What's New in WSDL 2.0
by Arulazi Dhesiaseelan
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Import
The concept behind the import element is very similar to
that of include element, except that the imported WSDL can
be in different target namespaces. The namespace attribute
for the import element is mandatory while the
location attribute is optional. Figure 4 shows the XML
schema for the import element.
Figure 4: import schema
Types
The types element defines the data types used by the
exchanged messages. WSDL uses W3C XML Schema as its preferred
schema language. It also supports other systems such as DTDs and
RELAX NG. Schemas may be used by importing or embedding within the
types element of the WSDL document. Importing can be done
using the construct xs:import while embedding uses the
construct xs:schema. The imported or embedded schema
components are available to WSDL for reference by QName. Figure 5
shows the XML schema for the types element.
Figure 5: types schema
Interface
An interface element encloses a named set of abstract
operations and the abstract messages. It can optionally extend one
or more other interfaces. Interfaces are referred to by QName in
other components such as bindings. The interface operation
element has name and pattern as required attributes, while style is
an optional attribute. Figure 6 shows the schema for the
interface element. Features defines functionalities
associated with the message exchanges between communicating
parties, which might include reliability, security, correlation,
and routing. Property is used to control the behavior of a feature.
It has a set of possible and permissible values specified by
references to a schema description. These values can be shared
among features.
Figure 6: interface schema
Binding
The binding element defines the underlying transport and
wire format for messages. Each binding in the WSDL references to an
interface. All operations defined within the interface must be bound
in the binding. An endpoint in the service component references a
binding. Both endpoints and bindings are modeled to support
flexibility and location transparency. Multiple endpoints with
different network address can still share the same protocol
binding. WSDL 2.0 Bindings specification defines binding extensions
for protocols and message formats such as SOAP, HTTP and MIME. Figure
7 shows the XML schema for the binding element.
Figure 7: binding schema
Service
A service element describes a set of endpoints which
refer to a single network address for a binding. All other protocol
specific information is contained in the binding. Service can be
referred by QName. service element has a name and
interface which are required attributes. Figure 8 shows the
XML schema for the service element.
Figure 8: service schema
WSDL Message Exchange Patterns
Message exchange patterns define the sequence and cardinality of
messages within an operation. Several types of message patterns are
defined in the “Part 2: Message
Patterns†of the WSDL 2.0 specifications. WSDL message
exchange patterns uses fault generation rules to indicate the
occurrence of faults. Message exchange may be terminated if fault
generation happens regardless of standard rule sets. The following
standard rule set outlines the behavior of fault generation.
-
Fault Replaces Messages
-
Message Triggers Fault
-
No Faults
Figure 9 shows the various message exchange patterns with their
fault reference rules.
Figure 9: WSDL Message Exchange Patterns
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