x Ml Basics Seminar

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XML Basics

Wednesday May 12, 1999 SD99

Copyright 1999 Elliotte Rusty Harold

[email protected]

http://metalab.unc.edu/xml/slides/



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



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 bedocumented in a Document Type

Definition (DTD)

• A meta syntax for domain-specificmarkup languages like MusicML,

MathML, and CML



XML describes structure andsemantics, not formatting

• XML documents form a tree

• Element and attribute names reflect

the kind of the element

• Formatting can be added with a stylesheet



A Song Description in HTML

<dt>Hot Cop <dd> by Jacques Morali, Henri

Belolo, and Victor Willis <ul> <li>Producer: Jacques Morali <li>Publisher: PolyGram Records <li>Length: 6:20

<li>Written: 1978 <li>Artist: Village People </ul>

http://examples/hotcop.html



A Song Description in XML

<SONG> <TITLE>Hot Cop</TITLE> <COMPOSER>Jacques Morali</COMPOSER>

<COMPOSER>Henri Belolo</COMPOSER> <COMPOSER>Victor Willis</COMPOSER> <PRODUCER>Jacques Morali</PRODUCER> <PUBLISHER>PolyGram Records</PUBLISHER>

<LENGTH>6:20</LENGTH> <YEAR>1978</YEAR> <ARTIST>Village People</ARTIST>

</SONG>

http://examples/hotcop.xml



Style Sheets provide formattingSONG {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}

http://examples/csshotcop.xml



Attaching style sheets todocuments

• Processing Instruction

<?xml-stylesheet type="text/css"href="song.css"?>

• Converter Program



What is XML used for?

• Domain-Specific Markup Languages

• Self-Describing Data

• Interchange of Data Among Applications

•

Structured and Integrated Data



Domain-Specific MarkupLanguages

• Non proprietary format

• Don’t pay for what you don’t use



Self-Describing Data

• Much data is lost due to formatproblems

• XML is very simple

• XML is self-describing

•

XML is well documented



<PERSON ID="p1100" SEX="M"> <NAME> <GIVEN>Judson</GIVEN>

<SURNAME>McDaniel</SURNAME> </NAME> <BIRTH> <DATE>21 Feb 1834</DATE>

</BIRTH> <DEATH> <DATE>9 Dec 1905</DATE>

</DEATH>

</PERSON>



Interchange of Data Among Applications

• E-commerce

• Syndication



Structured and Integrated Data

• Can specify relationships betweenelements

• Can assemble data from multiplesources



XML Applications

• A specific markup language uses the XML meta-syntax is called an XMLapplication

• Different XML applications havetheir own more constricted syntaxesand vocabularies within the broader

XML syntax

• Further syntax can be layered ontop of this; e.g. data typing through

DCDs or other schemas



Example XML Applications

• Web Pages

• Mathematical Equations

• Music Notation

• Vector Graphics

• Metadata

• and more…



Mathematical Markup Language



Channel Definition Format

<?xml version="1.0"?> <CHANNEL HREF="http://metalab.unc.edu/xml/index.html"> <TITLE>Cafe con Leche</TITLE> <ITEM HREF="http://metalab.unc.edu/xml/books.html"> <TITLE>Books about XML</TITLE>

</ITEM> <ITEM HREF="http://metalab.unc.edu/xml/tradeshows.html"> <TITLE>Trade shows and conferences about XML</TITLE>

</ITEM> <ITEM HREF="http://metalab.unc.edu/xml/lists.htm"> <TITLE>Mailing Lists dedicated to XML</TITLE>

</ITEM> </CHANNEL>



Classic Literature

• The Complete Plays of Shakespeare

• The Bible

• The Koran

• The Book of Mormon



Vector Graphics

• Vector Markup Language (VML)

– Internet Explorer 5.0

– Microsoft Office 2000

• Scalable Vector Graphics (SVG)

http://examples/22-7.html



The Resource Description

Framework (RDF)

• Meta-data

• Dublin Core

• Better Web searching



An Example of RDF

<rdf:RDFxmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:dc="http://purl.org/DC/> <rdf:Descriptionabout="http://metalab.unc.edu/xml/> <dc:CREATOR>Elliotte Rusty

