What is a web service?  A remote procedure call (RPC) over HTTP.  A web-accessible operation that takes input and returns results in XML.  Like a web page, but just the data with no presentation specifications.  Web definitions Web definitions

Importance of Web Services  Larry Page, on why Google introduced its search API: “Within a few years, there will be more programs (agents) accessing Google than people accessing Google.”

Without Web Services: Content and Presentation mixed Database Servlet html Data can only be viewed in forms provided by Server. Data left hidden in database. Scrapers not robust or ethical.

Web Services allow 3 rd parties to display data how ever they want Database Service Servlet AServlet CServlet B xml html

Examples  Bookstores Using Amazon API  If Google Scholar had a service, could develop graph view, etc.

Web Services Allow for Aggregators Database A Database BDatabase C Database D Service B Service A Service C Service D Aggregator Servlet html xml

Competing Web Service Standards  WSDL, SOAP, UDDI  REST  XML-RPC

WSDL, SOAP, UDDI  WSDL – Web Service Description Language  SOAP – Simple Object Access Protocol  UDDI – Universal Description, Discovery, and Integration

IDE Support Programmer writes class in favorite language Programmer marks as “web service” IDE generates wsdl file and soap service walla! Writing a Service Writing a Client Programmer provides uri of some web service IDE generates client stub Programmer makes calls to service methods.

XML is the plumbing Client Server JavaC# Generated SOAP Plumbing: programmers need not worry