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Chapter 20 - Extensible Markup Language (XML)

Chapter 20 - Extensible Markup Language (XML). Outline 20.1 Introduction 20.2 Structuring Data 20.3 XML Namespaces 20.4 Document Type Definitions (DTDs) and Schemas 20.4.1 Document Type Definitions 20.4.2 W3C XML Schema Documents 20.5 XML Vocabularies 20.5.1 MathML

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Chapter 20 - Extensible Markup Language (XML)

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  1. Chapter 20 - Extensible Markup Language (XML) Outline 20.1 Introduction 20.2 Structuring Data 20.3 XML Namespaces 20.4 Document Type Definitions (DTDs) and Schemas 20.4.1 Document Type Definitions 20.4.2 W3C XML Schema Documents 20.5 XML Vocabularies 20.5.1 MathML 20.5.2 Chemical Markup Language (CML) 20.5.3 Other Markup Languages 20.6 Document Object Model (DOM) 20.7 DOM Methods 20.8 Simple API for XML (SAX) 20.9 Extensible Stylesheet Language (XSL) 20.10 Microsoft BizTalk 20.11 Simple Object Access Protocol (SOAP) 20.12 Internet and World Wide Web Resources

  2. XML markup • Documents written in XML describe their content using markup tags • XHTML markup only describes document structure • In XML tags are created to describe the document content – rendering of the content is a separate issue • A heirarchical structure is used for grouping properties together into larger entities

  3. Element article is the root element. Optional XML declaration. Elements title, date, author, summary and content are child elements of article. 1 <?xml version = "1.0"?> 2 3 <!-- Fig. 20.1: article.xml --> 4 <!-- Article structured with XML --> 5 6 <article> 7 8 <title>Simple XML</title> 9 10 <date>September 19, 2001</date> 11 12 <author> 13 <firstName>Tem</firstName> 14 <lastName>Nieto</lastName> 15 </author> 16 17 <summary>XML is pretty easy.</summary> 18 19 <content>Once you have mastered XHTML, XML is easily 20 learned. You must remember that XML is not for 21 displaying information but for managing information. 22 </content> 23 24 </article> Article.xml

  4. XML parsers • XML parsers support the Document Object Model (DOM) and/or Simple API for XML (SAX) interface • Internet Explorer will display XML documents with their structure • Specific application software may be written to interpret an XML document to display its contents appropriately • MathML can be viewed using Amaya or techexplorer • CML can be viewed using Jumbo

  5. 20.2 Structuring Data Fig. 20.2 IE5.5 displaying article.xml.

  6. XML Validation • In the same way that XHTML may be validated, XML should also be validated to ensure structural correctness • A document is validated with reference to its DOCTYPE specification • For XHTML the DOCTYPE is html and the specification is given by the xhtml11.dtd • For XML the DOCTYPE will define the structure of the data that is being recorded in the document

  7. Element flag is an empty element and does not contain any text. Information for the person writing the letter. Information for the person receiving the letter. 1 <?xml version = "1.0"?> 2 3 <!-- Fig. 20.3: letter.xml --> 4 <!-- Business letter formatted with XML --> 5 6 <!DOCTYPE letter SYSTEM"letter.dtd"> 7 8 <letter> 9 10 <contact type = "from"> 11 <name>John Doe</name> 12 <address1>123 Main St.</address1> 13 <address2></address2> 14 <city>Anytown</city> 15 <state>Anystate</state> 16 <zip>12345</zip> 17 <phone>555-1234</phone> 18 <flag gender = "M"/> 19 </contact> 20 21 <contact type = "to"> 22 <name>Joe Schmoe</name> 23 <address1>Box 12345</address1> 24 <address2>15 Any Ave.</address2> 25 <city>Othertown</city> 26 <state>Otherstate</state> 27 <zip>67890</zip> 28 <phone>555-4321</phone> 29 <flag gender = "M"/> 30 </contact> 31 Letter.xml

