ISBNType"/> </xsd:schema> <?xml version="1.0"?> <CustomTypes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="exampleB.xsd"> <title>Billions Of Stars</title> <ISBN> 2-12345-678-9 </ISBN> </CustomTypes> Example – Example3.xsd and Example3.xml

  19. Giving a choice of acceptable values <xsd:simpleType> <xsd:restriction base="xsd:string"> <xsd:enumeration value="autobiography"/> <xsd:enumeration value="non-fiction"/> <xsd:enumeration value="fiction"/> </xsd:restriction> </xsd:simpleType>

  20. Defining Complex Types • Elements that can contain other elements or attributes. • There are four kinds of elements of complex type: • Elements that contain other elements and attributes, but no text. • Elements that are empty – possibly contain attributes but no other elements or text. • Elements of mixed content that can contain a combination of elements, attributes or text. • Elements that contain only text.

  21. Example - Elements containing elements only <?xml version="1.0"?> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="BookCatalog"> <xsd:complexType> <xsd:sequence> <xsd:element name="Book" maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence> <xsd:element name="Title" type="xsd:string"/> <xsd:element name="Author" type="xsd:string"/> …. </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:schema>

  22. Example – Elements containing elements only <?xml version="1.0" encoding="UTF-8"?> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="plants"> <xsd:complexType> <xsd:sequence> <xsd:element ref="plant" minOccurs="1" maxOccurs="unbounded"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="plant"> <xsd:complexType> <xsd:sequence> <xsd:element name="plantName" minOccurs="1" maxOccurs="1"/> <xsd:element name="category" minOccurs="1" maxOccurs="1"/> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:schema>

  23. Referring to a group If we want to reuse a set of elements in several content –type definitions, we can use a model group to define a set of elements that can be repeated. They act rather like parameter entities in DTDs. A model group consists of element declarations, wildcards and other model groups. The minimum values for min and maxOccurences = 1. <xsd:element name="Book" maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence> <xsd:group ref="BookElements"/> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:group name="BookElements"> <xsd:sequence> <xsd:element name="Title" type="xsd:string"/> <xsd:element name="Author" type="xsd:string" maxOccurs="unbounded"/> <xsd:element name="Date" type="xsd:string"/> <xsd:element name="ISBN" type="xsd:string"/> <xsd:element name="Publisher" type="xsd:string"/> </xsd:sequence> </xsd:group>

  24. <xsd:element name="Book" maxOccurs="unbounded"> <xsd:complexType> <xsd:all> <xsd:element name="Title" type="xsd:string"/> <xsd:element name="Author" type="xsd:string"/> <xsd:element name="Date" type="xsd:string"/> <xsd:element name="ISBN" type="xsd:string"/> <xsd:element name="Publisher" type="xsd:string"/> </xsd:all> </xsd:complexType> </xsd:element> <?xml version="1.0"?> <Book> <Title>Billions Of Stars</Title> <Author>Susan Boggs</Author> <Date>1983</Date> <ISBN>1-5555-555-2</ISBN> <Publisher>Anderson-Wells</Publisher> </Book> <Book> <Title>Adventures Of Freddie the Frog</Title> <Author>John Smith</Author> <Date>1977</Date> <ISBN>0-444-4444-4</ISBN> <Publisher>Kidder Publishing Co.</Publisher> </Book> </BookStore> Using all

  25. Attributes • Attribute declarations: • An attribute is declared with <attribute>. • An attribute can be defined outside of a complex type and referenced in complex type. • Attribute types can be defined using primitive types. • Default, fixed, optional, required and prohibited can be used to set the values for attributes. • Example: • <attribute name=widgetPrice” type=“xsd:float” value=“10.00” use=“required” />

