XML Basics

1
XML Basics

• Overview

2
What is XML?

• Extensible Markup Language
• A syntax for documents
• A Meta-Markup Language
• A Structural and Semantic language, not a
  formatting language
• Not just for Web pages

3
XML is a Meta Markup Language

• Not like HTML, troff, LaTeX
• Make up the tags you needs as you need them
• The tags you create can be documented in a
  Document Type Definition (DTD)
• A meta syntax for domain-specific markup
  languages like MusicML, MathML, and CML

4
XML describes structure and semantics, not
formatting

• XML documents form a tree
• Element and attribute names reflect the kind of
  the element
• Formatting can be added with a style sheet

5
A Song Description in HTML

• ltdtgtHot Cop
• ltddgt by Jacques Morali, Henri Belolo, and Victor
  Willis
• ltulgt
• ltligtProducer Jacques Morali
• ltligtPublisher PolyGram Records
• ltligtLength 620
• ltligtWritten 1978
• ltligtArtist Village People
• lt/ulgt

6
A Song Description in XML

• ltSONGgt
• ltTITLEgtHot Coplt/TITLEgt
• ltCOMPOSERgtJacques Moralilt/COMPOSERgt
• ltCOMPOSERgtHenri Belololt/COMPOSERgt
• ltCOMPOSERgtVictor Willislt/COMPOSERgt
• ltPRODUCERgtJacques Moralilt/PRODUCERgt
• ltPUBLISHERgtPolyGram Recordslt/PUBLISHERgt
• ltLENGTHgt620lt/LENGTHgt
• ltYEARgt1978lt/YEARgt
• ltARTISTgtVillage Peoplelt/ARTISTgt
• lt/SONGgt

7
Style Sheets provide formatting

• SONG display block
• TITLE display block font-family Helvetica,
  serif
• font-size 20pt font-weight bold
• COMPOSER display block
• font-family Times, Times New Roman,
  serif
• font-size 14pt font-style italic
• ARTIST display block
• font-family Times, Times New Roman,
  serif
• font-size 14pt font-weight bold
• font-style italic
• PUBLISHER display block font-size 14pt
• font-family Times, Times New Roman,
  serif
• LENGTH display block
• font-family Times, Times New Roman,
  serif
• font-size 14pt
• YEAR display block
• font-family Times, Times New Roman,
  serif
• font-size 14pt

8
Attaching style sheets to documents

• Processing Instruction
• lt?xml-stylesheet type"text/css"
  href"song.css"?gt
• Converter Program

9
What is XML used for?

• Domain-Specific Markup Languages
• Self-Describing Data
• Interchange of Data Among Applications
• Structured and Integrated Data

10
Domain-Specific Markup Languages

• Non proprietary format
• Dont pay for what you dont use

11
Self-Describing Data

• Much data is lost due to format problems
• XML is very simple
• XML is self-describing
• XML is well documented

12

• ltPERSON ID"p1100" SEX"M"gt
• ltNAMEgt
• ltGIVENgtJudsonlt/GIVENgt
• ltSURNAMEgtMcDaniellt/SURNAMEgt
• lt/NAMEgt
• ltBIRTHgt
• ltDATEgt21 Feb 1834lt/DATEgt
• lt/BIRTHgt
• ltDEATHgt
• ltDATEgt9 Dec 1905lt/DATEgt
• lt/DEATHgt
• lt/PERSONgt

13
Interchange of Data Among Applications

• E-commerce
• Syndication

14
Structured and Integrated Data

• Can specify relationships between elements
• Can assemble data from multiple sources

15
XML Applications

• A specific markup language uses the XML
  meta-syntax is called an XML application
• Different XML applications have their own more
  constricted syntaxes and vocabularies within the
  broader XML syntax
• Further syntax can be layered on top of this
  e.g. data typing through DCDs or other schemas

16
Example XML Applications

• Web Pages
• Mathematical Equations
• Music Notation
• Vector Graphics
• Metadata
• and more

17
Mathematical Markup Language
18
Channel Definition Format
lt?xml version"1.0"?gt ltCHANNEL HREF"http//metala
b.unc.edu/xml/index.html"gt ltTITLEgtCafe con
Lechelt/TITLEgt ltITEM HREF"http//metalab.unc.edu
/xml/books.html"gt ltTITLEgtBooks about
XMLlt/TITLEgt lt/ITEMgt ltITEM HREF"http//metalab
.unc.edu/xml/tradeshows.html"gt ltTITLEgtTrade
shows and conferences about XMLlt/TITLEgt
lt/ITEMgt ltITEM HREF"http//metalab.unc.edu/xml/l
ists.htm"gt ltTITLEgtMailing Lists dedicated to
XMLlt/TITLEgt lt/ITEMgtlt/CHANNELgt
19
Classic Literature