Harold</dc:CREATOR>

<dc:TITLE>Cafe con Leche</dc:TITLE> </rdf:Description>

</rdf:RDF>



XML for XML

• XSL: The Extensible StylesheetLanguage

• DCD: The Document ContentDescription Schema Language

• XLL: The Extensible Linking Language



XSL: The Extensible StylesheetLanguage

• XSL Transformations

• XSL Formatting Objects



DCD: The Document ContentDescription Schema Language

• Data Typing in XML is Weak

• <MONTH>9</MONTH>

<DCD> <ElementDef Type="MONTH"

Model="Data" Datatype="i1" Min="1" Max="12" />

</DCD>



XLL: The Extensible LinkingLanguage

• Any element can be a link

• Links can be bi-directional

• Links can be separated from thedocuments they connect

<footnote xlink:form="simple"href="footnote7.xml">7</footnote>

File Formats In house



File Formats, In-houseapplications, and other behind

the scenes uses • Microsoft Office 2000

• Federal Express Web API

• Netscape What’s Related



Hello XML

<?xml version="1.0" standalone="yes"?> <FOO> Hello XML!

</FOO>

• Plain ASCII or UTF-8 text

• .xml is standard file extension

• Any standard text editor will work

http://hello.xml/

http://examples/hello.xml

http://hello.xml/



The XML Declaration

• version attribute

– required

– always has the value 1.0

• standalone attribute

– yes

– no

• encoding attribute

– UTF-8

– 8859_1

– etc.

<?xml version="1.0" standalone="yes"?>



The FOO element

• Start tag <FOO>

•

Contents "Hello XML!"• End tag </FOO>

<FOO> Hello XML!

</FOO>



greeting.xml

<?xml version="1.0" standalone="yes"?> <GREETING>

Hello XML! </GREETING>

St l h t



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



xml-stylesheet

•

Style sheets are attached via an xml-stylesheet processing instruction in the

prolog

<?xml version="1.0" standalone="yes"?> <?xml-stylesheet type="text/css"

href="greeting.css"?> <GREETING>Hello XML!</GREETING>

– type attribute has the value text/css or text/xsl

– href attribute is a URL to the stylesheet, possiblyrelative

• Can also use non-browser converters like



greeting.css

GREETING {display: block;font-size: 24pt;font-weight: bold}



A larger example: Baseballstatistics

• Examine the data

• Design a vocabulary for the data

• Write a style sheet

S l t ti ti



Sample statistics

http://cbs.sportsline.com/u/baseball/mlb/

stats.htm

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







Organizing the Data

• XML documents are trees.

• XML elements contain other elements as

well as text

• Within these limits there's more than oneway to organize the data

– Hierarchically

– Relationally

– Objects



What is the Root Element

• The League?

• The Season?

• A custom Document element?



The Root Element

<?xml version="1.0"?> <SEASON> </SEASON>

• Choose SEASON for the root element

• Everything else will be a descendant of SEASON

• This is not the only possible choice

http://examples/baseball1.xml



What are the ImmediateChildren of The root?

• Leagues?

• Teams?

• Players?

• Games?