  26. <!ELEMENT BookCatalog(Book)+> <!ELEMENT Book (Title, Author+, Date, ISBN, Publisher)> <!ATTLIST Book Category (autobiography | non-fiction | fiction) #REQUIRED InStock (true | false) "false" Reviewer CDATA " "> <!ELEMENT Title (#PCDATA)> <!ELEMENT Author (#PCDATA)> <!ELEMENT Date (#PCDATA)> <!ELEMENT ISBN (#PCDATA)> <!ELEMENT Publisher (#PCDATA)> <!ELEMENT Month (#PCDATA)> <!ELEMENT Year (#PCDATA)>

  27. <xsd:element name="BookCatalog"> <xsd:complexType> <xsd:sequence> <xsd:element name="Book" maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence> <xsd:element name="Title" type="xsd:string"/> <xsd:element name="Author" type="xsd:string" maxOccurs="unbounded"/> <xsd:element name="Publisher" type="xsd:string"/> </xsd:sequence> <xsd:attributeGroup ref="BookAttributes"/> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:attributeGroup name="BookAttributes"> <xsd:attribute name="Category" use="required"> <xsd:simpleType> <xsd:restriction base="xsd:string"> <xsd:enumeration value="autobiography"/> <xsd:enumeration value="non-fiction"/> <xsd:enumeration value="fiction"/> </xsd:restriction> </xsd:simpleType> </xsd:attribute> <xsd:attribute name="InStock" type="xsd:boolean" default="false"/> <xsd:attribute name="Reviewer" type="xsd:string" default="none"/> </xsd:attributeGroup> </xsd:schema>

  28. Uniqueness & Keys • DTDs provide the ID attribute datatype for uniqueness (i.e., an ID value must be unique throughout the entire document, and the XML parser enforces this). • XML Schema has much enhanced uniqueness capabilities: • enables you to define element content to be unique. • enables you to define non-ID attributes to be unique. • enables you to define a combination of element content and attributes to be unique. • enables you to distinguish between unique versus key. • enables you to declare the range of the document over which something is unique

  29. unique vs key • Key: an element or attribute (or combination thereof) which is defined to be a key must: • always be present (minOccurs must be greater than zero) • be not-false. • be unique • Key implies unique, but unique does not imply key

  30. Using ISBN as a Key • In the next example, we will use a Book's ISBN element as a key.

  31. Example <?xml version="1.0"?> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.MyDefs.com" xmlns="http://www.myDefs.com" xmlns:bk="http://www.MyDefs.com" elementFormDefault="qualified"> <xsd:element name="BookCatalog"> <xsd:complexType> <xsd:sequence> <xsd:element name="Book" maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence> <xsd:element name="Title" type="xsd:string"/> <xsd:element name="Author" type="xsd:string"/> <xsd:element name="Date" type="xsd:string"/> <xsd:element name="ISBN" type="xsd:string"/> <xsd:element name="Publisher" type="xsd:string"/> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType> <!-- Within <BookCatalog> define a key, called PK. Select each <Book>, and within each <Book> the ISBN element is a key.“  <xsd:key name="PK"> <xsd:selector xpath="bk:Book"/> <xsd:field xpath="bk:ISBN"/> </xsd:key> </xsd:element> </xsd:schema>

  32. BookCatalog.xml <?xml version="1.0"?> <BookCatalog xmlns="http://www.MyDefs.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation= "http://www.MyDefs.com BookCatalog.xsd"> <Book> <Title>Billions Of Stars</Title> <Author>Susan Boggs</Author> <Date>1983</Date> <ISBN>1-5555-555-2</ISBN> <Publisher>Anderson-Wells</Publisher> </Book> <Book> <Title>Adventures Of Freddie the Frog</Title> <Author>John Smith</Author> <Date>1977</Date> <ISBN>0-444-4444-4</ISBN> <Publisher>Kidder Publishing Co.</Publisher> </Book> </BookCatalog>

  33. Notes about <key> • It must be nested within an <element> • It must come at the end of <element> (after the content model, and attribute declarations) • Use the <selector> element as a child of <key> to select a set of elements for which the key applies. • Use the <field> element as a child of <key> to identify the element or attribute that is to be the key • There can be multiple <field> elements.

