elektronická verzia publikácie - FIIT STU - Slovenská technická ...

170 Selected Studies on Software and Information Systems
”A Web service is a software system identified by a URI, whose public interfaces
and bindings are defined and described using XML. Its definition can be discovered
by other software systems. These systems may then interact with the Web
service in a manner prescribed by its definition, using XML based messages
conveyed by Internet protocols.”
Web services are one of the implementations of SOA. They play an important role in B2B
(business-to-business) integration. It is assumed that the companies will expose the functionality
they offer as a service. It means that they will publish an interface via which this
service can be invoked. The invocation is done by a program. Thus, requesting and executing
a service involves a program calling another program. There occur confusions because there
are a lot of services available through the Web which are not web services. An example is
a fly ticket booking system. A web service is a software application with a published a stable
programming interface, not a set of Web pages.
Web services are used to make some utility available through the Web. They wrap
a functionality of an internal system and make it available for other applications, see Figure
6-2. Web services are developed as loosely coupled application components using any
programming language, any protocol, and any platform.
internal
service
middleware
Company A (provider)
Web
service
Web
service
Web
service
internal
service
wide area network (Internet)
client
internal
service
middleware
Company B (client)
internal
service
Figure 6-2. Web services provide an entry point for accessing local services (retrieved from [3]).
The web service framework is divided into three areas [28]:
– the simple object access protocol (SOAP, www.w3.org/TR/soap/) which enables communication
among Web services,
– Web Services Description Language (WSDL, www.w3.org/TR/wsdl.html), which provides
a formal, computer-readable description of Web services,
– Universal Description, Discovery, and Integration (UDDI, www.uddi.org) directory,
which is a registry of Web services descriptions.