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Computer Science E-75Building Dynamic Websites
Harvard Extension Schoolhttp://www.cs75.net/
Lecture 3: XML
David J. Malan
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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