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• Message Triggers Fault—any message, including the first in the pattern, may trigger a fault message, which must have opposite direction and be delivered to the originator of the
triggering message • No Faults—faults must not be propagated
pattern=http:www.w3.orgnswsdlin-out This line specifies that this operation will use the in-out pattern as described above. WSDL 2.0 uses URIs to identify message exchange patterns in
order to ensure that the identifiers are globally unambiguous, while also permitting future new patterns to be defined by anyone. However, just because someone defines a new pattern and
creates a URI to identify it, that does not mean that other WSDL 2.0 processors will automatically recognize or understand this pattern. As with any other extension, it can only be used among
processors that do recognize and understand it.
8.3.3 Binding a Web Service Implementation
Several service providers may implement the same abstract interface.
Client Service
input
In-Only no faults
Client Service
input
Robust In-Only message triggers fault
Client Service
output Out-Only no faults
Client Service
output Robust Out-Only message triggers fault
Client Service
output input
Out-In fault replaces message
Client Service
output
Out-Optional-In message triggers fault
Client Service
input output
In-Out fault replaces message
Client Service
input
In-Optional-Out message triggers fault
A one-way operation:
A request-response operation: A notification operation:
A solicit-response operation:
output
opt
input
opt
c
d c
c c
c c
c c
d
d d
Figure 8-13: WSDL Message Exchange Patterns MEPs with their fault propagation rules.
Ivan Marsic • Rutgers University
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Figure 8-14 Service
Each endpoint must also reference a previously defined binding to indicate what protocols and transmission formats are to be used at that endpoint. A service is only permitted to have one
interface .
Figure 8-15 port describes how a binding is deployed at a particular network endpoint
8.3.4 Using WSDL to Generate SOAP Binding
Developers can implement Web services logic within their applications by incorporating available Web services without having to build new applications from scratch. The mechanism
that makes this possible is the Proxy design pattern, which is described in Section 5.2.2 above and already employed for distributed computing in Section 5.4. Proxy classes enable developers to
reference remote Web services and use their functionality within a local application as if the data the services return was generated in the local memory space.
Figure 8-16 illustrates how WSDL is used to generate WSDL Web service description from the Web-service’s interface class. Given the WSDL document, both client- and server side use it to
wsdl: BindingOperationType
outfault infault
output input
∗
ref other:any
wsdl: BindingType
operation wsdl:
binding wsdl:
binding
∗
fault other:any
type name
?
interface
Figure 8-14: The XML schema for WSDL 2.0 binding element.
wsdl: EndpointType
∗
wsdl: ServiceType
wsdl: service
wsdl: service
+
other:any
interface name
?
endpoint other:any
other:any other:any
binding name
address
Figure 8-15: The XML schema for WSDL 2.0 service element.
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generate the stub and skeleton proxies, respectively. These proxies interact with the SOAP-based middleware.
WSDL code generator tools one of which is reviewed in Section 8.5 below allow automatic generation of Web services, automatic generation of WSDL documents, and invocation of Web
services.
8.3.5 Non-functional Descriptions and Beyond WSDL
WDSL only describes functional characteristics of a particular Web service how to invoke it. But this is only part of the picture and will be sufficient only for standalone Web services that will be
used individually. In some cases, non-functional characteristics such as performance, security, reliability may be important, as well. In a general case, the service consumer needs to know:
• How to invoke the service? supported by WSDL, described above
• What are the characteristics of the service? not supported by WSDL -
Is a service more secure than the others are? -
Does a particular provider guarantee a faster response or a more scalable and reliableavailable service?
- If there is a fee for the service, how does billing and payment processing work?
Service requestor Service provider
WSDL document of service provider
Application object client
SOAP-based middleware
Stub Application object
Web service
SOAP-based middleware
Skeleton
1 3
2
WSDL compiler client side
WSDL compiler server side
WSDL generator
Figure 8-16: From a Programming Interface to WSDL and back to the Program: Step n: generate WSDL documents from interface classes or APIs.
Step o: generate server-side stub from the WSDL document. Step p: generate client-side stub from the WSDL document.
