Web services: Why and How OOPSLA 2001 F. Curbera, W.Nagy, S.Weerawarana Nclab, Jungsook Kim

Paper summary The Objective of this paper  Introduce why Web services is needed and What is the requirements for the Web services

Contents Paper Summary Why Web services? What is needed for Web services? Discussion: Pros and cons What is a Web service? A Web Service framework

Why Web services? A natural consequence of the evolution of the Web  Medium to enable Human-to-application  Medium to enable application-to-application Automated business-to-business transactions Large-scale resource sharing

Isn’t there any architecture for application-to-application before Web services? Existed, but traditional distributed architecture is not universally interoperable  Web is everywhere and accessible anywhere Traditional distributed architectures for application-to- application interaction  J2EE Purely java-based mechanism  CORBA IIOP, CORBA's transport protocol is not particularly firewall friendly requires an elaborate infrastructure like a CORBA ORB

What is needed for Web services? Nature of the Web  very heterogeneous distributed system  Open and dynamic Requirements reflecting the above features for Web services  Define a minimum set of standards to assure basic interoperability at the information exchange level SOAP protocol  Use already existing standards  XML  extremely simple  Just a few conventions on how to construct headers and body in an XML message  Declared to be transport independent

What is needed for Web services?  Provide a unified view of applications within heterogeneous systems WSDL  Separate abstract application descriptions from protocol binding  Abstract application description  Data types  Messages  Application interfaces as collections of operations  A application can select best protocol bindings.  A single application can provide multiple protocol bindings

What is needed for Web services?  Provide Service register UDDI  Application developers find services and develop code that relies on those services  Just-in-time integration of service components  Provide Service composition WSFL, XLANG, BPEL4WS  A process of assembling service components to create new services

Discussion What is the advantages and problems of the Web services?

Discussion Advantages  Interoperability Any Web service can interact with any other Web services  Ubiquity Any device which supports standard protocols can both host and access Web services  Just-In-time Integration Collaborations in Web services are bound dynamically at runtime  Extension of Legacy Applications Generate a SOAP wrapper and cast the application as a Web service

Discussion Advantages  Easy Learning Curve Concept is easy Web services reduce complexity through encapsulation  Industry Support Free toolkits from vendors like IBM, MS, Sun

Discussion Challenges and Problems  Reliability HTTP widespreadly used transport protocol for Web services is a best effort delivery service HTTPR, BEEP, DIME  Widespread adoption will take time Messaging queuing  Cost of response time  Security

Discussion Challenges and Problems  Transaction Traditional transaction system using two-phase commit approach dose not work well  May not support or allow locking  costly  Scalability Additional load requires additional resources rather than extensive modification of the application itself

Discussion Challenges and Problems  Performance SOAP is degraded because of the following  SOAP uses XML instead of binary data which makes the size of the data almost 400% larger  Parsing the XML information in the SOAP envelop is time- expensive  Encoding binary data in a form acceptable to XML is time- expensive  XML parsers supports a number of features which makes them resource intensive. Not all of these features may be used by SOAP  Pricing model Difficult to build charging model

Thank you

What is a Web service A network application that is able to interact using standard Web protocols over well defined interfaces and which is described using a standard functional description language Characteristics of Web services  Gray box component  Loosely coupled interaction model  Flexible interaction  Message instead of APIs

A Web services Framework Service Oriented Architecture Service Provider Service Requester Service Broker Bind Find Publish

A Web services Framework SOAP – Simple Object Access Protocol  An XML protocol to invoke a method on a server to execute  A requested operation and get a response in XML  Request message is sent by service requester  Response message I sent by service provider UDDI – Universal Description, Discovery, Integration  UDDI servers act as a directory of available services and service providers  SOAP can be used to query UDDI for services WSDL – Web Services Description Languages  An XML vocabulary to describe service interfaces