  8. Body of letter. Author’s signature. 32 <salutation>Dear Sir:</salutation> 33 34 <paragraph>It is our privilege to inform you about our new 35 database managed with XML. This new system allows 36 you to reduce the load of your inventory list server by 37 having the client machine perform the work of sorting 38 and filtering the data.</paragraph> 39 <closing>Sincerely</closing> 40 <signature>Mr. Doe</signature> 41 42 </letter> Letter.xmlProgram Output

  9. Program Output

  10. Avoiding XML name conflicts • It is possible that in a document the same name may be used for different types of object • This is resolved by using multiple namespace directives • Namespaces are declared as strings to distinguish between different types of objects • The namespaces are in the form of uniform resource identifiers (URIs) which can either be Uniform Resource Names (URNs) or Uniform Resource Locations (URLs) • They are not visited by the parser, so do not need to exist in reality – they are merely there to distinguish between the XML tags

  11. Keyword xmlns creates two namespace prefixes, text and image. URIs ensure that a namespace is unique. 1 <?xml version = "1.0"?> 2 3 <!-- Fig. 20.4 : namespace.xml --> 4 <!-- Demonstrating Namespaces --> 5 6 <text:directory xmlns:text = "urn:deitel:textInfo" 7 xmlns:image = "urn:deitel:imageInfo"> 8 9 <text:file filename = "book.xml"> 10 <text:description>A book list</text:description> 11 </text:file> 12 13 <image:file filename = "funny.jpg"> 14 <image:description>A funny picture</image:description> 15 <image:size width = "200" height = "100"/> 16 </image:file> 17 18 </text:directory> Namespace.xml

  12. XML default name space • A default namespace can be assigned to the document • Any unqualified tags correspond to the default namespace

  13. Default namespace. Element file uses the default namespace. Element file uses the namespace prefix image. 1 <?xml version = "1.0"?> 2 3 <!-- Fig. 20.5 : defaultnamespace.xml --> 4 <!-- Using Default Namespaces --> 5 6 <directory xmlns = "urn:deitel:textInfo" 7 xmlns:image = "urn:deitel:imageInfo"> 8 9 <file filename = "book.xml"> 10 <description>A book list</description> 11 </file> 12 13 <image:file filename = "funny.jpg"> 14 <image:description>A funny picture</image:description> 15 <image:size width = "200"height = "100"/> 16 </image:file> 17 18 </directory> Defaultnamespace.xml

  14. XML document type definition (DTD) • Validity of an XML document depends upon the correctly parsed content conforming to the document type definition • The DTD is specified in the DOCTYPE directive • DTDs may be specified within the XML document itself, or as an external dtd file <!DOCTYPE myMessage [ <!ELEMENT myMessage ( #PCDATA )> ]> <!DOCTYPE myMessage SYSTEM "myDTD.dtd">

  15. The ELEMENT element type declaration defines the rules for element letter. The plus sign (+) occurrence indicator specifies that the DTD allows one or more occurrences of an element. The contact element definition specifies that element contact contains child elements name, address1, address2, city, state, zip, phone and flag—in that order. Keyword #IMPLIED specifies that if the parser finds a contact element without a type attribute, the parser can choose an arbitrary value for the attribute or ignore the attribute and the document will be valid. Flag #PCDATA specifies that the element can contain parsed character data (i.e., text). The ATTLISTelement type declaration defines an attribute (i.e., type) for the contact element. 1 <!-- Fig. 20.4: letter.dtd --> 2 <!-- DTD document for letter.xml --> 3 4 <!ELEMENT letter ( contact+, salutation, paragraph+, 5 closing, signature )> 6 7 <!ELEMENT contact ( name, address1, address2, city, state, 8 zip, phone, flag )> 9 <!ATTLIST contact type CDATA #IMPLIED> 10 11 <!ELEMENT name ( #PCDATA )> 12 <!ELEMENT address1 ( #PCDATA )> 13 <!ELEMENT address2 ( #PCDATA )> 14 <!ELEMENT city ( #PCDATA )> 15 <!ELEMENT state ( #PCDATA )> 16 <!ELEMENT zip ( #PCDATA )> 17 <!ELEMENT phone ( #PCDATA )> 18 <!ELEMENT flag EMPTY> 19 <!ATTLIST flag gender (M | F) "M"> 20 21 <!ELEMENT salutation ( #PCDATA )> 22 <!ELEMENT closing ( #PCDATA )> 23 <!ELEMENT paragraph ( #PCDATA )> 24 <!ELEMENT signature ( #PCDATA )> Letter.dtd

