XML: Introduction to XML

1
XMLIntroduction to XML

• Ethan Cerami
• New York University

2
Road Map

• What is XML?
• A Brief Overview
• Origins of XML
• Creating XML Documents
• Basic Rules
• Example XML Documents
• Case Studies

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Brief Overview of XMLXML v. HTML
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What is XML?

• XML eXtensible Markup Language
• "XML, to a certain extent, is HTML done right."
  - Simon St. Laurent
• XML is HTML on steroids.
• XML
• Extensible can be extended to lots of different
  applications.
• Markup language language used to mark up data.
• Meta Language Language used to create other
  languages.

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XML v.HTML

• The best way to first understand XML is to
  contrast it with HTML.
• XML is Extensible
• HTML restricted set of tags, e.g. ltTABLEgt,
  ltH1gt, ltBgt, etc.
• XML you can create your own tags
• Example Put a library catalog on the web.
• HTML You are stuck with regular HTML tags, e.g.
  H1, H3, etc.
• XML You can create your own set of tags
  TITLE, AUTHOR, DATE, PUBLISHER, etc.

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Book Catalog in HTML
HTML conveys the look and feel of your
page. As a human, it is easy to pick out the
publisher. But, how would a computer pick out
the publisher? Answer XML

• ltHTMLgt
• ltBODYgt
• ltH1gtHarry Potterlt/H1gt
• ltH2gtJ. K. Rowlinglt/H2gt
• ltH3gt1999lt/H3gt
• ltH3gtScholasticlt/H3gt
• lt/BODYgt
• lt/HTMLgt

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Book Catalog in XML

• ltBOOKgt
• ltTITLEgtHarry Potterlt/TITLEgt
• ltAUTHORgtJ. K. Rowlinglt/AUTHORgt
• ltDATEgt1999lt/DATEgtltPUBLISHERgtScholasticlt/PUBLISHE
  Rgt
• lt/BOOKgt

Look at the new tags! A Human and a computer can
now easily extract the publisher data.
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XML v. HTML

• General Structure
• Both have Start tags and end tags.
• Tag Sets
• HTML has set tags
• XML lets you create your own tags.
• General Purposes
• HTML focuses on "look and feel
• XML focuses on the structure of the data.
• XML is not meant to be a replacement for HTML.
  In fact, they are usually used together.

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Origins of XML
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Origins of XML

• XML is based on SGML Standard Generalized
  Markup Language
• SGML
• Developed in the 1970s
• Used by big organizations IRS, IBM, Department
  of Defense
• Focuses on content structure, not look and feel
• Good for creating catalogs, manuals.
• Very complex

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Origins of XML

• XML SGML-Lite 20 of SGML's complexity, 80
  of its capacity.
• HTML and XML are both based on SGML.

SGML
HTML
XML
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XML and the W3C

• XML is an official standard of the World Wide Web
  Consortium (W3C)
• The Official Version is 1.0
• Official information is available at
• http//www.w3.org/XML/
• The Official spec is available at
• http//www.w3.org/TR/1998/REC-xml-19980210
• The Official XML FAQ
• http//www.ucc.ie/xml/
• W3C sponsors many projects which seek to enhance
  and improve on XML.

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Creating XML DocumentsBasic Rules
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Basic Definitions

• Tag a piece of markup
• Example ltPgt, ltH1gt, ltTABLEgt, etc.
• Element a start and an end tag
• Example ltH1gtHellolt/H1gt
• HTML Code
• ltPgtThis is a ltBgtsamplelt/Bgt paragraph.
• This code contains
• 3 tags, ltPgt, ltBgt, and lt/Bgt
• However, it only contains one element ltBgtlt/Bgt

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Rule 1 Well-Formedness

• XML is much more strict than HTML.
• XML requires that documents be well-formed
• every start tag must have an end tag
• all tags must be properly nested.
• XML Code
• ltPgtThis is a ltBgtsamplelt/Bgt paragraph.lt/Pgt

Note the end lt/Pgt
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Rule 1 Well-Formedness

• Another HTML Example
• ltbgtltigtThis text is bold and italiclt/bgtlt/igt
• This will render in a browser, but contains a
  nesting error.
• XML Code (with proper nesting)
• ltbgtltigtThis text is bold and italiclt/igtlt/bgt

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Rule 2 XML is Case Sensitive

• XML is Case Sensitive.
• HTML is not.
• The following is valid in HTML
• ltH1gtHello Worldlt/h1gt
• This will not work in XML. Would result in a
  well-formedness error
• H1 does not have a matching end H1 tag.

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Rule 3 Attributes must be quoted.