• The Complete Plays of Shakespeare
• The Bible
• The Koran
• The Book of Mormon

20
Vector Graphics

• Vector Markup Language (VML)
• Internet Explorer 5.0
• Microsoft Office 2000
• Scalable Vector Graphics (SVG)

21
The Resource Description Framework (RDF)

• Meta-data
• Dublin Core
• Better Web searching

22
An Example of RDF

• ltrdfRDF
• xmlnsrdf"http//www.w3.org/1999/02/22-rdf-synta
  x-ns"
• xmlnsdc"http//purl.org/DC/gt
• ltrdfDescription about"http//metalab.unc.edu/x
  ml/gt
• ltdcCREATORgtElliotte Rusty Haroldlt/dcCREATORgt
  
• ltdcTITLEgtCafe con Lechelt/dcTITLEgt
• lt/rdfDescriptiongt
• lt/rdfRDFgt

23
XML for XML

• XSL The Extensible Stylesheet Language
• DCD The Document Content Description Schema
  Language
• XLL The Extensible Linking Language

24
XSL The Extensible Stylesheet Language

• XSL Transformations
• XSL Formatting Objects

25
DCD The Document Content Description Schema
Language

• Data Typing in XML is Weak
• ltMONTHgt9lt/MONTHgt
• ltDCDgt
• ltElementDef Type"MONTH"
• Model"Data" Datatype"i1"
• Min"1" Max"12" /gt
• lt/DCDgt

26
XLL The Extensible Linking Language

• Any element can be a link
• Links can be bi-directional
• Links can be separated from the documents they
  connect

ltfootnote xlinkform"simple" href"footnote7.xml"
gt7lt/footnotegt
27
File Formats, In-house applications, and other
behind the scenes uses

• Microsoft Office 2000
• Federal Express Web API
• Netscape Whats Related

28
Hello XML
lt?xml version"1.0" standalone"yes"?gt ltFOOgt Hello
XML! lt/FOOgt

• Plain ASCII or UTF-8 text
• .xml is standard file extension
• Any standard text editor will work

29
The XML Declaration
lt?xml version"1.0" standalone"yes"?gt

• version attribute
• required
• always has the value 1.0
• standalone attribute
• yes
• no
• encoding attribute
• UTF-8
• 8859_1
• etc.

30
The FOO element
ltFOOgt Hello XML! lt/FOOgt

• Start tag ltFOOgt
• Contents "Hello XML!"
• End tag lt/FOOgt

31
greeting.xml
lt?xml version"1.0" standalone"yes"?gt ltGREETINGgt
Hello XML! lt/GREETINGgt
32
Style sheets

• Separate from the XML document
• Different Languages
• Cascading Style Sheets Level 1 (CSS1)
• Internet Explorer 5.0
• Mozilla 5.0
• Cascading Style Sheets Level 2 (CSS2)
• Internet Explorer 5 (partial)
• Mozilla 5.0 (partial)
• Extensible Style Language (XSL)
• Internet Explorer 5.0 (older draft, buggy)
• LotusXSL, XT, Other non-browser converters
• Document Style and Semantics Language (DSSSL)
• Jade

33
xml-stylesheet

• Style sheets are attached via an xml-stylesheet
  processing instruction in the prolog
• lt?xml version"1.0" standalone"yes"?gt
• lt?xml-stylesheet type"text/css"
  href"greeting.css"?gt
• ltGREETINGgtHello XML!lt/GREETINGgt
• type attribute has the value text/css or text/xsl
• href attribute is a URL to the stylesheet,
  possibly relative
• Can also use non-browser converters like XT,
  LotusXSL, and Jade

34
greeting.css

• GREETING display block
• font-size 24pt
• font-weight bold

35
A larger example Baseball statistics

• Examine the data
• Design a vocabulary for the data
• Write a style sheet

36
Sample statistics

• http//cbs.sportsline.com/u/baseball/mlb/stats.htm

37
Organizing the Data

• XML documents are trees.
• XML elements contain other elements as well as
  text
• Within these limits there's more than one way to
  organize the data
• Hierarchically
• Relationally
• Objects

38
What is the Root Element

• The League?
• The Season?
• A custom Document element?

