Introduction to XML Part 2

1
Introduction to XMLPart 2

• Zdenek abokrtský
• (using examples from www.kosek.cz)?

2
Jmenné prostory

• v jednom dokumentu se mohou mísit tagy popsané
  napr. v ruzných DTD,
• fragmenty textu formátovaného v HTML vloené do
  jiného XML
• tagy pro transformacní instrukce smíené s tagy
  transformovaného dokumentu atd.
• význam tagu nesmí být nejednoznacný, je treba
  vyreit duplikaci jmen elementu a atribututu z
  ruzných schémat
• Namespaces in XML doporucení W3C, 1999
• poskytuje mechanismus pro identifikaci jmenných
  prostoru pouitých v dokumentu
• umoní identifikovat, ke kterému jmennému
  prostoru daný element nebo atribut patrí

3
Jmenné prostrory, pokrac.

• jako identifikátor jmenného prostoru se pouívá
  URL
• jednoznacnost
• ocekávaná informativní hodnota (na URL naleznu o
  daném jmenném prostoru více informace)
• Pozor formálne jde stále pouze o identifikátor!
  aplikace nebudou vyadovat prístup k internetu a
  dané URL ve skutecnosti nemusí ani existovat!
• plne kvalifikované jméno (atributu/elementu)?
• prefixjmeno
• zavedení prefixu atribut xmlnsprefix
• pokud jeden namespace dominuje, lze pouít
  prázdný prefix
• ltkniha xmlnshttp//ufal.mff.cuni.cz/kniha
  xmlnsbibhttp//www.book.org/bibliographygt ...
  ltkapitolagt ... ltbibbookgtltbibauthorgt..

4
Navigation in XML

• Dokument addressing
• URL (Universal Resource Locator)?
• i.e. usual protocol//compport/path/resource
• Navigation inside a document
• Using identifiers relation between ID and IDREF
• Xpath
• Xlink, XPointer

5
XPath

• Result of a query in XPath applied on a given XML
  document is a set of nodes of the document
  matching the query
• XML document is understood as a tree structure
  containing nodes of three types elements,
  attributes, text
• XPath syntax very similar to addressing in file
  systems
• Examples
• /book root element named book
• /book/chapter all elements named chapter in
  the root element book
• /book/ - all elements in the book root element

6
XPath cont.

• Examples
• ////para elements para in the 4th level
• //chapter elements chapter anywhere in the
  document
• //bold //italic all elements bold a
  italic, anywehere in the document
• /book/chapter2 second chapter
• /book/chapterlast
• //chapter_at_id'k2'
• ../_at_lang attribute lang of the parent of
  current node
• //count(para)3 all element that contain
  exactly three elements para

7
Transformations of XML docs.

• motivation
• e.g. presenting the content of XML documents
  (users don't want to see the tags, they want the
  content to be nicely formatted...)?
• style (style sheet)?
• Relation between logical structure and
  presentation form
• XSL eXtensible Stylesheet Language
• Description of transformations of XML docs
• XSLT XSL Transformation
• Transforming process realized by an XSLT
  processor
• xsltproc test.xsl test.xml gt test.html

8
XSL

• Stylesheet declaration XML document, using xsl
  namespace
• ltxslstylesheet version"1.0" xmlnsxsl"http//ww
  w.w3.org/1999/XSL/Transform"gt
• declaration of templates ablon
• lt/xslstylesheetgt
• Style body at least one transformation rule
  (called template)?
• matching expression for finding nodes on which
  the template should be applied
• output found nodes will be substited by the
  specified output
• ltxsltemplate matchmatching_expressiongt
• output
• lt/xsltemplategt

9
XSL - Example
lt?xml version"1.0" encoding"utf-8"?gt ltxslstyles
heet version"1.0" xmlnsxsl"http//www.w3.org/19
99/XSL/Transform"gt ltxsltemplate match"/"gt
lthtmlgt ltheadgtlt/headgt ltbodygt
ltxslapply-templates/gt lt/bodygt
lt/htmlgt lt/xsltemplategt ltxsltemplate
match"title"gt lth1gt ltxslnumber/gt.
ltxslvalue-of select"."/gt (id
ltxslvalue-of select"../_at_id"/gt)? lt/h1gt
lt/xsltemplategt lt/xslstylesheetgt
ltbookgt ltchapter id"k1"gt lttitlegtIntro...lt/title
gt bla bla lt/chaptergt ltchapter id"k2"gt
lttitlegtConcl...lt/titlegt bla bla
lt/chaptergt lt/bookgt
10
Aplication interface for XML

• (API)?
• SAX Simple API for XML
• a document is read serially and its contents are
  reported as callbacks
• fast and efficient to implement, but user
  applications have to keep tract of what part of
  the document is being processed
• DOM Document Object Model
• allows for navigation of the entire document
  represented as a tree of objects
• language-neutral interface to an in-memory
  representation of an XML document

11
SAX Event Handlers in Perl

• Each type of event is processed by a procedure
  with a dedicated name

12
DOM

• The DOM presents an XML document as a
  tree-structure (a node tree), with the elements,
  attributes, and text defined as nodes.
• The entire document is a document node
• Every XML tag is an element node
• The texts contained in the XML elements are text
  nodes
• Every XML attribute is an attribute node
• Comments are comment nodes
• Example

13
DOM in Perl
ltknihagt ltkapitola id"k1"gt ltnazevgtUvodlt/nazevgt
bla bla lt/kapitolagt ltkapitola id"k2"gt
ltnazevgtZaverlt/nazevgt bla bla
lt/kapitolagt lt/knihagt

• XMLDOM nebo XMLLibXML
• Ukázka
• !/usr/bin/perl
• use XMLDOM
• my parser XMLDOMParser-gtnew()
• my doc parser-gtparsefile('test.xml')
• foreach my kap (doc-gtgetElementsByTagName('kapit
  ola'))
• print "Attribute id contains
  ".kap-gtgetAttribute("id")."\n"
• foreach child (kap-gtgetChildNodes)
• my type child-gtgetNodeType()
• if (type ELEMENT_NODE)
• print "Element ".child-gtgetTagName."
  contains ".
• child-gtgetFirstChild-gtgetNodeValue."\n"