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XML eXtensible Markup Language
by Darrell Payne
Experience Logicon / Sterling Federal
C, C++, JavaScript/Jscript, Shell Script, Perl XML Training
XML Training Course 2001 DevXCon Training Conference Currently developing XML course for
Logicon [email protected]
XML eXtensible Markup Language Standard General Markup Language(SGML)
Meta-tag language Used for creating other markup languages
Standard adopted for SGML in 1986 Hyper Text Markup Language(HTLM)
Application of SGML Formatting Language
eXtensible Markup Language(XML) Meta-tag language XML = DATA World Wide Web Consortium W3C
((!Standard) && (Specification)) // “c” code humor XML Version 1.0 February 1998 XML is not designed to replace HTML
SGML – HTML – XML diagram
SGML XML
HTMLapplication
WMLapplication
XML Family of Tools and Their Relationship
Namespace
SAXDOM
XMLInfo set
XMLSchema
XPath XSL
XSLTXPointer
XLinkStyle andTransformation
Linking andPointing
UnderlyingAndObjectModel
ProgrammaticInterface
ComplexData Modeling
XML Developer's Guide - McGraw Hill - Page 12
HTML vs. XML Html
Predefined tags Syntax is loose File extensions usually “.html” of “.htm” Not required to be Well – Formed
Some closing tags optional Attribute value quotes may be omitted
XML User defined tags Syntax is exact File extensions usually “.xml” Closing tags mandatory Required to be Well - Formed
Well - Formed All XML documents must be
Syntactically correct! Single root element All element start tags have end tags XML is case sensitive Properly nested tags
<first><second></first></second> //error <first><second></second></first> //correct
Attributes values in quotes “value“ or ‘value‘
Basic XML Parts Markup
Tags Attributes, names and values
Character Data Text
PCDATA CDATA
Binary XML document has two main sections
Prolog Root Misc
Optional and considered superfluous
Simple XML File
<?xml version="1.0"?> <!-- My first XML file --> <document> <message>Hello World!</message > </document > <!-- More Comments -->
Declaration If used: <?xml version="1.0"?> required
Declaration optional Specifies version to which document conforms XML documents without XML declaration might be assumed to
conform to the latest version Other declaration examples <?xml version="1.0" encoding="UTF-8"?> optional
Default – Good for ASCII text – 8 bit characters “UTF-16” Good for foreign – 16 bit characters
Used for Unicode characters To stay uniform use with 8 or 16
<?xml version="1.0" standalone="yes"?> optional No external subset referenced – default
<?xml version="1.0" encoding=“UTF-8” standalone="yes”?>
Comments
<!-- My first XML file --> <!-- More Comments -->
XML uses same comment syntax as HTML
Root Element
<document>
</document> Lines preceding root element are contained in the
Prolog All XML documents must contain only one root
element All other elements are “child element”s
Child Element
<document> <message>Hello World!</message > </document >
Sibling Element
<document> <message>Hello World!</message > <message>Goodbye World!</message > <message2>Nothing more to
add!</message2 > </document >
Updating Microsoft’s Internet Explorer instmsia.exe
Updates Microsoft’s Installer
msxml3sp1.exe Updates Microsoft’s Internet Explorer
IE now has built-in XML parser “msxml”
Create XML Document Include declaration
<?xml version="1.0"?>
Create root element <cis_class> Create child element <cis_345> Enter child element text “student name” Save file with “.xml” extension Open using Internet Explorer After success, add siblings elements and
retest using Internet Explorer
Document viewed in Microsoft's Internet Explorer
More about Elements Element types
Container Element Contains other elements
Data Element Contains DATA
Mixed Content Contains other elements and DATA
Empty Element Contains no elements or DATA
Container Element Contains other elements <outer_element>
<inner_element> <yet_another_element>
<can_we_go_any_deeper> Some text way down here in the center of it all
</can_we_go_any_deeper> </yet_another_element>
</inner_element> </outer_element>
Data Element Contains DATA
Parsable Character Data PCDATA
Character Data CDATA
PCDATA Contains text Can be parsed by parser Can contain all text except
< > “ ‘ &
Entity References XML provides built in entity
references < > " ' &
CDATA Contains text Is a declaration Can contain reserved characters
<, >, “, ‘, & Starts with / ends with
<![CDATA[ Data would be here
]]> CDATA can not contain
]]>
Declarations <!-- --> <!DOCTYPE > <![CDATA[ ]]> <!ELEMENT > <![IGNORE[ ]]> <![INCLUDE[ ]]> <!NOTATION > <!ENTITY > <!ATTLIST >
Why CDATA section “C++” code example
CDATA example If (this->getX() < 5 && array1[0] != 3) cerr << this->displayError();
PCDATA example If (this->getX() < 5 && array1[0] != 3) cerr << this->displayError();
Mixed Content Elements and PCDATA combined <outer_element>
outer element stuff <inner_element>
inner element stuff </inner_element>
more outer element stuff </outer_element>
