XML & Data Structures for the Internet Yingcai Xiao

What is XML? What is it for? Examples How to write? How to validate? How to read? How to display? How to format? How to translate?

A Common Language for the Internet (free of compilation and translation)?

A Common Language for the Internet Tim Berners-Lee ASCII text (ISO/IEC ) is platform-independent. HTTP (Hyper Text Transport Protocol) e.g. GET wp.html Assembly Language for the Internet HTML (Hyper Text Markup Language) High-level language for the Internet) hyper text: text that describes other text tags: type definition of text in text WP all tags are predefined in HTML only system defined types, no user defined types Recognizable by all types of computers. (World Wide Web)

A Common Language for the Internet  XML (eXtensible Markup Language) Allow user defined tags (types)  SOAP (Simple Object Access Protocol) Standards for defining objects for the Internet Based on XML  WSDL (Web Service Description Language) Standards for describing web services for the Internet Based on XML

(XML) Web Services Proxy of Interface 2 Client 2 Application 1 UDDI Registry 1 WSDL Interface 1 UDDI Registry 2 Application 2WSDL Interface 2 SOAP WEB Proxy of Interface 1 Client 1 A Web service is an application that exposes Web methods over the Web.

. What is XML?

 Extensible Markup Language.  De facto data language for the Internet.  HTML expresses appearance; XML describes data and its structure.  Text based (platform-independent).  Object-oriented data representation.  Has no predefined tags.  Provides rules to format data.. XML

XML Example (Guitars.xml) Gibson SG 1977 Tobacco Sunburst Rosewood Fender Stratocaster Black Maple

XML Example (Guitars.xml)  Document element (root): Guitars.  Guitar elements are children of Guitars.  Make contain data.  Empty element:  Nested elements.  The content of an XML document can be viewed as a tree.  Attributes

. How to define an XML data structure?

XML Description  XML Elements: text-based object-oriented data (object)  Error checking?  Text-based object-oriented type (class) definition?  Early days: document type definitions (DTDs).  Today: XML Schema Definitions (XSDs).  Schema: a collection of meta data.  Meta data: data that describes data.  XSD is an XML-based language for describing XML documents and the types that they contain.

Example: Guitars.xsd

. How to validate XML data?

Examples\c13\Validate\ Typo => xsd:Year should be xsd:string run.bat Validate Guitars.xml Guitars.xsd run-bad-xml.bat Validate Guitars-Missing-Make.xml Guitars.xsd Example: Guitars.xsd

. How to read XML data?

XML Parsers  Most XML parsers implement one of two popular APIs: DOM or SAX.  DOM: Document Object Model Level-2-Core.  SAX: Simple API for XML, unofficial,  Examples of using XmlDocument: Validate ReadXml XmlView Transform Quotes ExpressAnalyzer

ReadXml.cs (also see XmlView) using System; using System.Xml; class MyApp { static void Main () { XmlDocument doc = new XmlDocument (); doc.Load ("Guitars.xml"); XmlNodeList nodes = doc.GetElementsByTagName ("Guitar"); foreach (XmlNode node in nodes) { Console.WriteLine(“Maker {0}; Model {1}", node["Make"].InnerText, node["Model"].InnerText); }

 XML Path Language  For addressing parts of an XML document.  “/Guitars/Guitar” is an XPath expression.  XPath

. How to display XML data with styles?

XSL is a language for expressing style sheets. Adopted from CSS, a file that describes how to display an XML document of a given type.CSS Styling requires a source XML documents, containing the information that the style sheet will display and the style sheet itself which describes how to display a document of a given type. It supports: Formatting Objects. It also adds a transformation language for XML documents: XSLT. Example: XML\Quotes\Quotes.xsl tes/quotes.aspx/ XSL

. How to translate XML into other languages?

 Extensible Stylesheet Language Transformations.  Converting XML documents into HTML documents.  Converting HTML documents into other XML documents.  Example XML\Transform\Transform.cs XSL Transformations (XSLT)

How to Program the Internet? (Write code that runs on the Internet) Web Service & Cloud Computing