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Jaggan Nalangilli [email protected] A Web service is a collection of protocols and standards used for exchanging data between applications or systems. Enables re-usability of applications. Connects two applications following different protocols or standards. Examples: Amazon Simple Storage Service which offers an interface to store and retrieve data anytime. Web services use commonly used protocols like HTTP which are not blocked by firewalls. Representation State Transfer (REST) Simple Object Access Protocol (SOAP) Described by Roy Fielding in his PhD dissertation. Based on the concept of transferring state between two systems on a network. Similar to architecture of the web. ◦ Already familiar to most users. So, more popular. Data is identified by Uniform Resource Identifier (URI). HTTP verbs like GET, POST, DELETE are used to issue requests to a REST web service. Client-server interaction system Stateless No central store of information. This leads to faster recovery in case of failure. ◦ All requests must have all information to understand the complete request. ◦ Increases reliability. Highly scalable as it is based on the web which has proved to be extremely scalable. ◦ Less memory is required to store state information. Formal and standardized approach of W3C. Based on XML Built-in support for extensions of the stack for more complex applications. Can use any network protocol. SOAP messages have an envelope consisting of header and body. Header contains control information. Can add extensible information. Body contains actual message. SOAP is a standardized protocol and offers more opportunities for extensibility. REST supporter feel custom-defined webservice interfaces do not automatically result in scalability or reliability. They also believe that security problems will plague SOAP. SOAP supporters feel that QoS is addressed very superficially in REST. According to SOAP the web is just a platform for carrying SOAP messages from the source to destination. SOAP is designed to run over any protocol. REST views the web as a scalable information system. REST is usually preferred in areas with intense queries where large quantities of data need to exchanged. SOAP is preferred wherever different levels of QoS are required and state information need to be maintained. Many companies like MS and IBM support SOAP. Some like yahoo offer only in REST. When both are available, users tend to prefer REST. This can be because of familiarity with the web on which it is based. Amazon supports both SOAP and REST. 85% of developers using Amazon Web Services use REST.