XML

1
XML

• An introduction

2
xml

• XML like HTML is created from the Standard
  Generalized Markup Language, SGML

3
A brief introduction to XML A simple xml doc

• lt?xml version 1.0?gt
• lt! a simple xml examplethis is a comment --!gt
• ltmymessagegt
• ltmessagegtWelcome to XML!lt/messagegt
• lt/mymessagegt

4
In validator file is in examples\ch05\intro.xml
5
XML documents and format

• An XML document contains data, not formatting
  information. As well learn, there are ways (xsl
  and fo files, for example) to provide formatting
  for xml analogous to that in which css provided
  formatting for html.

6
XML

• XML are typically stored in a file with suffix
  .xml, though this is not required. They can be
  created with any editor (save as ASCII text).
  Many packages like MS Word can save files as type
  .xml
• An xml document contains a single root which
  contains other elements, Anything appearing
  before the root is called the prolog. Elements
  directly under the root are its children. The
  structure is recursive.
• In the example, the roots child message contains
  the text Here is some message.

7
The character set

• XML characters are CR, LF and Unicode.
• An XML document consists of markup and character
  data.
• Markup is enclosed in angle brackets (like html)
  ltgt
• Character data appears between the start and end
  tag.
• An xml parser passes whitespace characters to the
  application. Insignificant whitespace can be
  collapsed in a process called normalization.
• It is a good idea to add whitespace to an xml
  document for readability.
• , lt, gt, and are reserved characters. An
  entity reference makes it possible to use these
  as characters in the character data part of an
  xml document.
• Entity references begin with and end with
• In this way character data is not confused with
  markup.
• Single and double quote are used to delimit
  attribute values.

8
More on syntax

• There must be exactly one root.
• Proper nesting of elements is required.
• Start tags require close tags.
• Unlike HTML, the author can define her own tags
  in XML.
• Tags are case sensitive
• Parser needs to distinguish markup from character
  data
• Typically, whitespace is normalized reduced to
  1 whitespace char.
• Entity references are marked with an ampersand
  and allow us to use meta characters (lt, gt and
  so on) which are part of the language syntax.
• Entity references (for example, lt) allow us
  to represent and distinguish the reserved
  characters lt,gt, in XML.
• They may only appear as an entity reference in
  character data

9
XML intro continued

• A DOM-based parser returns a tree structure. A
  DOM parser must process the entire document to
  create a (java) object which may be 3 or 4X the
  size of the original. Not advisable if there are
  storage size constraints.
• A SAX (Simple-API for XML) -based parser returns
  events. SAX parsers have a smaller footprint.
• Many parsers can be downloaded for free and
  several come with java 1.4

10
A brief introduction to XML

• An xml validator parses an XML document and
  indicates if it is correct.
• A number of free Validators are available,
  including one from MS which I downloaded and used
  in this ppt.

11
Validator

• Microsoft provides a validating program free for
  download (with javascript and VBscript versions)
  at
• http//msdn.microsoft.com/archive/default.asp?url
  /archive/en-us/samples/internet/xml/xml_validator/
  default.asp
• Or search MSDNvalidator
• There are others out there
• http//validator.w3.org/
• http//www.stg.brown.edu/service/xmlvalid/
• http//www.w3schools.com/XML/xml_validator.asp

12
Link to validator program on my w drive

• http//employees.oneonta.edu/higgindm/internet20p
  rogramming/validate_js.htm
• This is a link for javascript validator
• http//employees.oneonta.edu/higgindm/internet20p
  rogramming/validate_vbs.htm
• This is a link for vbscript validator

13
MS Validatorhttp//employees.oneonta.edu/higgind
m/internet20programming/validate_js.htm
14
Parser continued

• The parser will indicate if the document is
  well-formed.
• In DOM-based parsing, a in the left margin
  indicates a node has children and a indicates
  all child nodes have been expanded.
• The MS Validator uses color coding to indicate
  child nodes can be expanded
• An element that stores other elements is called a
  container element.
• The parser makes the document content available
  for further processing if it is well-formed.

15
Validator example
16
Validator
17
Reserved characters

• ltmessagegtltgtamplt/messagegt would enable a
  character data message to contain characters ltgt

18
DTD document type definition

• a dtd file may contain the definition of an xml
  structure.
• XML files may refer back to a dtd.
• If an XML document has a DTD or Schema, a
  validating parser can determine not merely if it
  is well-formed XML, but whether it is valid.
• Valid means conforming to a dtd or schema.