Empty Element Contains no text or data May have an attribute <empty_element></empty_element> <empty_element/>
Short cut notation for empty element Does this look unfamiliar
HTML example of such a type of tag <img src = “image.gif”> //Non Well Formed <img src = “image.gif” /> //Well Formed
Elements
element
Start-tag
content
End-tag
Create XML Document 2 Include declaration Create root element <cis_class2> Create child element <cis_345>
Enter child element text “student name” Create child element <cis_346>
Child to root, sibling to <cis_345> Make this an empty element
Create child element <cis_347> Child to root, sibling to <cis_345> Enter C++ code example in PCDATA section
Create child element <cis_348> Enter same C++ code in a CDATA section
Save file Open using Internet Explorer
XML Parser – DOM & SAX Required to process an XML document C, Java, Python, Perl Parsers are of type
Document Object Model(DOM) Tree structure Like a drive directory structure Slower and requires large amounts of memory
Simple API for XML(SAX) Events driven Events = tags, text, etc. Smaller, faster, but requires programmer to deal with data
Validating and non-validating
XML Structure Logical structure
Document divided into units Allows sub units XML is a logical tree structure
document Physical structure
Data stored inside document Data stored outside document
Entities one example
Valid Conforms to some schema
schema “s” Document Type Definition(DTD) Schema
By definition, all valid XML documents are Well – Formed documents
DTD Document Type Definition Document Type Declaration(DTD) File extension of “.dtd” DTD is not an XML document DTD is a schema “s” Introduced into an XML document via the Document Type
Declaration <!DOCTYPE >
Three types of DOCTYPE declarations Internal Subset
Contained in the Prolog External Subset
Exist in different file Prolog contains reference to file containing DTD Referenced using key work
SYSTEM or PUBLIC Internal Subset and External Subset combination
Internal Subset <?xml version="1.0"?> <!-- My second XML file --> <!DOCTYPE document [ <!ELEMENT document (message)> <!ELEMENT message (#PCDATA)> ]> <document> <message>Hello World!</message> </document> <!-- More Comments -->
External Subset <?xml version="1.0"?> <!-- My second XML file --> <!DOCTYPE document SYSTEM
"HelloWorld.dtd"> <document> <message>Hello World!</message> </document> <!-- More Comments -->
DTD for HelloWorld.xml <!ELEMENT document (message)> <!ELEMENT message (#PCDATA)>
Internal Subset and External Subset combination I <?xml version="1.0"?> <!-- My second XML file --> <!DOCTYPE document SYSTEM "HelloWorld3.dtd"[ <!ELEMENT document (message)> ]> <document> <message > <message2> </message2> </message> </document> <!-- More Comments -->
Internal Subset and External Subset combination II <!-- External declarations --> <!ELEMENT message (message2)> <!ELEMENT message2 (#PCDATA)>
Putting it all together HelloWorld3.dtd
<!-- External declarations --> <!ELEMENT message (message2)> <!ELEMENT message2 (#PCDATA)>
HelloWorld3.xml <?xml version="1.0"?> <!-- My second XML file --> <!DOCTYPE document SYSTEM "HelloWorld3.dtd"[ <!ELEMENT document (message)> ]> <document> <message > <message2> </message2> </message> </document> <!-- More Comments -->
XML ValidatorType in HelloWorld3.xml
Create XML Document 3 Create root element <session1> Create child element of session1<session2>
Enter child element text “xml class” Create child element of session2<session3>
Enter child element text “class information” Create child element of session3<session4>
Enter child element text “more” Create DTD for this file dtd_info.dtd
Reference file in XML document Save files Open validate_vbs.html Enter .xml file name Validate
Schema Schemas are XML documents
Schemas can be manipulated via a parser
More complicated than DTDs Schemas have “ElementType”s
Schema vs. DTD <!-- External declarations --> <!ELEMENT document (message, message2,
message3)> <!ELEMENT message (message4,
message5 )> <!ELEMENT message2 (#PCDATA)> <!ELEMENT message3 (#PCDATA)> <!ELEMENT message4 (#PCDATA)> <!ELEMENT message5 (#PCDATA)>
Schema vs. DTD II <?xml version="1.0" encoding="UTF-8"?> <!--W3C Schema generated by XML Spy v3.5
(http://www.xmlspy.com)--> <xsd:schema
xmlns:xsd="http://www.w3.org/2000/10/XMLSchema" elementFormDefault="qualified">
<xsd:element name="document"> <xsd:complexType> <xsd:sequence> <xsd:element ref="message"/> <xsd:element ref="message2"/> <xsd:element ref="message3"/> </xsd:sequence> </xsd:complexType> </xsd:element>
Schema vs. DTD III <xsd:element name="message"> <xsd:complexType> <xsd:sequence> <xsd:element ref="message4"/> <xsd:element ref="message5"/> </xsd:sequence> </xsd:complexType> </xsd:element> <xsd:element name="message2" type="xsd:string"/> <xsd:element name="message3" type="xsd:string"/> <xsd:element name="message4" type="xsd:string"/> <xsd:element name="message5" type="xsd:string"/> </xsd:schema>
Topics not covered Namespace Whitespace Xpath Xpointer Xlink XSL XSLT SOAP DDI Web Services SMIL XHTML