Child Elements

<?xml version="1.0"?> <SEASON> <YEAR>

1998

</YEAR> </SEASON>




White space in XML is notespecially significant

<?xml version="1.0"?>

<SEASON><YEAR>1998</YEAR></SEASON>



Leagues

• Major league baseball is divided intotwo leagues

• Each league has – a name

– three divisions




Divisions

• Each division has

– name

–

4-6 teams




Teams

• Each team has

– Name

–

City – Players




Player Data

• Each player has

– First name

–

Last name – Position

– Statistics




Player Batting Statistics

• G Games Played

• GS Games Started

• AB At Bats

• R Runs• H Hits

• 2B Doubles

•

3B Triples• HR Home Runs

• RBI Runs Batted In

• 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




What does a player look like

• Long names vs. short names

Th C l t 1998 M j








The Complete 1998 MajorLeague

• Long version

http://metalab.unc.edu/xml/examples/1998statistics.xml

http://metalab.unc.edu/xml/examples/1998statistics.xml



A Style Sheet

• 1998shortstats.xml

• baseballstats.css

• <?xml-stylesheet type="text/css"href="baseballstats.css"?>

• styled1998shortstats.xml

http://examples/1998shortstats.xml

http://examples/styled1998shortstats.xml



http://examples/styled1998shortstats.xml




Cascading Style Sheets

• Partially supported by Mozilla and IE5.0

•Full W3C Recommendation



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}

A t l l f th YEAR

http://examples/cssstats.xml



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}

St l R l f Di i i d L

http://examples/cssstats2.xml



Style Rules for Division and LeagueNames

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}

Alt t St l R l f Di i i




Alternate Style Rules for Divisionand League Names

LEAGUE_NAME, DIVISION_NAME {display: block;text-align: center;font-weight: bold}

LEAGUE_NAME {font-size: 28pt }DIVISION_NAME {font-size: 24pt }




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}

Style Rules for Players




Style Rules for PlayersTEAM {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}

Finished Style Sheet




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}

Possible Extensions




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 collapsibleoutline view would be nice.

• Pitcher stats should be separated frombatter stats.



Possible Solutions

• CSS Level 2

• XSL

• XSL + JavaScript



Well-formedness Rules• Open and close all tags

• Empty tags end with />

• There is a unique root element

• Elements may not overlap

• Attribute values are quoted

• < and & are only used to start tags andentities

• Only the five predefined entity references

are used



Open and close all tags



Empty tags end with />

• <BR/>, <HR/>, and <IMG/> insteadof <BR>, <HR>, and <IMG>

•

Web browsers deal inconsistently withthese

• Can use <BR></BR> <HR></HR>

<IMG></IMG> instead



There is a unique root element

• One element completely contains allother elements of the document

•

This is HTML in HTML files

• XML Declaration is not an element

<?xml version="1.0" standalone="yes"?>

<GREETING>

Hello XML!

</GREETING>



Elements may not overlap

• If an element contains a start tag foran element, it must also contain thecorresponding end tag

• Empty elements may appear anywhere

• Every non root element has a parent

element



Attribute values are quoted

• Good:

– <AHREF="http://metalab.unc.edu/xml/">

• Bad:

– <A HREF=http://metalab.unc.edu/xml/>

< and & are only used to start tags



y gand entities

• Good: <H1>O'Reilly & Associates</H1>

• Bad: <H1> O'Reilly &

Associates</H1>

• Good:

– <CODE>for (int i = 0; i <=args.length; i++ ) { </CODE>

• Bad:

–

<CODE>for (int i = 0; i <= args.length;++

Only the five predefined entity



Only the five predefined entityreferences are used

• Good:

– &

– <

– >

– "

– '

• Bad:

– ©

– ®

– &tm;

– α

– é

–

– etc.



DTDs and Validity

• A Document T ype Definition describesthe elements and attributes that mayappear in a document

• Validation compares a particulardocument against a DTD

• Well-formedness is a prerequisite for

validity



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



The importance of validation

• Ensures that data is correct beforefeeding 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



A DTD for greeting.xml

• greeting.xml:

<?xml version="1.0"?> <GREETING> Hello XML! </GREETING>

• greeting.dtd:

<!ELEMENT GREETING (#PCDATA)>

D t T D l ti



Document Type Declarations <?xml version="1.0"?>

<!DOCTYPE GREETING SYSTEM "greeting.dtd"> <GREETING> Hello XML!

</GREETING> • specifies the root element

• gives a URL for the DTD

Invalid Documents



Invalid Documents• Valid: <GREETING> various random text but no markup </GREETING>

• Invalid: anything else including <GREETING> <sometag>various random text</sometag> <someEmptyTag/>

</GREETING>

– or <GREETING> <GREETING>various random

text</GREETING>



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.html

• Browsers

l l



Element Declarations

• Each tag must be declared in a<!ELEMENT> declaration.

