1 G52IWS: Web Services Chris Greenhalgh

2 Contents The World Wide Web Web Services example scenario Motivations Basic Operational Model Supporting standards Challenges Summary See “Developing Java Web Services”, chapter 2

3 The World Wide Web Web server User Web server GET/POST request Document (usually HTML)‏ Browser communication: HTTP over TCP/IP

4 Example Web Service scenario: arranging a business trip Service requestor Travel services registry Travel reservation services provider Airline reservation System Hotel Reservation system Credit card payment system Find services Invoke services Register services Wireless device Desktop After “Developing Java Web Services” Figure 2.1

5 Scenario notes Travel reservation service provider exposes travel services via web service interfaces These are registered with (described in) the travel services registry A customer discovers the service(s) from the registry (or other search engine)‏ They then directly request things (“services”, e.g. a reservation) from those web services

6 Definitions “Web services are loosely coupled software components delivered over Internet standard technologies”  Gartner research, June Informally: web services are like web sites but...  Providing access to all kinds of services, not just documents  For computers rather than people to use

7 Motivations Based on XML messaging Loosely coupled – abstracted service interfaces Use any common programming language Industry standard protocols (HTTP)  Familiar and simple  Internet scope  Firewall compatibility  Established mechanisms for scalability, robustness, etc.

8 Motivations cont. Usable by many types of client Support a range of levels of functionality from trivial to profound Supported by other middleware/platforms  e.g. J2EE, CORBA, Microsoft.NET Support dynamically locatable and invocable services Support cross-platform integration of business applications over the internet

9 Basic Operational Model of Web Services Service Broker Service Provider Service Requestor Discover Service Invoke service Register service

10 Core Web Service Standards Extensible Markup Language (XML)‏  How to encode arbitrary information in document form Simple [Standard] Object Access Protocol (SOAP)‏  How to express web service requests and responses in XML Web Services Definition Language (WSDL)‏  Defines the operations, data types and faults that characterise a web service

11 Core Web Service Standards (cont.)‏ Universal Description, Discovery and Integration (UDDI)‏  How to describe, publish, store and retrieve information about web services in registries WS-Security  Various security-related facilities & definitions, including XML Encryption, XML Key Management System, XML Signature,...

12 Supporting standards TCP/IP  The Internet Protocol suite for reliable global communication DNS – the Domain Name System  The standard Internet naming protocol HyperText Transfer Protocol (HTTP)‏  A common “binding” for SOAP – to carry SOAP requests and responses

13 Basic Operational Model of Web Services w. standards Service Broker Service Provider Service Requestor Discover Service Invoke service Register service Communication: typically SOAP (XML) over HTTP over TCP/IP Optionally secured using WS-Security Interface definition: WSDL (esp. for dynamic invocation)‏ Registry: UDDI & WSDL

14 Other related standards ebXML  Complementary standards specific to e-business Web Services Choreography Interface  Standard(s) for defining more complex patterns of interaction between web services Business Transaction Protocol  Support for web service distributed transactions

15 Challenges for web services Distributed transactions  Coordinated success, failure and recovery Quality of Server (QoS)‏  Reliability and dependability.  Service-level agreements Security  Publicly exposed core business services and operations!

16 Summary Like a WWW for computers  Publishing “services” rather than documents  In XML (for machines) rather than HTML (for people)‏  Using standard technologies (XML, HTTP,...)‏ Especially for  Business-to-business integration and interoperability  Other loosely-coupled distributed applications e.g. bioinformatics