The first architectural principle clarifies whether the Web is used as a publishing medium for delivering application services to clients or as a messaging medium for application integration - in other words, whether HTTP is considered as an application or as a transport protocol.
In the context of REST, the Web is seen as the universal medium for publishing globally accessible information. Applications become part of the Web by using URIs to identify the provided resources, data, and services and by leveraging the full semantics of the four HTTP verbs (GET, POST, PUT, and DELETE) to expose operations on such resources.
Instead, from the perspective of SOAP/WS-*, the Web is seen as the universal transport medium for messages, which are exchanged between Web services endpoints of published applications. Thus, applications gain the ability to remotely interact through the Web but remain ``outside'' of the Web. In other words, the HTTP protocol is used as a tunneling protocol to enable remote communication through firewalls, but it is not used to convey the semantics of the service interaction. This can be seen from the way WS-* uses URIs to address messaging endpoints, which typically remain the same for all operations of a service, whereas REST URIs identify resources of the application domain.
In WS-*, both request and response messages are exchanged using only one HTTP verb (POST), the only one which allows to transfer XML payloads in both directions. This way, the selection of the operation to be performed by the service is no longer done at the HTTP level, but is pushed into the SOAP message7.
The first architectural principle clarifies whether the Web is used as a publishing medium for delivering application services to clients or as a messaging medium for application integration - in other words, whether HTTP is considered as an application or as a transport protocol.
In the context of REST, the Web is seen as the universal medium for publishing globally accessible information. Applications become part of the Web by using URIs to identify the provided resources, data, and services and by leveraging the full semantics of the four HTTP verbs (GET, POST, PUT, and DELETE) to expose operations on such resources.
Instead, from the perspective of SOAP/WS-*, the Web is seen as the universal transport medium for messages, which are exchanged between Web services endpoints of published applications. Thus, applications gain the ability to remotely interact through the Web but remain ``outside'' of the Web. In other words, the HTTP protocol is used as a tunneling protocol to enable remote communication through firewalls, but it is not used to convey the semantics of the service interaction. This can be seen from the way WS-* uses URIs to address messaging endpoints, which typically remain the same for all operations of a service, whereas REST URIs identify resources of the application domain.
In WS-*, both request and response messages are exchanged using only one HTTP verb (POST), the only one which allows to transfer XML payloads in both directions. This way, the selection of the operation to be performed by the service is no longer done at the HTTP level, but is pushed into the SOAP message7.
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