XML. Part I XML Document and DTD

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1 XML Part I XML Document and DTD

2 What is XML? XML = Extensible Markup Language A Mark up language Designed based on SGML with less complexity Goal: data interchange over the web

3 What is XML? เป ด น อย HTML <html> <head><title>name</title></head> <body> <p>เป ด น อย</p> </body> </html> XML <name> <first>เป ด</first> <last>น อย</last> </name> Self-describing

4 XML is extensible Document Type Tags are freed to created Structures are freed to form Documents are created using Tags, structure and text XML Document that use to describe something is called document type The types of XML document created may vary based on their creator

5 Rules for elements Well-Formed XML Every start-tag must have a matching end-tag or be a self-closing tag Tag can t overlap; elements must be properly nested XML Documents can have only 1 root element Element names must obey XML naming conventions XML is case sensitive XML will keep whitespace in data

6 <p> </p Nested tag Some <strong> formatted <em> text </strong>, but </em> no grammar no good! <p> </p Some <strong> formatted <em> text </em> </strong> <em>, but </em> no grammar no good!

7 One root element <name>john</name> <name>jane</name> <names> <name>john</name> <name>jane</name> </names> <name></name>

8 XML Naming Convention Names can start with letters (including non-latin characters) or the dash (-) character, but not numbers or other punctuation characters After the first character, numbers, hyphens, and periods are allowed Names can t contain spaces Names can t contain the colon (:) character Names can t start with the letters xml, in uppercase, lowercase, or mixed There can t be a space after the opening < character

9 Example <first.name> <résumé> <xml-tag> <123> <fun=xml> <my tag> < this.tag>

10 Well-formed XML Attributes Attributes are simple name/value pair attached to the start-tag Attributes must have values even if it is an empty string Attribute s value must be in quote Attribute s naming must follow the same rule as naming element (tag) The elements cannot have attribute with the same name twice or more

11 Example <input checked> <input checked=true> <input checked= true > <input checked= checked= F > <input checked= true > <input checked= true > <input checked= tr e > <input checked= tr e > <input checked= >

12 Well-formed XML Comments

13 Well-formed XML Empty Elements Refers to elements with no data Can be represented in 2 way <tag></tag> <tag /> or <tag/> but <tag/ > or <tag / > are incorrect

14 Well-formed XML In Windows system, giving an ext of.xml In other system, how to indentify? XML Declarations Used to identify document as XML document type Start with <? and end with?> Must include version attribute Attributes: encoding and standalone are optional The version, encoding and standalone must be in that order version should be 1.0 or 1.1 Must be right at the beginning of the file

15 Examples <?xml version= 1.0 encoding= UTF-16 standalone= yes?> XML specification version 1.0 Character encoding of the document Specify that the document -Exists entirely on its own or -Depends on external DTD

16 Reserved characters < > & are reserved in XML To use reserved characters as data Use escaping characters & for &, < for <, > for >, ' for, " for &#yyy; yyy is the unicode number of the character in decimal (&#x yyy for number in hex) Use CDATA <![CDATA[6 is < 7 & 7 > 6]]>

17 XML Namespaces In real world application, there need to combine elements from various document type into one XML document With 2 or more document types, this may occurs: Elements/attributes with the same name but with different meaning XML namespace exists to solve the above problems XML namespace helps differentiate elements and attributes of different XML document types from each other when combining them together or processing multiple document simultaneously

18 Example 1 <?xml version= 1.0?> <person> <name> <title>sir</title> <first>john</first> <middle>fitzgerald Johansen</middle> <last>doe</last> </name> <position>vice President of Marketing</position> <resume> <html> <head><title>resume of John Doe</title></head> <body> <h1>john Doe</h1> <p>john s a great guy, you know?</p> </body> </html> </resume > </person>

19 Using prefixes The best way to solve this problem (same tag but different meaning) is to make tag to have a completely distinct name Adding prefixes to the tag names according to their document type

20 Example 2 <?xml version= 1.0?> <pers:person> <pers:name> <pers:title>sir</pers:title> <pers:first>john</pers:first> <pers:middle>fitzgerald Johansen</pers:middle> <pers:last>doe</pers:last> </pers:name> <pers:position>vice President of Marketing</pers:position> <pers:résumé> <xhtml:html> <xhtml:head><xhtml:title>resume of John Doe</xhtml:title></xhtml:head> <xhtml:body> <xhtml:h1>john Doe</xhtml:h1> <xhtml:p>john s a great guy, you know?</xhtml:p> </xhtml:body> </xhtml:html> </pers:résumé> </pers:person>

21 Using prefixes The drawback is that the names of XHTML element differ from standard XHTML names By using prefix, 2 kinds of elements are created in the document, e.g. any elements with prefix pers belong to the same group this groups are called namespace

23 Using prefixes Problem still exist if the authors choose the same prefix for their works Using unambiguous internet domain name as part of prefix will solve this problem

24 Example 3 <?xml version="1.0"?> <{ <{ <{ Sir </{  Even though it look like a URL, a namespace name is only used as a name, not a location

25 Using prefixes From Ex 3 the problem still exist, tag name contain forbidden character / { } To completely solve all the problem of namespace/prefix, three-part names are created 1 st part: attribute name 2 nd part: URI associated with the name for using as a namespace of the element 3 rd part: name according to naming rules choosen as prefix that refers to URI

26 Example 4: namespace declaration URI name <pers:person xmlns:pers=" 1 st 3 rd 2 nd <pers:person xmlns:pers=" <pers:name> <pers:title>sir</pers:title> </pers:name> </pers:person>

