Madalina Croitoru IUT Montpellier

Transcription

1 XML, DOM and the Web Madalina Croitoru IUT Montpellier

2 What is XML? Extensible Markup Language Markup Language (like HTML) Difference with HTML: HTML: designed to display data XML: designed to transport and carry data HTML: tags are already predefined XML: you define you own tags

3 XML does nothing XML was created to structure, store and transport information: <note> <to>tove</to> <from>jani</from> <heading>reminder</heading> <body>don't forget me this weekend! </body> </note>

4 XML and the Web Early Web: URI + HTTP +HTML URIs identify resources HTTP retrieves resources HTML is the resource format Web Today: many different technologies: URI+HTTP+HTML+PHP for basic Web publishing CSS & JavaScript for advanced publishing JavaScript & XML (AJAX) Scripts dynamically loading data from a server Machine-to-machine interaction: the server and the script

5 From Humans to Machines The Web was designed for humans: HTML is a language for describing page layouts and links Machines were only used for implementing it Search engines were the first machine users on the Web: They made the Web success possible They demonstrated how hard it is to understand HTML pages

6 HTML is for HUMANS HTML is: GOOD for rendering Web pages BAD for understanding Web pages Web growth in the late 90 s was enormous: Everybody putting information online which was inaccessible for machines

7 Machine-Friendly Web Information should be published in a machineunderstandable way: Machines need other structures to process Web content 1996: W3C Working Group SGML on the Web SGML a very complex and expensive technology HTML is just one document type defined with SGLM How can SGML be made easily and widely usable?

8 SGML, HTML and XML SGML: Standard Generalised Markup Language Language for designing document types HTML: Hypertext Markup Language Implements a simple SGML document type Its syntax is SGML but it uses very few SGML features XML: Extensible Markup Language A language for designing document types Greatly simplified version of SGML

9 XML usage for the Web Server side foundation for Web publishing Successful: Technically sound (simple) Human-readable based on a well-known syntax Great for rapid prototyping and experiments Ontologies etc.

10 XML Usage elsewhere Messages from sensors Genome sequences Scalable Vector Graphics Etc etc Information professionals should know and use XML: XML and some schema language XSLT for processing

11 XML is a syntax for trees Not all data is easily represented by trees XML encodes a structure purely on the syntactic level XML structures must be accompanied by XML structures must be accompanied by semantic descriptions

12 XML encoding XML documents can use a wide array of characters defined by Unicode Currently defines more than characters <?xml version= 1.0 encoding = UTF-8?> XML processors must support UTF-8 and UTF-16

13 Basic Concepts XML documents have an XML declaration Exactly one document element (the root element) Elements are marked up using tags Most elements have content, surrounded by start and end tags Elements may be nested Elements may be repeated Elements may have attributes

14 Example 1 <?xml version="1.0" encoding="iso "?> <note> <to>tove</to> <from>jani</from> <heading>reminder</heading> <body>don't forget me this weekend!</body> </note> root element: <note> 4 child elements of root: <to>, <from>, <heading>, and <body>

15 XML Documents form a Tree Structure <root> <child> <subchild>...</subchild> </child> </root>

16 Example 2 <bookstore> <book category="cooking"> <title lang="en">everyday Italian</title> <author>giada De Laurentiis</author> <year>2005</year> <price>30.00</price> </book> <book category="children"> <title lang="en">harry Potter</title> <author>j K. Rowling</author> <year>2005</year> <price>29.99</price> </book> <book category="web"> <title lang="en">learning XML</title> <author>erik T. Ray</author> <year>2003</year> <price>39.95</price> </book> </bookstore>

17 Syntax Rules All XML elements must have a closing tag XML tags are case sensitive XML elements must be properly nested XML Documents must have a root elements XML Attribute values must be quoted

18 Entity references and comments This will generate an XML error: <message>if salary < 1000 then</message> Use instead: <message>if salary < 1000 then</message>  Attention: with xml the white space in a document is preserved

19 XML attributes vs Elements <person sex="female"> <firstname>anna</firstname> <lastname>smith</lastname> </person> <person> <sex>female</sex> <firstname>anna</firstname> <lastname>smith</lastname> </person> As much as possible try to use elements rather than attributes

20 Why avoid XML attributes? Problems with using attributes: attributes cannot contain multiple values (elements can) attributes cannot contain tree structures (elements can) attributes are not easily expandable (for future changes)

21 Valid XML Documents A document which conforms to the rules for a Document Type Definition (DTD) <?xml version="1.0" encoding="iso "?> <!DOCTYPE note SYSTEM "Note.dtd"> <note> <to>tove</to> <from>jani</from> <heading>reminder</heading> <body>don't forget me this weekend!</body> </note>

22 XML DTD DOCTYPE is a reference to an external DTD file DTD file: defines the structure of an XML document <!DOCTYPE note [ <!ELEMENT note (to,from,heading,body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)> ]>

23 XML Schema W3C supports an XML-alternative to DTD called XML Schema: <xs:element name="note"> <xs:complextype> <xs:sequence> <xs:element name="to" type="xs:string"/> <xs:element name="from" type="xs:string"/> <xs:element name="heading" type="xs:string"/> <xs:element name="body" type="xs:string"/> </xs:sequence> </xs:complextype> </xs:element>

24 XML DTD <!DOCTYPE note [ <!ELEMENT note (to,from,heading,body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)> ]>!DOCTYPE note defines that the root element of this document is note!element note defines that the note element contains four elements: "to,from,heading,body"!element to defines the to element to be of type "#PCDATA"!ELEMENT from defines the from element to be of type "#PCDATA"!ELEMENT heading defines the heading element to be of type "#PCDATA"!ELEMENT body defines the body element to be of type "#PCDATA"

