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Blogged date : 2005 Jan 10
What is Web Services
A Web service is a software application identified by a URI, whose interfaces and binding are capable of being defined, described and discovered by XML artifacts and supports direct interactions with other software applications using XML based messages via internet-based protocols.
When a web service is created, it registered itself to a service registry. By registering in the service registry, the Web service exposes its interface to any client that is interested in accessing it.
When a client requires a certain service, it first looks in the service registry, this is the service discovery phase.
Once an appropriate web service has been located, the client then invokes the web services, which delivers the service to the client.
Core Web Services Standards
The Universal Description, Discovery, and Integration standard provides a mechanism for business to "describe" themselvs and the types of services they provide and then register and publish themselvs in a UDDI Registry. Such published businesses can be searched for, queried, or "discovered" by other business using SOAP messages.
What is SOAP
SOAP, Simple Object Access Protocol is a wire protocol which defines data encoding. In other words, it specifies rules of how data types get serialized over the wire.
SOAP message is made of SOAP Envelope and zero or more attachments. The SOAP Envelope in turn is then made of header and body. SOAP attachment allows the SOAP message to contain not only the XML data but also non-XML data such as binary graphics file. And it uses the MIME multipart as container for these non-XML data.
What is WSDL
WSDL is industry-agreed-upon XML language that can be used to describe web services. Under WSDL, a Web service is described as a set of communication endpoints that are capable of exchanging messages. These communication endpoints are called ports.
An endpoint is made of two parts:
Abstract definitions of operations and messages which are related in that messages are exchanged for the purpose of performing the operations.
Concrete binding of those abstract definitions of operations to concrete network protocol and message format.
WSDL specification defines 7 element types
Types element define data types such as string or integer or custom data type which are used to describe the messages being exchanged.
Message element define abstract and typed definitions of data being exchanged.
Operation is an abstract description of an action which is made of input and/or output messages defined using message elements.
Port type element is just a collection of operations.
Binding element specifies the binding of a port type, which is a collection of abstract operations, to a concrete transport protocol and data format.
Service is a set of communication endpoints which are called as ports.
Port element defines an address for transport protocol that was selected for binding.
Port element defines an address for transport protocol that was selected for binding.
What is UDDI
The Universal Description, Discovery, and Integration standard provides a mechanism for business to "describe" themselves and the types of services they provide and then register and publish themselves in a UDDI Registry.
The information contained in the business registration data can be categorized into:
White pages contains information on a particular business entity, for example, name, contact information, address, or unique identification number.
Yellow pages contains categorization information according to industry, product and service, or geographic location.
Green pages contains so-called information about the service which is basically meta information on services and this meta information has references to service definitions represented by WSDL document.
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