27 Example 5 <?xml version= 1.0?> <pers:person </pers:person> xmlns:pers= xmlns:html= > <pers:name> <pers:title>sir</pers:title> <pers:first>john</pers:first> <pers:middle>fitzgerald Johansen</pers:middle> <pers:last>doe</pers:last> </pers:name> <pers:position>vice President of Marketing</pers:position> <pers:résumé> <html:html> <html:head> <html:title>resume</html:title> </html:head> <html:body> <html:h1>john Doe</html:h1> <html:p>john s a great guy</html:p> </html:body> </html:html> </pers:résumé>

28 Default namespaces Making things about prefix easier XML code looks cleaner Example 6 <person xmlns=" <name> <title>sir</title> </name> </person>

29 Example 7 <person xmlns= xmlns:xhtml= > <name/> <xhtml:p>this is XHTML</xhtml:p> </person> <person xmlns= xmlns= >

30 Declaring Namespaces on Descendants Namespaces can be declared in: Root element Any element other than root By declaring namespace in root element the effect of declaration is global to the document Declaring namespace in other element the effect of declaration is local to that element and its child

31 Example 8 <person xmlns= > <name/> <xhtml:p xmlns:xhtml= > This is XHTML</xhtml:p> </person> <person xmlns= > <name/> <p xmlns= > This is XHTML</p> </person>

32 Canceling Default Namespace Default namespace can be cancel by setting xmlns attribute to null Example 9 <employee> <name>jane Doe</name> <notes> <p xmlns= >I ve worked with <name xmlns= >Jane Doe</name> for over a <em>year</em>now.</p> </notes> </employee>

33 Namespaces contain information (vocabulary) about Tags (element) only No information (vocabulary) about attributes kept inside namespace

34 Document Type Definition DTD helps validating XML documents Generally DTDs consist of 3 basic parts: Element declarations Attribute declarations Entity declarations To apply DTD to XML documents, document declaration: DOCTYPE must be declare

35 Declaring DTD Internal DTD Declaration DTD declared within the XML file <?xml version= 1.0 > <!DOCTYPE rootnode [ ]> <rootnode> </rootnode>

36 Declaring DTD External DTD Declaration DTD declared in a separate file <?xml version= 1.0 > <!DOCTYPE rootnode SYSTEM dtdfile.dtd > <rootnode> </rootnode>

37 Element Declarations Consist of 3 basic parts The ELEMENT declaration The element name The element content model Element, Mixed, Empty, Any <!ELEMENT name (first, middle, last)> Must appear in this order

38 Element content Sequences <!ELEMENT name (first, middle, last)> Choice <!ELEMENT location (address GPS)> Combining sequences and choice <!ELEMENT location (address (latitude, longitude))> Mixed content refers to any element with text in its content <!ELEMENT first (#PCDATA)> PCDATA: Parsed Character DATA text

39 <!ELEMENT description (#PCDATA em strong br)*> Using choice mechanism to describe content model In mixed content model #PCDATA must appear first in the list of choice * outside ( ) is known as a cardinality indicator, it tells the parser to repeat the content model With * the order or number of element are ignore Empty Content <!ELEMENT br EMPTY> Any Content As its name any elements declared within DTD can be use within the content in any order and any number of times <!ELEMENT description ANY>

40 Example 10 <name> <first>john</first> <middle>fitzgerald Johansen</middle> <last>doe</last> </name> <!ELEMENT name (first, middle, last)> <!ELEMENT first (#PCDATA)> <!ELEMENT middle (#PCDATA)> <!ELEMENT last (#PCDATA)>

41 Example 11 <location> <latitude> </latitude> <longitude> </longitude> </location> <location> <address>1 Chalongkrung Road</address> </location> <!ELEMENT location (address (latitude, longitude))> <!ELEMENT address (#PCDATA)> <!ELEMENT latitude (#PCDATA)> <!ELEMENT longitude (#PCDATA)>

42 Example 12 <description> The XML document<em>first edition</em><br/> We<strong> learn</strong> XML </description> <!ELEMENT description (#PCDATA em strong br)*> <!ELEMENT em (#PCDATA)> <!ELEMENT strong (#PCDATA)> <!ELEMENT br EMPTY>

43 Cardinality defines how many times the element will appear within a content model? the element may appear once or not at all + the element may appear one or more times * the element may appear zero or more times Example <!ELEMENT name (first+, middle?, last)> <!ELEMENT location (address* (latitude, longitude))> <!ELEMENT location (address* (latitude, longitude)*)>

44 <!ELEMENT name (first+, middle?, last)> <name> <first>john</first> <last>doe</last> </name> <name> <first>john</first> <first>fitzgerald</first> <last>doe</last> </name> <name> <first>john</first> <first>fitzgerald</first> <first>simon</first> <middle>johansen</middle> <last>doe</last> </name> <name> <first>john</first> <middle>johansen</middle> <last>doe</last> </name>

45 <!ELEMENT location (address* (latitude, longitude))> <!ELEMENT location (address* (latitude, longitude)*)> <location> <address>redlands, CA, USA</address> <latitude> </latitude> <longitude> </longitude> <latitude> </latitude> <longitude> </longitude> </location> <location> <address>redlands, CA, USA</address> <latitude> </latitude> <longitude> </longitude> </location>

46 <!ELEMENT location (address (latitude, longitude))*> <location> <latitude> </latitude> <longitude> </longitude> <address>redlands, CA, USA</address> <latitude> </latitude> <longitude> </longitude> </location>

W3C XML XML Overview

W3C XML XML Overview Overview Jaroslav Porubän 2008 References Tutorials, http://www.w3schools.com Specifications, World Wide Web Consortium, http://www.w3.org David Hunter, et al.: Beginning, 4th Edition, Wrox, 2007, 1080