• In HTML you can get away with doing the
  following
• ltFONT FACEARIAL SIZE2gt
• In XML, you must put quotes around all your
  attributes
• ltBOOK ID894329gtHarry Potterlt/BOOKgt

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Examples
20
Examples

• To get a feel for XML, lets take a look at
  several examples
• An XML Memo
• CD Catalog
• Plant Catalog
• Restaurant Menu

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Example 1 A Memo

• lt?xml version"1.0" encoding"ISO8859-1" ?gt
• ltnotegt
• lttogtClasslt/togt
• ltfromgtEthanlt/fromgt
• ltheadinggtIntroductionlt/headinggt
• ltbodygtThis is an XML document!lt/bodygt
• lt/notegt

This XML Note could be part of a message board
application.
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Example 2 CD Collection

• lt?xml version"1.0" encoding"ISO8859-1" ?gt
• ltCATALOGgt
• ltCDgt
• ltTITLEgtEmpire Burlesquelt/TITLEgt
• ltARTISTgtBob Dylanlt/ARTISTgt
• ltCOUNTRYgtUSAlt/COUNTRYgt
• ltCOMPANYgtColumbialt/COMPANYgt
• ltPRICEgt10.90lt/PRICEgt
• ltYEARgt1985lt/YEARgt
• lt/CDgt

A Disclaimer I did not pick these CDs! I just
got the example off the web -)
Continued...
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ltCDgt ltTITLEgtHide your heartlt/TITLEgt
ltARTISTgtBonnie Tylorlt/ARTISTgt
ltCOUNTRYgtUKlt/COUNTRYgt ltCOMPANYgtCBS
Recordslt/COMPANYgt ltPRICEgt9.90lt/PRICEgt
ltYEARgt1988lt/YEARgt lt/CDgt ltCDgt
ltTITLEgtUnchain my heartlt/TITLEgt ltARTISTgtJoe
Cockerlt/ARTISTgt ltCOUNTRYgtUSAlt/COUNTRYgt
ltCOMPANYgtEMIlt/COMPANYgt ltPRICEgt8.20lt/PRICEgt
ltYEARgt1987lt/YEARgt lt/CDgt lt/CATALOGgt
Note that indentation helps you follow the flow
of the document.
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Example 3 A Plant Catalog

• lt?xml version"1.0" encoding"ISO8859-1" ?gt
• ltCATALOGgt
• ltPLANTgt
• ltCOMMONgtBloodrootlt/COMMONgt
• ltBOTANICALgtSanguinaria canadensislt/BOTANICALgt
• ltZONEgt4lt/ZONEgt
• ltLIGHTgtMostly Shadylt/LIGHTgt
• ltPRICEgt2.44lt/PRICEgt
• ltAVAILABILITYgt031599lt/AVAILABILITYgt
• lt/PLANTgt

Continued...
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ltPLANTgt ltCOMMONgtColumbinelt/COMMONgt
ltBOTANICALgtAquilegia canadensislt/BOTANICALgt
ltZONEgt3lt/ZONEgt ltLIGHTgtMostly Shadylt/LIGHTgt
ltPRICEgt9.37lt/PRICEgt ltAVAILABILITYgt030699lt/AV
AILABILITYgt lt/PLANTgt ltPLANTgt
ltCOMMONgtMarsh Marigoldlt/COMMONgt
ltBOTANICALgtCaltha palustrislt/BOTANICALgt
ltZONEgt4lt/ZONEgt ltLIGHTgtMostly Sunnylt/LIGHTgt
ltPRICEgt6.81lt/PRICEgt ltAVAILABILITYgt051799lt/AV
AILABILITYgt lt/PLANTgt lt/CATALOGgt
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Example 4 Restaurant Menu

• lt?xml version"1.0" encoding"ISO8859-1" ?gt
• ltbreakfast-menugt
• ltfoodgt
• ltnamegtBelgian Waffleslt/namegt
• ltpricegt5.95lt/pricegt
• ltdescriptiongttwo of our famous Belgian
  Waffles with plenty of real maple
  syruplt/descriptiongt
• ltcaloriesgt650lt/caloriesgt
• lt/foodgt

