Web Services - Java Data Mining: Strategy, Standard, and Practice - page 267

Figure 11-2 illustrates a Web services architecture with a
discovery service , which finds the appropriate Web service(s)
requested by the requester. When a requester sends a service
request to a discovery service, the service finds the available
provider service, which matches the request criteria and provides
the WSDL associated with the provider to the requester. From the
WSDL specification the requester understands the location of the
provider and semantics for communicating with the provider and
places SOAP requests as discussed in the simple Web services
architecture above.
There are three types of discovery services: registry, index, and
peer-to-peer (P2P). Registry services centrally control the registry of
Web services, where a provider registers in the centrally managed
registry so that it can be discovered by the requester. Index services
do not centrally control the information, rather index services com-
pile information about services and a requester can search there for
appropriate services. P2P allows services to discover each other
dynamically in a network. In P2P, a requester broadcasts service
requirements; peers in the network that satisfy these requirements
respond with the WSDL.
Universal Description, Discovery, and Integration (UDDI) is
accepted as an industry standard for registry services. There are
public Internet UDDI business registries in which one can register
the provider Web services; thus any requester can find via the Inter-
net the available providers for a service. The UDDI registry can be
installed in a private network, so that requesters in the same network
can find available providers.
WSDL, SOAP, and XML Schema are developed by the W3C stan-
dards group; for more details about these technologies refer to
[W3C 2006]. The UDDI standard, other Web services standards such
as the Business Process Execution Language (BPEL), WS-Security,

Discovery
Service 1a-Service

Request

1b-Register Service

1c-WSDL

2-SOAP Requests
3-SOAP Responses

Web Service
Requester

Web Service
Provider

Figure 11-2 Web services architecture with Discovery Service.