Web services

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Web services

• A Web service is an interface that describes a
  collection of operations that are
  network-accessible through standardized XML
  messaging.
• A Web service is described using a
  standard,formal XML notion,called its service
  description.
• The service description contains the details of
  the interface and implementation of the
  service.This includes its data types,operations,bi
  nding information and network location. It could
  also include categorization and other meta-data
  to facilitate discovery and utilization by
  service requestors.The service description might
  be published to a service requestor or to a
  service registry.

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Service description

• covers all the details necessary to interact with
  the service,including message formats (that
  detail the operations),transport protocols and
  location.
• The interface hides the implementation details of
  the service, allowing it to be used independently
  of the hardware or software platform on which it
  is implemented and also independently of the
  programming language in which it is written.
• Allows and encourages Web Services-based
  applications to be loosely coupled,component-orien
  ted, cross-technology implementations.
• Web services can be used alone or with other Web
  Services to carry out a complex aggregation or a
  business transaction.

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Web services model
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Using WSDL Web services description language

• A service provider describes its service using
  WSDL. This definition is published to a directory
  of services. The directory could use Universal
  Description, Discovery, and Integration (UDDI).
  Other forms of directories can also be used.
• A service consumer issues one or more queries to
  the directory to locate a service and determine
  how to communicate with that service. 
• Part of the WSDL provided by the service provider
  is passed to the service consumer. This tells the
  service consumer what the requests and responses
  are for the service provider.
• The service consumer uses the WSDL to send a
  request to the service provider.
• The service provider provides the expected
  response to the service consumer.

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UDDIUniversal Description, Discovery, and
Integration

• The UDDI registry is intended to eventually serve
  as a means of "discovering" Web Services
  described using WSDL . The idea is that the UDDI
  registry can be searched in various ways to
  obtain contact information and the Web Services
  available for various organizations.
• How much "discovery" will be used in the early
  days of Web Services is open to discussion.
• Nevertheless, even without the discovery portion,
  the UDDI registry is a way to keep up-to-date on
  the Web Services your organization currently
  uses.

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SOAP

• All the messages shown in the above figure are
  sent using SOAP. (SOAP at one time stood for
  Simple Object Access Protocol. Now, the letters
  in the acronym have no particular meaning .)
• SOAP essentially provides the envelope for
  sending the Web Services messages.
• SOAP generally uses HTTP , but other means of
  connection may be used. HTTP is the familiar
  connection we all use for the Internet. In fact,
  it is the pervasiveness of HTTP connections that
  will help drive the adoption of Web Services.
• It is the standardized enveloping mechanism for
  communicating document-centric messages and
  remote procedure calls using XML
• SOAP messages support the publish, find and bind
  operations in the Web Services architecture.

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Simplified Web Services notation
Service producer could also be a service
consumer