19
Another example Unicode

• Lang.xml (next slide) uses unicode entity
  references to represent arabic words.
• lang.dtd (also shown in a later slide) is used to
  generate unicode characters (arabic) for some
  entity references in the XML file.

20
DTD document type definition a dtd file may
contain the definition of an xml structure.

• lt?xml version "1.0"?gt
• lt!-- Fig. 5.4 lang.xml --gt
• lt!-- Demonstrating Unicode --gt
• lt!DOCTYPE welcome SYSTEM "lang.dtd"gt
• ltwelcomegt
• ltfromgt
• lt!-- Deitel and Associates --gt
• 158315751610157816141604
• 157116061583
• lt!-- entity --gt
• assoc
• lt/fromgt
• ltsubjectgt
• lt!-- Welcome to the world of Unicode --gt
• 15711607160415751611
• 157616031605
• 160116101616
• 1593157516041605
• lt!-- entity --gt

21
Lang.dtd

• lt!-- lang.dtd --gt
• lt!ELEMENT welcome ( from, subject )gt
• lt!ELEMENT from ( PCDATA )gt
• lt!ELEMENT subject ( PCDATA )gt
• lt!ENTITY assoc "15711587161716081588
  161616101614157816181587"gt
• lt!ENTITY text "15751604161016081606
  1610160316081583"gt

22
Lang.xml in validator
23
Lang.xml in IE
24
About the example

• The DTD reference contains DOCTYPE, the name of
  the root, the SYSTEM flag indicating the DTD file
  is external, and the name of that file.
• Root element welcome contains two elements from
  and subject.
• Some lines contain entity references for unicode.
• The DTD also defines some other entity references.

25
More about markup

• XML end tags may consist of /gt if there is an
  empty element as in
• ltemptyelt xxxx /gt
• but otherwise must consist of a complete end-tag
  as in
• ltsometaggt xxxxxxxxxxx lt/sometaggt
• Elements may or may not have content (child
  elements or character data)
• Elements may have 0 or more attributes associated
  with them. Attributes appear in the elements
  start tag
• ltcar doors 4/gt
• Attribute values must appear in single or double
  quotes.
• Element and attribute names may not contain
  blanks.
• Here, element car has attribute doors with value
  4.
• Attributes may contain any characters and be of
  any length but must start with a letter or
  underscore.

26
Usage.xml uses a stylesheet

• lt?xml version "1.0"?gt
• lt!-- Fig. 5.5 usage.xml --gt
• lt!-- Usage of elements and attributes --gt
• lt?xmlstylesheet type "text/xsl" href
  "usage.xsl"?gt
• ltbook isbn "999-99999-9-X"gt
• lttitlegtDeitelaposs XML Primerlt/titlegt
• ltauthorgt
• ltfirstNamegtPaullt/firstNamegt
• ltlastNamegtDeitellt/lastNamegt
• lt/authorgt
• ltchaptersgt
• ltpreface num "1" pages
  "2"gtWelcomelt/prefacegt
• ltchapter num "1" pages "4"gtEasy
  XMLlt/chaptergt
• ltchapter num "2" pages "2"gtXML
  Elements?lt/chaptergt

27
Usage.xls

• In notes
• lt? Xxxxx ?gt in usage.xml represents a pi (that
  is, a processing instruction). PI consist of a
  PI target (xmlstylesheet, in this example) and a
  PI value. Note syntax.
• PI can be used to help authors embed
  application-specific data in an xml document. If
  the application processing the xml doesnt use
  the PI, then it has no effect on the xml document
  content.

28
Usage.xml in validator
29
Usage.XML document loaded into IE Browser uses
stylesheet to generate HTML
30
CData

• The character data appearing in CData sections is
  ignored by the xml parser.
• CData might be used for JavaScript or VBScript.
• CData starts with lt!CData and ends with gt
• CData may contain reserved characters, but not
  the text gt

31
Text example 5.7

• lt?xml version "1.0"?gt
• lt!-- Fig. 5.7 cdata.xml --gt
• lt!-- CDATA section containing C code --gt
• ltbook title "C How to Program" edition "3"gt
• ltsamplegt
• // C comment
• if ( this-gtgetX() lt 5 ampamp
  value 0 ! 3 )
• cerr ltlt this-gtdisplayError()
  
• lt/samplegt
• ltsamplegt
• lt!CDATA
• // C comment
• if ( this-gtgetX() lt 5 value 0 ! 3
  )
• cerr ltlt this-gtdisplayError()
• gt
• lt/samplegt
• C How to Program by Deitel amp Deitel
• lt/bookgt