• A <!ELEMENT> declaration gives thename and content model of theelement

• The content model uses a simple

regular expression-like grammar toprecisely specify what is and isn'tallowed in an element

Content Specifications



Content Specifications

•

ANY • #PCDATA

• Sequences

• Choices

• Mixed Content

• Modifiers

• Empty

ANY



ANY

<!ELEMENT SEASON ANY>

• A SEASON can contain any childelement and/or raw text (parsedcharacter data)

#PCDATA



#PCDATA

<!ELEMENT YEAR (#PCDATA)>

• Parsed Character Data; i.e. raw text,no markup

#PCDATA



#PCDATA

• Valid: <YEAR>1999</YEAR> <YEAR>99</YEAR> <YEAR>1999 C.E.</YEAR> <YEAR>

The year of our Lord one thousand, ninehundred, and ninety-nine

</YEAR>

• Invalid: <YEAR> <MONTH>January</MONTH> <MONTH>February</MONTH>

<MONTH>March</MONTH> <MONTH>April</MONTH> <MONTH>May</MONTH> <MONTH>June</MONTH> <MONTH>July</MONTH>

<MONTH>August</MONTH> <MONTH>September</MONTH> <MONTH>October</MONTH> <MONTH>November</MONTH> <MONTH>December</MONTH>

</YEAR>

Child El t



Child Elements

• To declare that a LEAGUE elementmust have a LEAGUE_NAME child:

<!ELEMENT LEAGUE (LEAGUE_NAME)>

<!ELEMENT LEAGUE_NAME (#PCDATA)>

S



Sequences

• Separate multiple required childelements with commas; e.g.

<!ELEMENT SEASON (YEAR, LEAGUE,

LEAGUE)>

<!ELEMENT LEAGUE (LEAGUE_NAME,DIVISION, DIVISION, DIVISION)>

O M Child



One or More Children +

<!ELEMENT DIVISION_NAME (#PCDATA)>

<!ELEMENT DIVISION (DIVISION_NAME,TEAM+)>

Z M Child *



Zero or More Children *

<!ELEMENT TEAM (TEAM_CITY, TEAM_NAME,PLAYER*)>

<!ELEMENT TEAM_CITY (#PCDATA)>

<!ELEMENT TEAM_NAME (#PCDATA)>

Z O Child ?



Zero or One Children ? <!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?)

>

Fi i h d DTD



Finished DTD

Ch i



Choices

<!ELEMENT PAYMENT (CASH |CREDIT_CARD)>

<!ELEMENT PAYMENT (CASH |

CREDIT_CARD | CHECK)>

Grouping With Parentheses



• Parentheses combine several elements

into a single element.

• Parenthesized element can be nestedinside other parentheses in place of a

single element.

• The parenthesized element can besuffixed with a plus sign, a comma, or a

question mark. <!ELEMENT dl (dt, dd)*> <!ELEMENT ARTICLE (TITLE, (P | PHOTO |

GRAPH | SIDEBAR | PULLQUOTE |

SUBHEAD)*, BYLINE?)>

Mixed Content



Mixed Content

• Both #PCDATA and child elements in achoice

<!ELEMENT TEAM (#PCDATA | TEAM_CITY |

TEAM_NAME | PLAYER)*>

• #PCDATA must come first

•#PCDATA cannot be used in asequence

Empty elements



Empty elements

<!ELEMENT BR EMPTY>

<!ELEMENT IMG EMPTY>

<!ELEMENT HR EMPTY>

Internal DTDs



Internal DTDs

<?xml version="1.0"?> <!DOCTYPE GREETING [ <!ELEMENT GREETING (#PCDATA)>

]> <GREETING> Hello XML!

</GREETING>

Internal DTD Subsets



Internal DTD Subsets

<?xml version="1.0"?> <!DOCTYPE GREETING SYSTEM

"greeting.dtd" [

<!ELEMENT GREETING (#PCDATA)> ]> <GREETING> Hello XML!

</GREETING> • Internal declarations override

external declarations

Programming with XML



Programming with XML

• Java works best

• C, Perl, Python etc. can also be used

• Unicode support is the biggest issue

SAX the Simple API for XML



SAX, the Simple API for XML

• Event based

• Programs can plug in different parsers

The Document Object Model



j(DOM)

To Learn More: Books



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

Questions?



Questions?

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