- It is designed to support interoperable applications to application / machine-to-machine interaction. Web services are self-contained business functions that operate over the Internet.
- Web Service is defined by the World Wide Web Consortium (W3C). It provides an interface for a service oriented architecture (SOA), in which Web-based applications dynamically interact with other Web applications using open standards that include XML running over HTTP, UDDI, and SOAP.
- These are services made available from a business’s Web server for Web users or other Web-connected programs.
- Web services is Internet or other IP-based network applications built with four emerging standards: XML, simple object access protocol (SOAP), Web services description language (WSDL), and universal description discovery and integration (UDDI).
Web Services Architecture
1 It represents a service provider publishing a service to an external repository. Once such a service has been exported to a registry, it can then be used by a client.
2 and 3 represent looking up a service from a repository and returning information about a service, respectively. Information, such as the format of the procedure calls and the address of a service provider, would normally be provided, amongst other details.
4 and 5 represent the client binding to an underlying service and then accessing that service to use whatever functionality the service provides.
Advantages
Data is formatted for transfer using XML, improving or eliminating marshalling, unmarshalling, and various other translation-related requirements normally coded by a developer.
Data is passed using standardized protocols such as HTTP or SMTP, which have published well-defined standards.
The underlying exposed service is well-defined using a known accepted mechanism, WSDL.
Services are found using a well-defined standard, UDDI, and the more advanced ebXML.
A Simple Web Service
SOAP (Simple Object Access Protocol):
- Application Level protocol.
- Consists of Envelope, which in turn consists of Header and Body.
- Lightweight protocol for exchange of information in a decentralized, distributed environment.
- XML based protocol that consists of three parts:
- an envelope that defines a framework for describing what is in a message and how to process it,
- a set of encoding rules for expressing instances of application-defined data types,
- and a convention for representing remote procedure calls and responses.
WSDL(Web Services Description Language):
- WSDL – Web Services Description Language
- WSDL defines the syntax, the semantics, and all the various administrative aspects of a Web Services procedure call
- WSDL uses XML Schema to specify the types