39
The Root Element

• Choose SEASON for the root element
• Everything else will be a descendant of SEASON
• This is not the only possible choice

lt?xml version"1.0"?gt ltSEASONgt lt/SEASONgt
40
What are the Immediate Children of The root?

• Leagues?
• Teams?
• Players?
• Games?

41
Child Elements

• lt?xml version"1.0"?gtltSEASONgt ltYEARgt 1998
  lt/YEARgtlt/SEASONgt

42
White space in XML is not especially significant

• lt?xml version"1.0"?gt
• ltSEASONgtltYEARgt1998lt/YEARgtlt/SEASONgt

43
Leagues

• Major league baseball is divided into two leagues
• Each league has
• a name
• three divisions

44
Divisions

• Each division has
• name
• 4-6 teams

45
Teams

• Each team has
• Name
• City
• Players

46
Player Data

• Each player has
• First name
• Last name
• Position
• Statistics

47
Player Batting Statistics

• SB Stolen Bases
• CS Caught Stealing
• SH Sacrifice Hits
• SF Sacrifice Flies
• Err Errors
• PB Pitcher Balked
• BB Base on Balls (Walks)
• SO Strike Outs
• HBP Hit By Pitch

• G Games Played
• GS Games Started
• AB At Bats
• R Runs
• H Hits
• 2B Doubles
• 3B Triples
• HR Home Runs
• RBI Runs Batted In

48
What does a player look like

• Long names vs. short names

49
The Complete 1998 Major League

• Long version

50
A Style Sheet

• 1998shortstats.xml
• baseballstats.css
• lt?xml-stylesheet type"text/css"
  href"baseballstats.css"?gt
• styled1998shortstats.xml

51
Cascading Style Sheets

• Partially supported by Mozilla and IE 5.0
• Full W3C Recommendation

52
The Default Rule

• Not every element needs a rule
• The root element should be at least display
  block
• SEASON font-size 14pt
• background-color white
• color black
• display block

53
A style rule for the YEAR element

• Make it look like a title
• YEAR display block
• font-size 32pt
• font-weight bold
• text-align center

54
Style Rules for Division and League Names

• LEAGUE_NAME display block
  text-align center font-size
  28pt font-weight bold
• DIVISION_NAME display block
  text-align center font-size
  24pt font-weight bold

55
Alternate Style Rules for Division and League
Names

• LEAGUE_NAME, DIVISION_NAME display block
  text-align center font-weight
  boldLEAGUE_NAME font-size 28pt
  DIVISION_NAME font-size 24pt

56
Style Rules for Teams

• Team name and Team city must be one title
• Must be inline elements
• Previous and following must be block elements
• TEAM_CITY font-size 20pt font-weight bold
  font-style italic
• TEAM_NAME font-size 20pt font-weight bold
  font-style italic
• TEAM, PLAYER display block

57
Style Rules for Players
TEAM display table TEAM_CITY display
table-caption TEAM_NAME display
table-caption PLAYER display
table-row SURNAME, GIVEN_NAME, POSITION,
GAMES, GAMES_STARTED, AT_BATS, RUNS, HITS,
DOUBLES, TRIPLES, HOME_RUNS, RBI,
STEALS, CAUGHT_STEALING, SACRIFICE_HITS,
SACRIFICE_FLIES, ERRORS, WALKS, STRUCK_OUT,
HIT_BY_PITCH display table-cell
58
Finished Style Sheet

• SEASON font-size 14pt background-color white
  color black display block
• YEAR display block font-size 32pt
• font-weight bold text-align center
• LEAGUE_NAME display block text-align center
  font-size 28pt font-weight bold
• DIVISION_NAME display block text-align
  center font-size 24pt font-weight bold
• TEAM_CITY font-size 20pt font-weight bold
  font-style italic
• TEAM_NAME font-size 20pt
• font-weight bold font-style italic
• TEAM display block
• PLAYER display block

59
Possible Extensions

• There should be captions like "RBI" or "At Bats.
• Derived numbers like batting averages are not
  included.
• The titles are short. E.g. "1998" instead of
  "1998 Major League Baseball".
• The document is so long it's hard to read.
  Something similar to IE5's collapsible outline
  view would be nice.
• Pitcher stats should be separated from batter
  stats.