  16. Combining terms Sequence: ( item1, item2 ) Selection: ( item1 | item2 ) One or more: item1+ Zero or more: item1* Zero or one: item1? EMPTY specifies the element has no content ANY matches any content, including empty content #PCDATA matches parsable character data XML DTD specification

  17. Attributes are associated with XML tag names <message id="24"> has a single attribute and would be defined with <!ATTLIST message id CDATA #IMPLIED> CDATA matches character data (no <, >, &, ' or " allowed) #REQUIRED means an attribute must be present #IMPLIED means an attribute may be unspecified #FIXED means an attribute must have the specified value if present ID a unique token IDREF reference to an ID XML attributes

  18. Schemas and DTDs • DTDs are inflexible in that the order of elements can be significant • Also DTDs have no way of validating the content of an element • Different Schemas exist – Microsoft and W3C • Microsoft schemas define ElementType entities, with information as to the element content in attributes • For example content could be textOnly, eltOnly, empty or mixed • The order can be one, seq or many

  19. W3C XML schema • Syntax is the same as an XML document, thus it can be parsed as XML • All tag names start with xsd: • Element names are defined in terms of types • Types are defined in terms of content within that type • As for Microsoft Schema the minOccurs and maxOccurs specify how many times the element is repeated within the given type

  20. 1 <?xml version = "1.0"?> 2 <!-- Fig. 20.7 : book.xml --> 3 <!-- Book list marked up as XML --> 4 5 <deitel:books xmlns:deitel = "http://www.deitel.com/booklist"> 6 <book> 7 <title>XML How to Program</title> 8 </book> 9 <book> 10 <title>C How to Program</title> 11 </book> 12 <book> 13 <title>Java How to Program</title> 14 </book> 15 <book> 16 <title>C++ How to Program</title> 17 </book> 18 <book> 19 <title>Perl How to Program</title> 20 </book> 21 </deitel:books> Book.xmlProgram Output java -classpath .;..\lib\xmlparserv2.jar;..\lib\xschema.jar XSDSetSchema book.xsd book.xml The input file <book.xml> parsed without errors

  21. Attributes name and type specify the element’s name and data type, respectively. Element element defines an element to be included in the XML document structure. Element complexType defines an element type that has a child element named book. Attribute minOccurs specifies that books must contain a minimum of one book element. Attribute maxOccurs, with value unbounded specifies that books may have any number of book child elements. 1 <?xml version = "1.0"?> 2 3 <!-- Fig. 20.8 : book.xsd --> 4 <!-- Simple W3C XML Schema document --> 5 6 <xsd:schema xmlns:xsd = "http://www.w3.org/2000/10/XMLSchema" 7 xmlns:deitel = "http://www.deitel.com/booklist" 8 targetNamespace = "http://www.deitel.com/booklist"> 9 10 <xsd:element name = "books" type = "deitel:BooksType"/> 11 12 <xsd:complexType name = "BooksType"> 13 <xsd:element name = "book" type = "deitel:BookType" 14 minOccurs = "1" maxOccurs = "unbounded"/> 15 </xsd:complexType> 16 17 <xsd:complexType name = "BookType"> 18 <xsd:element name = "title" type = "xsd:string"/> 19 </xsd:complexType> 20 21 </xsd:schema> Book.xsd

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