Web Information Systems XML

XML
Web Information Systems - 2015

XML
 eXtensible Markup Language
 w3c standard
 Why?
 Store and transport data
 Easy data exchange
 Create more languages
 WSDL (Web Service Description Language)
 RDF (Resource Description Framework)
 RSS (Really Simple Syndication)
 Self-describing data
 Easy to learn
 Must learn

3 Major Components
 XML
 XSL (eXtensible Stylesheet Language)
 Style sheet language for XML documents
 XSD (XML Schema Definition)
 Describes the structure of an XML document

XML Document
<?xml version="1.0"?>

<note>
<to>Tove</to>
<from source=”contacts”>Jani</from>
<heading>Reminder</heading>
<body>Don't forget me this weekend!</body>
</note>
Processing Instruction
Comment
Element
Attribute

XML Documents
 Well formed and Valid
 Well formed
 Should only contain one root element
 All tags should have corresponding end tag
 Tags never overlap(<author><name> …
</author></name>)
 Attributes must be quoted
 Valid
 Must be well formed and conforms to the schema

XML Documents
 Has tree structure
 Tags are case sensitive
 <name> is different from <Name>
 Comments

XML Elements
 Can contain
 Other elements
 Text
 Attributes
 Valid names
 <name>, <first_name>, <first2names>
 Invalid names
 <2nd_name>, <$amount>, <first name>

XML elements and Attributes
 Data goes as elements
 <person><name>john</name></person>
 Meta data goes as attributes
 <image type='gif'><name>graph.gif</name></image>

1.0 vs 1.1
• 1.0 – everything not permitted is forbidden
• 1.1 – everything not forbidden is permitted
• 1.0 is compatible with 1.1, not vise-versa
• Forward compatible
• Does not affect to English documents

XML Namespaces
 There can be common elements in multiple domains
 File in hardware and office
<file>
<length>18</length>
<price>3.69</price>
<file>
<file>
<content>Employee data</content>
<numberOfPages>25</numberOfPages>
</file>

XML Namespaces
 How to distinguish?
 Solution : namespaces
<h:file xmlns:h="http://www.hardware.com/">
<h:length>18</h:length>
<h:price>3.69</h:price>
<h:file>
<o:file xmlns:o="http://www.office.com/people">
<o:content>Employee data</o:content>
<o:numberOfPages>25</o:numberOfPages>
</o:file>

XML Parsers
• A piece of software which reads the content from the XML documents and present it
to the application
• Implementing xml parser
• Java way
• SAX (Simple API for XML)
• DOM (Document Object Model)
• StAX (Streaming API for XML)

XML Parsers
Feature StAX SAX DOM
API Type Pull, Streaming Push, Streaming In memory tree
Ease of Use High Medium High
XPath Capability No No Yes
CPU and Memory
Efficiency
Good Good Varies
Forward Only Yes Yes No
Read XML Yes Yes Yes
Write XML Yes No Yes
CRUD No No Yes

XSL
• XSL is a language for expressing stylesheets
• eXtensible Stylesheet Language
• XSLT (XSL Transformations)
• XPath
• XML vocabulary for specifying formatting semantics

XPath
<?xml version="1.0" encoding="UTF-8"?>
<bookstore>
<book>
<title lang="en">Harry Potter</title>
<price>29.99</price>
</book>
<book>
<title lang="en">Learning XML</title>
</book>
</bookstore>
/bookstore

XPath
<bookstore>
<book>
</book>
<book>
</book>
</bookstore>
/bookstore/book

XPath
<bookstore>
<book>
</book>
<book>
</book>
</bookstore>
//book

XPath
• Few Examples
 How to refer to the body element ?
 /note/body [ '/' means root ]
 How to get the source attribute ?
 /note/from/@source
 How to get all elements with a source attribute ?
 //*[@source]

XSLT
• A language to convert XML documents to other
formats
• w3c Recommendation
• Uses XPath

Web Information Systems XML

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