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

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

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

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

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

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

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)

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

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>

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

Example –Wikipedia RESTful API reference Example 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

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

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']

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

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