32
CData example from text 5.7
33
Cdata.xml in MS validator (file is in
examples\ch05)
34
letter.xml - I removed blank lines to get it to
fit here

• lt?xml version "1.0"?gt
• ltlettergt
• ltcontact type "from"gt
• ltnamegtJane Doelt/namegt
• ltaddress1gtBox 12345lt/address1gt
• ltaddress2gt15 Any Ave.lt/address2gt
• ltcitygtOthertownlt/citygt
• ltstategtOtherstatelt/stategt
• ltzipgt67890lt/zipgt
• ltphonegt555-4321lt/phonegt
• ltflag gender "F"/gt
• lt/contactgt
• ltcontact type "to"gt
• ltnamegtJohn Doelt/namegt
• ltaddress1gt123 Main St.lt/address1gt
• ltaddress2gtlt/address2gt
• ltcitygtAnytownlt/citygt
• ltstategtAnystatelt/stategt
• ltzipgt12345lt/zipgt

35
letter.xml in Validator
36
namespaces

• Naming collisions can occur when xml authors use
  the same tag names
• Namespaces provide a mechanism for making tag
  references unambiguous.
• A namespace reference appears with the start and
  end tags followed by a colon. So,
• ltmoviecharactergtScroogelt/moviecharactergt can be
  differentiated from ltasciicharactergtcolonlt/ascii
  charactergt
• Namespace prefixes are tied to unique URI in the
  xml document. Almost any name can be used to
  create a namespace prefix.
• In this example ascii and movie are namespace
  prefixes. Namespace prefixes can precede element
  and attribute values to avoid collisions.
• A URL may be used for a URI. The only
  requirement though is uniqueness as the URLs are
  not visited by the parser.

37
Namespace example 5.8

• lt?xml version "1.0"?gt
• lt!-- Fig. 5.8 namespace.xml --gt
• lt!-- Namespaces --gt
• lttextdirectory xmlnstext "urndeiteltextInfo"
  
• xmlnsimage "urndeitelimageInfo"gt
• lttextfile filename "book.xml"gt
• lttextdescriptiongtA book listlt/textdescript
  iongt
• lt/textfilegt
• ltimagefile filename "funny.jpg"gt
• ltimagedescriptiongtA funny
  picturelt/imagedescriptiongt
• ltimagesize width "200" height "100"/gt
• lt/imagefilegt
• lt/textdirectorygt

38
Namespace.xml in validator file is in
examples\ch05
39
Namespace.xml example 5.8 in IE
40
Namespaces continued

• Providing a prefix can be tedious. A default
  namespace can be created and elements and
  attributes used in the xml document from this
  namespace do not need prefixes.

41
Default namespaces

• lt?xml version "1.0"?gt
• lt!-- Fig. 5.9 defaultnamespace.xml --gt
• lt!-- Using Default Namespaces --gt
• ltdirectory xmlns "urndeiteltextInfo"
• xmlnsimage "urndeitelimageInfo"gt
• ltfile filename "book.xml"gt
• ltdescriptiongtA book listlt/descriptiongt
• lt/filegt
• ltimagefile filename "funny.jpg"gt
• ltimagedescriptiongtA funny
  picturelt/imagedescriptiongt
• ltimagesize width "200" height "100"/gt
• lt/imagefilegt
• lt/directorygt

42
Default namespaces

• Now, file is in the default namespace.
• Compare this example to the earlier namespace
  example where text and image were distinct
  namespaces.

43
Defaultnamespace.xml in IE
44
Day planner case studyto be continued

• lt?xml version "1.0"?gt
• lt!-- Fig. 5.10 planner.xml --gt
• lt!-- Day Planner XML document --gt
• ltplannergt
• ltyear value "2000"gt
• ltdate month "7" day "15"gt
• ltnote time "1430"gtDoctoraposs
  appointmentlt/notegt
• ltnote time "1620"gtPhysics class at
  BH291Clt/notegt
• lt/dategt
• ltdate month "7" day "4"gt
• ltnotegtIndependence Daylt/notegt
• lt/dategt
• ltdate month "7" day "20"gt
• ltnote time "0900"gtGeneral Meeting in
  room 32-Alt/notegt
• lt/dategt
• ltdate month "7" day "20"gt
• ltnote time "1900"gtParty at
  Joeaposslt/notegt
• lt/dategt
• ltdate month "7" day "20"gt

45
Planner.xml in validator
46
day planner using a java GUI. SAX parser is used
to parse the document.(in text chapter 8)
47
Homework on this section

• Install an xml validator
• Create your own xml file and validate it.
• Post screenshots of your XML file and what
  validator.