Web Services CO5027

What are Web Services “a software system designed to support interoperable machine-to-machine interaction over a network “ [W3C] Software component which runs on a remote server providing a defined set of functions for incorporation into a local system Published resources which can be used by external clients or servers.

Why Web Services? “Web services provide a standard means of interoperating between different software applications, running on a variety of platforms and/or frameworks” [W3C] eCommerce and eBusiness rely on intercommunication between clients and business. Web services make business processes and services available without need for shipping complex application software or having complex transaction based website.

Terminology Services and agents The service is the abstract definition of the nature and functions that are expected of the web service. The agent is the actual software component which provides the service Requesters and providers Provider entity is the owner of the web service which is made available as the providers agent. Requester entity is the end user of the web service made possible using the requesters agent. Semantics The unambiguous definition of the expected behaviour of the web service

How?

UDDI Universal Discovery, Description and Integration “UDDI creates a standard interoperable platform that enables companies and applications to quickly, easily, and dynamically find and use Web services over the Internet. “ [Oasis-IDDI] Allows requester entity to find and incorporate an appropriate web service in their application. Uses XML to communicate.

Web service repositories Online web interface to find web services Some will provide UDDI interface Some use UDDI to build their site Most provide facility to test the web service All provide WSDL http://www.cs.washington.edu/woogle http://www.xmethods.net http://www.webservicex.net

WSDL Web Service Description Language Provides all the information needed to allow an external system to use a system. Similar to the class definition in programming terms. Web tools can use the WSDL spec for a service to provide the interface to the service. Communicates using XML

SOAP Simple Object Access Protocol Message protocol allowing programs from one system to communicate with programs on another system. Uses XML as communication medium.

Example SOAP request POST /CurrencyConvertor.asmx HTTP/1.1 Host: www.webservicex.net Content-Type: text/xml; charset=utf-8 Content-Length: length SOAPAction: http://www.webserviceX.NET/ConversionRate <?xml version="1.0" encoding="utf-8"?> <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <ConversionRate xmlns="http://www.webserviceX.NET/"> <FromCurrency>GBP</FromCurrency> <ToCurrency>EUR</ToCurrency> </ConversionRate> </soap:Body> </ soap:Envelope>

Example SOAP Response HTTP/1.1 200 OK Content-Type: text/xml; charset=utf-8 Content-Length: length <?xml version="1.0" encoding="utf-8"?> <soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/"> <soap:Body> <ConversionRateResponse xmlns="http://www.webserviceX.NET/"> <ConversionRateResult>1.4732</ConversionRateResult> </ConversionRateResponse> </soap:Body> </soap:Envelope>

Using a Web service Find your web service Retrieve the WSDL specification for the Web Service Use the specification to produce an interface to the service. Start using the service

Type of access to a web service HTTP GET or POST Uses simple xhtml form to interface with service Service returns xml which will not be in a form suitable for direct display Only works for simple data types SOAP specification Consumer must use correct protocol to access service. Usually requires program to interface.

e.g. Language Translation Web service is: http://www.webservicex.net/TranslateService.asmx Accessing this page returns a generic page describing the service and how to use it, with a link to a detailed description. Details shows SOAP, HTTP GET & POST are all available. To retrieve WSDL specification append the suffix '?wsdl' to the URL.

Simple HTTP GET interface See translate.html

Using the SOAP binding. Use tool to import WSDL and create a proxy class. Use .NET page to call the functions in the proxy class. The proxy calls the real web service and passes back the reply to your page.

Examples Language Translator Currency Converter Global Weather Lotto number chooser Google

Language Translator

Currency Converter

Global weather

Lotto number chooser

Google

Subscription based web services Michelin route mapping (ViaMichelin) Route planning and mapping Amazon Simple Storage Service (Amazon S3) Internet storage with several web interfaces (incl. Web service) 15c /month stored, 20c/month transfer Amazon Elastic Compute Cloud Dynamic virtual machine service based on Amazon S3 for storage of virtual machines Fees for storage of VMs and fees for running time.