60
Possible Solutions

• CSS Level 2
• XSL
• XSL JavaScript

61
Well-formedness Rules

• Open and close all tags
• Empty tags end with /gt
• There is a unique root element
• Elements may not overlap
• Attribute values are quoted
• lt and are only used to start tags and entities
• Only the five predefined entity references are
  used

62
Open and close all tags
63
Empty tags end with /gt

• ltBR/gt, ltHR/gt, and ltIMG/gt instead of ltBRgt, ltHRgt,
  and ltIMGgt
• Web browsers deal inconsistently with these
• Can use ltBRgtlt/BRgt ltHRgtlt/HRgt ltIMGgtlt/IMGgt instead

64
There is a unique root element

• One element completely contains all other
  elements of the document
• This is HTML in HTML files
• XML Declaration is not an element

lt?xml version"1.0" standalone"yes"?gt ltGREETINGgt
Hello XML! lt/GREETINGgt
65
Elements may not overlap

• If an element contains a start tag for an
  element, it must also contain the corresponding
  end tag
• Empty elements may appear anywhere
• Every non root element has a parent element

66
Attribute values are quoted

• Good
• ltA HREF"http//metalab.unc.edu/xml/"gt
• Bad
• ltA HREFhttp//metalab.unc.edu/xml/gt

67
lt and are only used to start tags and entities

• Good ltH1gtO'Reilly amp Associateslt/H1gt
• Bad ltH1gt O'Reilly Associateslt/H1gt
• Good
• ltCODEgtfor (int i 0 i lt args.length i )
  lt/CODEgt
• Bad
• ltCODEgtfor (int i 0 i lt args.length i )
  lt/CODEgt

68
Only the five predefined entity references are
used

• Good
• amp
• lt
• gt
• quot
• apos

• Bad
• copy
• reg
• tm
• alpha
• eacute
• nbsp
• etc.

69
DTDs and Validity

• A Document Type Definition describes the elements
  and attributes that may appear in a document
• Validation compares a particular document against
  a DTD
• Well-formedness is a prerequisite for validity

70
What is a DTD?

• a list of the elements, tags, attributes, and
  entities contained in a document, and their
  relationship to each other
• internal vs. external DTDs

71
The importance of validation

• Ensures that data is correct before feeding it
  into a program
• Ensure that a format is followed
• Establish what must be supported
• Not all documents need to be valid sometimes
  well-formed is enough

72
A DTD for greeting.xml

• greeting.xml
• lt?xml version"1.0"?gt
• ltGREETINGgt
• Hello XML!
• lt/GREETINGgt
• greeting.dtd
• lt!ELEMENT GREETING (PCDATA)gt

73
Document Type Declarations

• lt?xml version"1.0"?gt
• lt!DOCTYPE GREETING SYSTEM "greeting.dtd"gt
• ltGREETINGgt
• Hello XML!
• lt/GREETINGgt
• specifies the root element
• gives a URL for the DTD

74
Invalid Documents

• Valid
• ltGREETINGgt
• various random text but no markup
• lt/GREETINGgt
• Invalid anything else including
• ltGREETINGgt
• ltsometaggtvarious random textlt/sometaggt
• ltsomeEmptyTag/gt
• lt/GREETINGgt
• or
• ltGREETINGgt
• ltGREETINGgtvarious random textlt/GREETINGgt
• lt/GREETINGgt

75
Validating Tools

• Command line programs like XJParse
• Online validators
• http//www.stg.brown.edu/service/xmlvalid/
• http//www.cogsci.ed.ac.uk/7Erichard/xml-check.ht
  ml
• Browsers

76
Element Declarations

• Each tag must be declared in a lt!ELEMENTgt
  declaration.
• A lt!ELEMENTgt declaration gives the name and
  content model of the element
• The content model uses a simple regular
  expression-like grammar to precisely specify what
  is and isn't allowed in an element

77
Content Specifications

• ANY
• PCDATA
• Sequences
• Choices
• Mixed Content
• Modifiers
• Empty

78
ANY

• lt!ELEMENT SEASON ANYgt
• A SEASON can contain any child element and/or raw
  text (parsed character data)

79
PCDATA

• lt!ELEMENT YEAR (PCDATA)gt
• Parsed Character Data i.e. raw text, no markup

80
PCDATA

• Invalid
• ltYEARgt
• ltMONTHgtJanuarylt/MONTHgt
• ltMONTHgtFebruarylt/MONTHgt
• ltMONTHgtMarchlt/MONTHgt
• ltMONTHgtAprillt/MONTHgt
• ltMONTHgtMaylt/MONTHgt
• ltMONTHgtJunelt/MONTHgt
• ltMONTHgtJulylt/MONTHgt
• ltMONTHgtAugustlt/MONTHgt
• ltMONTHgtSeptemberlt/MONTHgt
• ltMONTHgtOctoberlt/MONTHgt
• ltMONTHgtNovemberlt/MONTHgt
• ltMONTHgtDecemberlt/MONTHgt
• lt/YEARgt

