Web services#

What are web services?#

A web service is a software function that is hosted at a network addressable location. IBM

Distributed systems rely on web services.

What they solve?#

Web services attempt to solve some of the problems presented by other distributed systems development technologies:

• Complexity: High learning curve.
  • Solution: Web services are easy to learn.
• Interoperability: Different implementation languages.
  • Solution: Web services are platform-independent.
• Firewall: Need to configure the non-standard ports to be used.
  • Solution: Web services use only standard ports, because they use HTTP (port 80) or HTTPS (port 443) protocol, which are standard ports.

Architecture#

Web services follows Client-Server pattern.

Views#

Conceptual#

• Software component accesible through network.
• Both clients and services send requests and responses—respectively—via messages.
• They make no assumptions about the technological characteristics of the receiver.

Technological#

They are two main approaches:

• SOAP service: Offers an arbitrary set of operations. (Complex)
• REST service: Manipulate representations of web resources using a uniform set of stateless operations. (Simple)

SOAP vs. REST#

SOAP#

SOAP is a protocol for information exchange in a decentralized and distributed environment.

Defines a message architecture and its formats in XML. The language is WSDL.

WSDL#

• XML format for interface operations, parameters, messages and response type.
• Contract between the server and the client: what should the request and response messages contain.
• Declare where the service is.
• What protocol will be used.

WSDL examples here.

REST#

REST services are viewed as resources and may be invoked with an URI.

Consider HTTP not only as a transport protocol, but also as an API.

More about REST here.