  34. Example – meeting.xsd <xsd:element name="meeting"> <xsd:complexType> <xsd:sequence> <xsd:element name="participants"> <xsd:complexType> <xsd:sequence> <xsd:element name="Name" minOccurs="0" maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence> <xsd:element name="First" type="xsd:string"/> <xsd:element name="Last" type="xsd:string"/> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:sequence> </xsd:complexType> <!-- The key is the combination of the First and Last name.  <xsd:key name="PK"> <xsd:selector xpath="meet:participants/meet:Name"/> <xsd:field xpath="meet:First"/> <xsd:field xpath="meet:Last"/> </xsd:key> </xsd:element>

  35. Example-meeting.xml <?xml version="1.0"?> <meeting xmlns="http://www.MyDefs.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.MyDefs.com Meeting.xsd"> <participants> <Name><First>John</First><Last>Smith</Last></Name> <Name><First>Mary</First><Last>Jones</Last></Name> </participants> </meeting>

  36. unique • The <unique> element is used exactly like the <key> element is used. It has a <selector> and one or more <field> elements, just like <key> has. • The only difference is that the schema validator will simply validate that, whenever present, the values are unique.

  37. Example <?xml version="1.0"?> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.MyDefs.com" xmlns="http://www.myDefs.com" xmlns:bk="http://www.MyDefs.com" elementFormDefault="qualified"> <xsd:element name="BookCatalog"> <xsd:complexType> <xsd:sequence> <xsd:element name="Book" maxOccurs="unbounded"> …. </xsd:complexType> <!– ISBN are unique  <xsd:unique name="UNIQ"> <xsd:selector xpath="bk:Book"/> <xsd:field xpath="bk:ISBN"/> </xsd:unique> </xsd:element> </xsd:schema>

  38. Referencing a key with a key ref • Similar to ID/IDREFS, you can define a keyref to link an element with a key. • If there are 2 fields in the key, then there must be 2 fields in the keyref, if there are 3 fields in the key, then there must be 3 fields in the keyref, etc. • Further, the fields in the keyref must match in type and position to the key.

  39. Example – keyRef.xsd <xsd:element name="rootElement"> <xsd:complexType> <xsd:sequence> <xsd:element name="elementOne" maxOccurs="unbounded"> <xsd:complexType> <xsd:attribute name="elementOneKey" type="xsd:integer" /> <xsd:attribute name="elementOneDesc" type="xsd:string" /> </xsd:complexType> <xsd:key name="elementOnePK"> <xsd:selector xpath=".//elementOne"/> <xsd:field xpath="@elementOneKey"/> </xsd:key> </xsd:element> <xsd:element name="elementTwo" maxOccurs="unbounded"> <xsd:complexType> <xsd:attribute name="elementTwoKey" type="xsd:integer" /> <xsd:attribute name="elementOneKey" type="xsd:integer" /> <xsd:attribute name="elementTwoDesc" type="xsd:string" /> </xsd:complexType> <xsd:keyref name="elementOneFK" refer="elementOnePK"> <xsd:selector xpath=".//elementTwo"/> <xsd:field xpath="@elementOneKey"/> </xsd:keyref> </xsd:element> </xsd:sequence> </xsd:complexType> </xsd:element>

  40. Example – keyRef.xml <?xml version="1.0"?> <rootElement xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="Keyref.xsd"> <elementOne elementOneKey="11" elementOneDesc="Some"/> <elementOne elementOneKey="12" elementOneDesc="Other"/> <elementTwo elementTwoKey="99" elementOneKey="11" elementTwoDesc="Refers To Some"/> <elementTwo elementTwoKey="100" elementOneKey="12" elementTwoDesc="Refers To Other"/> </rootElement>

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