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Computer Science E-75Building Dynamic Websites

Harvard Extension Schoolhttp://www.cs75.net/

Lecture 3: XML

David J. Malan

dmalan@harvard.edu

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XML

MalanDavid

20050621

29.95

Harry Potter and the

Order of the Phoenix

J.K. Rowling

element

textstart tag

attribute

end tag

child element

value

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Extensibility

Malan

David

J

Oxford Street

33

Cambridge

MA

20050621

...

extend structurewithout breakingexisting data and

applications

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Jim Bob

graduate

Computer Science & Music

Jim Bob!

Hi my name is jim. I look like

]]>

...

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XML Declaration Optional Must appear at the very top of an XML document Used to indicate the version of the specification to

which the document conforms (and whether the

document is standalone)

Used to indicate the character encoding of thedocument

UTF-8 UTF-16 iso-8859-1

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Elements Main structure in an XML document Only one root element allowed Start Tag

Allows specification of zero or more attributes

End Tag Must match name, case, and nesting level of start tag

Name must start with letter or underscore and can containonly letters, numbers, hyphens, periods, and underscores

Jim Bob

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Content Models Element Content

...

Parsed Character Data (aka PCDATA, aka Text)Jim Bob

Mixed ContentJim J Bob

No Content

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Attributes Name

Must start with letter or underscore and can contain only letters,numbers, hyphens, periods, and underscores

Value Can be of several types, but is almost always a string Must be quoted

title="Lecture 2"match='item="baseball bat"'

Cannot contain< or&(by itself)

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PCDATA Text that appears as the content of an element Can reference entities Cannot contain< or&(by itself)

Jim Bob

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Entities Used to escape content or include content that is hard to

enter or repeated frequently

Somewhat like macros Five pre-defined entities

& < > ' " Character entities can refer to a single character by unicode

number e.g., is

Must be declared to be legal

Cannot refer to themselves

&

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CDATA Parsed in one chunk by the XML parser Data within is not checked for subelements, entities, etc. Allows you to include badly formed markup or character data

that would cause a problem during parsing

Example Including HTML tags in an XML document

Jim Bob! ... ]]>

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Comments

Can include any text inside a comment to make it easier forhuman readers to understand your document

Generally not available to applications reading the document Always begin with Cannot contain --

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SimpleXMLhttp://us2.php.net/simplexml

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DOM

Jim Bob

graduate

Document

Comment Element: students

Element: name Element: status

Element: student

Text: Jim Bob Text: graduate

Attr: idText: \n\t Text: \n

Text: \n\t\t Text: \n\tText: \n\t\t

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RSShttp://cyber.law.harvard.edu/rss/rss.html

Image from wikipedia.org.

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RSS

[...]

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XPath

/child::lectures/child::lecture[@number='0']

step axis nodetest

predicate

location path

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PizzaML

Image from junkfoodnews.net.

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Computer Science E-75Building Dynamic Websites

Harvard Extension Schoolhttp://www.cs75.net/

Lecture 3: XML

David J. Malan

dmalan@harvard.edu