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Introduction to Web Services: Standards, Protocols, and Applications

This document explores the evolution of web services within the context of distributed computing, moving beyond traditional human-centered interactions of the World Wide Web to automated system-to-system interactions. It covers essential web service protocols like SOAP and REST, highlighting their roles in data interchange formats such as XML and JSON. The content also includes coding examples and practical applications of web services, aiming to provide a comprehensive understanding of how web services facilitate automated e-commerce and resource sharing.

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Introduction to Web Services: Standards, Protocols, and Applications

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  1. Introduction to Web Services Asst. Prof. Chaiporn Jaikaeo, Ph.D. chaiporn.j@ku.ac.th http://www.cpe.ku.ac.th/~cpj Computer Engineering Department Kasetsart University, Bangkok, Thailand

  2. Traditional World-Wide-Web • Designed for human-to-app interactions • Information sharing • (Non-automated) E-commerce • Built on top of • HTTP – for data transfer • HTML – for representing document

  3. What's Next? • Try taking humans out of the loop • Systematic application-to-application interaction over the web • Automated e-commerce • Resource sharing • Distributed computing • Web services • (another) effort to build distributed computing platform for the web

  4. Web Services vs. Web Apps • Web application • Provides service directly to user • Web service or (Web API) • Provides service to other programs browser web server HTTP web server(service provider) app(service user) HTTP

  5. Web Service Protocols • Simple Object Access Protocol (SOAP) • Service requests and responses are always done via XML messages, called SOAP envelope • Formally supported by World Wide Web Consortium (W3C) • Representational State Transfer (REST) • Service requests are done via generic HTTP commands: GET, POST, PUT, DELETE • Simpler set of operations

  6. Other Web Service Protocols • Web feeds • RSS • Atom • Remote procedure call • JSON-RPC • XML-RPC • JavaScript

  7. Sample SOAP Message • E.g., message requesting IBM stock price POST /InStock HTTP/1.1 Host: www.example.org Content-Type: application/soap+xml; charset=utf-8 Content-Length: 299 <?xml version="1.0"?> <soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope"> <soap:Header> </soap:Header> <soap:Body> <m:GetStockPrice xmlns:m="http://www.example.org/stock"> <m:StockName>IBM</m:StockName> </m:GetStockPrice> </soap:Body> </soap:Envelope> HTTP Header SOAP Envelope Desired operation(Verb) Object of interest(Noun)

  8. Sample REST Request • E.g., message requesting IBM stock price The above corresponds to the URL GET /stock/ibm HTTP/1.1 Host: www.example.org HTTP Header Desired operation(Verb) Object of interest(Noun) http://www.example.org/stock/ibm

  9. Data Interchange Formats • XML – eXtensible Markup Language • E.g., RSS, Atom • Large collection of libraries for processing XML <?xml version="1.0" encoding="ISO-8859-1"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://purl.org/rss/1.0/"> <title>Slashdot</title> <link>http://slashdot.org/</link> <description>News for nerds, stuff that matters</description> <dc:subject>Technology</dc:subject> <items> <rdf:Seq> <rdf:li rdf:resource="http://it.slashdot.org/story/11/02/14/0337211/Recent-HP-Laptops-Shipped-CPU-Choking-Wi-Fi-Driver?from=rss" /> </ref:Seq> </items> </rdf:RDF>

  10. Data Interchange Formats • JSON – JavaScript Object Notation • Can be directly evaluated in JavaScript • Typically smaller than XML • Libraries for other languages are also available { "Person": { "firstName": "John", "lastName": "Smith", "age": 25, "Address": { "streetAddress":"21 2nd Street", "city":"New York", "state":"NY", "postalCode":"10021" }, "PhoneNumbers": { "home":"212 555-1234", "fax":"646 555-4567" } } } <Person> <firstName>John</firstName> <lastName>Smith</lastName> <age>25</age> <Address> <streetAddress>21 2nd Street</streetAddress> <city>New York</city> <state>NY</state> <postalCode>10021</postalCode> </Address> <PhoneNumbers> <home>212 555-1234</home> <fax>646 555-4567</fax> </PhoneNumbers> </Person> XML JSON

  11. Example –Wikipedia • RESTful • API reference • http://en.wikipedia.org/w/api.php • Example • http://en.wikipedia.org/w/api.php?format=json&action=query&titles=Kasetsart%20University&prop=revisions&rvprop=content

  12. Example – HostIP.info • RESTful • Determines geographical location of the specified IP address • API documentation • http://www.hostip.info/use.html • Example • http://api.hostip.info/get_json.php?ip=158.108.2.71

  13. Coding Example • E.g., accessing HostIP.info from Python import sys import json from urllib import urlencode from urllib2 import urlopen response = urlopen('http://api.hostip.info/get_json.php?' + urlencode({ 'ip' : sys.argv[1], })) data = json.loads(response.read()) print 'IP Address: %s' % data['ip'] print 'City: %s' % data['city'] print 'Country: %s' % data['country_name']

  14. Mashups • A mashup is a webpage or application that offers new services by combining data or functionality from two or more sources • Main characteristics of mashups • Combination • Visualization • Aggregation • They aim to make existing data more useful • Example: Wikipediavision • Google Maps + Wikipedia • http://www.lkozma.net/wpv/index.html

  15. More Resources • Search engine for web APIs and mashups • http://www.programmableweb.com

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