25 XML DTD External DTD declaration: <!DOCTYPE root-element SYSTEM "filename"> XML file: <?xml version="1.0"?> <!DOCTYPE note SYSTEM "note.dtd"> DTD file: <!ELEMENT >

26 DTD View: XML building blocks Elements Attributes extra information about elements. Come in name/value pairs Entities: &lt, &gt, &amp, &quot, &apos PCDATA: Parsed character data. The text that will be parsed by a parser for entities and markup CDATA: Character data. The text that will not be parsed by a parser (tags inside the text will not be treated as markup)

27 Declaring elements <!ELEMENT element-name category> or <!ELEMENT element-name (element-content)> <!ELEMENT element-name EMPTY> <!ELEMENT element-name (#PCDATA)> <!ELEMENT element-name (child1,child2,...)> <!ELEMENT note (message+)> <!ELEMENT note (message*)> <!ELEMENT note (to,from,header,(message body))>

28 Declaring attributes <!ATTLIST element-name attribute-name attribute-type default-value> <!ATTLIST payment type CDATA "check"> Attribute type: CDATA The value is character data (en1 en2..) The value must be one from an enumerated list ID The value is a unique id Default-value: #REQUIRED The attribute is required #IMPLIED The attribute is not required #FIXED value The attribute value is fixed

29 XML Schema defines elements that can appear in a document attributes that can appear in a document which elements are child elements the order of child elements the number of child elements whether an element is empty or can include text data types for elements and attributes default and fixed values for elements and attributes

30 XML, DTD, XML Schema <?xml version="1.0"?> <note> <to>tove</to> <from>jani</from> <heading>reminder</heading> <body>don't forget me this weekend!</body> </note> <!ELEMENT note (to, from, heading, body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)> <?xml version="1.0"?> <xs:schema xmlns:xs=" targetnamespace=" xmlns=" elementformdefault="qualified"> <xs:element name="note"> <xs:complextype> <xs:sequence> <xs:element name="to" type="xs:string"/> <xs:element name="from" type="xs:string"/> <xs:element name="heading" type="xs:string"/> <xs:element name="body" type="xs:string"/> </xs:sequence> </xs:complextype> </xs:element> </xs:schema>

31 Referencing an external XML Schema <?xml version="1.0"?> <note xmlns=" xmlns:xsi=" xsi:schemalocation=" note.xsd"> <to>tove</to>

32 The <schema> Element The root of every XML Schema <xs:schema> </xs:schema>

33 Simple Elements and Attributes <xs:element name="xxx" type="yyy"/> <xs:attribute name="xxx" type="yyy"/> xs:string xs:decimal xs:integer xs:boolean xs:date xs:time

34 Complex Elements <employee> <firstname>john</firstname> <lastname>smith</lastname> </employee> <xs:element name="employee"> <xs:element name="employee"> <xs:complextype> <xs:sequence> <xs:element name="firstname" type="xs:string"/> <xs:element name="lastname" type="xs:string"/> </xs:sequence> </xs:complextype> </xs:element>

35 DOM W3C standard Defines a standard for accessing documents like XML and HTML: Objects and properties of all document elements Methods to access them Three parts: Core DOM: standard model for any structured document XML DOM: standard model for XML documents HTML DOM: standard model for HTML documents

36 XML DOM Standard object model for XML Standard programming interface for XML A standard for how to get, change, add or delete XML elements: The entire document is a document node Every XML element is an element node The text in the XML elements are text nodes Every attribute is an attribute node Comments are comment nodes

37 XML DOM Node Tree XML DOM views an XML document as a tree-structure (called a node-tree)

38 Node Parents, Children, Siblings In a node tree, the top node is called the root Every node, except the root, has exactly one parent node A node can have any number of children A leaf is a node with no children Siblings are nodes with the same parent XML parser reads the XML, and converts it into an XML DOM object that can be accessed using different languages

39 The HTML DOM Node Tree

40 DOM Model? OK we have the model what do we do with it? Manipulate it with a programming language! In this lecture and practical lesson PHP Next week: JavaScript

41 DOM and PHP: the functions Let us consider the following XML file called note.xml: <?xml version="1.0" encoding="iso "?> <note> <to>tove</to> <from>jani</from> <heading>reminder</heading> <body>don't forget me this weekend!</body> </note>

42 Load and Output XML <?php $xmldoc = new DOMDocument(); //creates a DOMDocument-Object $xmldoc->load("note.xml"); // loads the XML print $xmldoc->savexml(); //puts the internal XML document into a string?> The output of this should be: Tove Jani Reminder Don't forget me this weekend!

43 Looping through XML <?php $xmldoc = new DOMDocument(); $xmldoc->load("note.xml"); $x = $xmldoc->documentelement; foreach ($x->childnodes AS $item) { print $item->nodename. " = ". $item->nodevalue. "<br />"; }?>

44 Other interesting functions getelementsbytagname(); $books = $doc->getelementsbytagname( "book" ); foreach( $books as $book ) { $authors = $book->getelementsbytagname( "author" ); $author = $authors->item(0)->nodevalue; } The script uses the getelementsbyname method to get a list of all of the elements with the given name. Within the loop of the book nodes, the script uses the getelementsbyname method to get the nodevalue for the author tags. The nodevalue is the text within the node.

45 More information (French) amiens.fr/mcr51:cours:dom#chargement_ d_un_fichier_xml_ou_d_une_chaine_xml_ php