• Valid
• ltYEARgt1999lt/YEARgt
• ltYEARgt99lt/YEARgt
• ltYEARgt1999 C.E.lt/YEARgt
• ltYEARgt
• The year of our Lord one thousand, nine hundred,
  and ninety-nine
• lt/YEARgt

81
Child Elements

• To declare that a LEAGUE element must have a
  LEAGUE_NAME child
• lt!ELEMENT LEAGUE (LEAGUE_NAME)gt
• lt!ELEMENT LEAGUE_NAME (PCDATA)gt

82
Sequences

• Separate multiple required child elements with
  commas e.g.
• lt!ELEMENT SEASON (YEAR, LEAGUE, LEAGUE)gt
• lt!ELEMENT LEAGUE (LEAGUE_NAME, DIVISION,
  DIVISION, DIVISION)gt

83
One or More Children

• lt!ELEMENT DIVISION_NAME (PCDATA)gt
• lt!ELEMENT DIVISION (DIVISION_NAME, TEAM)gt

84
Zero or More Children

• lt!ELEMENT TEAM (TEAM_CITY, TEAM_NAME, PLAYER)gt
• lt!ELEMENT TEAM_CITY (PCDATA)gt
• lt!ELEMENT TEAM_NAME (PCDATA)gt

85
Zero or One Children ?

• lt!ELEMENT PLAYER (GIVEN_NAME, SURNAME, POSITION,
  GAMES, GAMES_STARTED, AT_BATS?, RUNS?, HITS?,
  DOUBLES?, TRIPLES?, HOME_RUNS?, RBI?, STEALS?,
  CAUGHT_STEALING?, SACRIFICE_HITS?,
  SACRIFICE_FLIES?, ERRORS?, WALKS?, STRUCK_OUT?,
  HIT_BY_PITCH?, WINS?, LOSSES?, SAVES?,
  COMPLETE_GAMES?, SHUT_OUTS?, ERA?, INNINGS?,
  EARNED_RUNS?, HIT_BATTER?, WILD_PITCHES?,
  BALK?,WALKED_BATTER?, STRUCK_OUT_BATTER?)
• gt

86
Finished DTD
87
Choices

• lt!ELEMENT PAYMENT (CASH CREDIT_CARD)gt
• lt!ELEMENT PAYMENT (CASH CREDIT_CARD CHECK)gt

88
Grouping With Parentheses

• Parentheses combine several elements into a
  single element.
• Parenthesized element can be nested inside other
  parentheses in place of a single element.
• The parenthesized element can be suffixed with a
  plus sign, a comma, or a question mark.
• lt!ELEMENT dl (dt, dd)gt
• lt!ELEMENT ARTICLE (TITLE, (P PHOTO GRAPH
  SIDEBAR PULLQUOTE SUBHEAD), BYLINE?)gt

89
Mixed Content

• Both PCDATA and child elements in a choice
• lt!ELEMENT TEAM (PCDATA TEAM_CITY TEAM_NAME
  PLAYER)gt
• PCDATA must come first
• PCDATA cannot be used in a sequence

90
Empty elements

• lt!ELEMENT BR EMPTYgt
• lt!ELEMENT IMG EMPTYgt
• lt!ELEMENT HR EMPTYgt

91
Internal DTDs

• lt?xml version"1.0"?gt
• lt!DOCTYPE GREETING
• lt!ELEMENT GREETING (PCDATA)gt
• gt
• ltGREETINGgt
• Hello XML!
• lt/GREETINGgt

92
Internal DTD Subsets

• lt?xml version"1.0"?gt
• lt!DOCTYPE GREETING SYSTEM "greeting.dtd"
• lt!ELEMENT GREETING (PCDATA)gt
• gt
• ltGREETINGgt
• Hello XML!
• lt/GREETINGgt
• Internal declarations override external
  declarations

93
Programming with XML

• Java works best
• C, Perl, Python etc. can also be used
• Unicode support is the biggest issue

94
SAX, the Simple API for XML

• Event based
• Programs can plug in different parsers

95
The Document Object Model (DOM)
96
To Learn More Books

• XML Extensible Markup Language
• IDG Books 1998
• ISBN 0-76453-199-9
• The XML Bible
• IDG Books 1999
• ISBN 0-76453-236-7

97
Questions?