Continued...
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ltfoodgt ltnamegtStrawberry Belgian
Waffleslt/namegt ltpricegt7.95lt/pricegt
ltdescriptiongtlight Belgian waffles covered
with strawberrys and whipped cream
lt/descriptiongt ltcaloriesgt900lt/caloriesgt
lt/foodgt ltfoodgt ltnamegtBerry-Berry Belgian
Waffleslt/namegt ltpricegt8.95lt/pricegt
ltdescriptiongtlight Belgian waffles covered
with an assortment of fresh berries and
whipped cream lt/descriptiongt
ltcaloriesgt900lt/caloriesgt lt/foodgt
Continued...
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ltfoodgt ltnamegtFrench Toastlt/namegt
ltpricegt4.50lt/pricegt ltdescriptiongtthick
slices made from our homemade sourdough bread
lt/descriptiongt ltcaloriesgt600lt/caloriesgt
lt/foodgt ltfoodgt ltnamegtHomestyle
Breakfastlt/namegt ltpricegt6.95lt/pricegt
ltdescriptiongttwo eggs, bacon or sausage, toast,
and our ever-popular hash brownslt/descriptiongt
ltcaloriesgt950lt/caloriesgt lt/foodgt lt/breakfast-m
enugt
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Case Studies
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Applications of XML

• Widely used today in major applications
• Search Engines
• News Distribution
• E-Commerce
• Real Estate
• Genetics
• Defense Department Applications

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Case Study 1Search the Web
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Case Study 1 Web Search

• Scenario
• You want to offer a web search functionality for
  your site.
• You want control over the look and feel of the
  search results.
• You do not want to support your own database of
  millions of web sites.

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Case Study 1 Web Search

• XML to the Rescue
• Several companies provide XML Access to their Web
  Search Databases.
• For example
• Open a network connection and send search
  criteria.
• Third Party returns results in XML.

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How it Works

• How it works
• User initiates a search request.
• Servlet is invoked.
• Servlet opens a network connection to Third Party
  and passes user search criteria.
• Third Party searches is database, and returns an
  XML document.
• Servlet transforms XML into HTML and returns to
  user.

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How it Works
Search Criteria
Search Criteria
Browser
Servlet
Third Party Web Database
XML
HTML
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Case Study 2Price Comparison
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Case Study 2 Price Comparison

• Scenario
• You want to create a site that compares prices of
  books.
• For example, a user enters a book title, and your
  page displays the price at bn.com, amazon.com,
  bestbuy.com, etc.
• User can choose the cheapest price.

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How it might work

• How it works
• User sends book title
• Servlet makes three concurrent connections and
  queries the bookstores
• Amazon, bn.com, bestbuy.com
• Each Bookstore returns results in a standard XML.
• Servlet parses XML and creates a small price
  comparison table.

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How it might work
Amazon
XML
Search Criteria
Browser
Servlet
BN.com
XML
HTML
BestBuy
XML
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Case Study 3 Genomics
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Case Study 3 Genomics

• Bioinformatic Sequence Markup Language (BSML)
• BSML provides a standard DTD for representing
  genes and the DNA sequences that make up that
  gene.
• This data can then be viewed via an XML Genome
  Browser (http//www.labbook.com)
• The next three slides show an excerpt of BSML for
  the gene that regulates insulin production.

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lt?xml version"1.0"?gt lt!DOCTYPE Bsml SYSTEM
"BSML2_2.DTD"gt ltBsmlgt ltDefinitionsgt ltSequencesgt ltS
equence id"G186439" title"HUMINSR"
molecule"rna ic-acckey"M10051" length"4723"
representation"raw" topology"linear"
strand"ds" comment"Human insulin receptor
mRNA, complete cds."gt ltAttribute name"version"
content"M10051.1 GI186439"/gt ltAttribute
name"source" content"Human placenta, cDNA to
mRNA, clones lambda-IR1-15."/gt ltAttribute
name"organism" content"Homo sapiens"/gt
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ltFeature-tablesgt ltFeature-tablegt
ltReference dbxref"85176928" title"1
(bases 1 to 4723)"gt ltRefAuthorsgt
Ebina,Y., Ellis,L., Jarnagin,K., Edery,M.,
Graf,L., Clauser,E., Ou,J.-H., Masiarz,F.,
Kan,Y.W., Goldfine,I.D., Roth,R.A. and
Rutter,W.J. lt/RefAuthorsgt ltRefTitlegt
The human insulin receptor cDNA the structural
basis for hormone-activated transmembrane
signalling lt/RefTitlegt
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ltSeq-datagt ggggggctgcgcggccgggtcggtgcgcacacga Ga
aggacgcgcggcccccagcgctcttgggggccgcctcggagcat Acccc
cgcgggccagcgccgcgcgcctgatccgaggagaccccgcg Ctcccgca
gccatgggcaccgggggccggcggggggcggcggccgc Gccgctgctgg
tggcggtggccgcgctgctactgggcgccgcgggcc Cctgtaccccgga
gaggtgtgtcccggcatggatatccggaacaacctc Actaggttgcatg
agctggagaattgctctgtcatcgaaggacacttgcag atactcttgat
gttcaaaacgaggcccga
DNA Sequences!