2.4.1 The Interface Operation
Component
An Interface
Operation component describes an operation that a given
interface supports. An operation is an interaction with the service
consisting of a set of (ordinary and fault) messages exchanged
between the service and the other parties involved in the
interaction. The sequencing and cardinality of the messages
involved in a particular interaction is governed by the message
exchange pattern used by the operation (see {message
exchange pattern} property).
A message exchange pattern defines placeholders for messages,
the participants in the pattern (i.e., the sources and sinks of the
messages), and the cardinality and sequencing of messages exchanged
by the participants. The message placeholders are associated with
specific message types by the operation that uses the pattern by
means of message and fault references (see {interface
message references} and {interface
fault references} properties). The service whose operation is
using the pattern becomes one of the participants of the pattern.
This specification does not define a machine understandable
language for defining message exchange patterns, nor does it define
any specific patterns. The companion specification, [WSDL 2.0 Adjuncts] defines a set of such
patterns and defines identifying IRIs any of which MAY be used as
the value of the {message
exchange pattern} property.
The properties of the Interface Operation component
are as follows:
For each Interface
Operation component in the {interface operations}
property of an Interface
component, the {name} property MUST be
unique. Note that this constraint is enforced by the normative WSDL
2.0 XML schema.
Interface Operation
components are uniquely identified by the QName of the enclosing
Interface component and QName of
the Interface Operation
component itself.
In
cases where, due to an interface extending one or more other
interfaces, two or more Interface Operation components
have the same value for their {name} property, then the
component models of those Interface Operation components MUST be
equivalent (see 2.15 Equivalence of
Components).†
If the Interface
Operation components are equivalent then they are considered to
collapse into a single component. Within the same Interface component, if two Interface Operation components
are not equivalent then their {name} properties MUST NOT
be equal.
Note that, due to the above rules, if two interfaces that have
the same value for the namespace name of their {name} property also have one or more
operations that have the same value for their {name} property, then those
two interfaces cannot both form part of the derivation chain of a
derived interface unless those operations are the same
operation.
For
the above reason, it is considered good practice to ensure, where
necessary, that the {name} property of Interface Operation components
within a namespace SHOULD be unique, thus allowing such derivation
to occur without inadvertent error.†
More than one Interface Fault Reference
component in the {interface
fault references} property of an Interface Operation component
may refer to the same message label. In that case, the listed fault
types define alternative fault messages. This allows one to
indicate that there is more than one type of fault that is related
to that message.
2.4.1.1 Message Exchange Pattern
This section describes some aspects of message exchange patterns
in more detail. Refer to the Web Services Description Language
(WSDL) Version 2.0 Part 2: Adjuncts specification
[WSDL 2.0 Adjuncts] for a
complete discussion of the semantics of message exchange patterns
in general, as well as the definitions of the message exchange
patterns that are predefined by WSDL 2.0.
A placeholder message is a template for an actual
message as described by an Interface Message
Reference component. Although a placeholder message is not
itself a component, it is useful to regard it as having both a
{message
label} and a {direction}
property which define the values of the actual Interface Message
Reference component that corresponds to it. A placeholder
message is also associated with some node that exchanges the
message with the service. Furthermore, a placeholder message may be
designated as optional in the exchange.
A fault propagation ruleset specifies the relation
between the Interface
Fault Reference and Interface Message
Reference components of an Interface Operation component.
The Web Services Description Language (WSDL) Version 2.0 Part
2: Adjuncts specification [WSDL
2.0 Adjuncts] defines three fault propagation rulesets
which we will refer to as fault-replaces-message,
message-triggers-fault, and no-faults. These
three fault propagation rulesets are used by the predefined message
exchange patterns defined in [WSDL 2.0
Adjuncts]. Other message exchange patterns can define
additional fault propagation rulesets.
A message exchange pattern is a template for the
exchange of one or more messages, and their associated faults,
between the service and one or more other nodes as described by an
Interface Operation
component. The service and the other nodes are referred to as the
participants in the exchange. More specifically, a message
exchange pattern consists of a sequence of one or more placeholder
messages. Each placeholder message within this sequence is uniquely
identified by its {message
label} property. A message exchange pattern is itself uniquely
identified by an absolute IRI, which is used as the value of the
{message
exchange pattern} property of the Interface Operation component,
and which specifies the fault propagation ruleset that its faults
obey.†
2.4.1.2 Operation Style
An operation style specifies additional information about an
operation. For example, an operation style may define structural
constraints on the element declarations of the interface message
reference or interface fault components used by the operation. This
additional information in no way affects the messages and faults
exchanged with the service and it can therefore be safely ignored
in that context. However, the additional information can be used
for other purposes, for example, improved code generation. The
{style} property
of the Interface
Operation component contains a set of zero or more IRIs that
identify operation styles. An Interface Operation component
MUST satisfy the specification defined by each operation style
identified by its {style} property.
†
If no Interface
Operation component can simultaneously satisfy all of the
styles, the document is invalid.
If the {style}
property of an Interface
Operation component does have a value, then that value (a set
of IRIs) specifies the rules that were used to define the element
declarations (or other properties that define the message and fault
contents; see 3.2 Using Other Schema
Languages) of the Interface Message
Reference or Interface
Fault components used by the operation. Although a given
operation style has the ability to constrain all input and
output messages and faults of an operation, it MAY choose to
constrain any combination thereof, e.g. only the messages, or only
the inputs.
Please refer to the Web Services Description Language (WSDL)
Version 2.0 Part 2: Adjuncts specification [WSDL 2.0 Adjuncts] for particular
operation style definitions.
2.4.2 XML Representation of
Interface Operation Component
<description>
<interface>
<operation
name="xs:NCName"
pattern="xs:anyURI"?
style="list of xs:anyURI"? >
<documentation />*
[ <input /> | <output /> | <infault /> | <outfault /> ]*
</operation>
</interface>
</description>
The XML representation for an Interface Operation component
is an element information item with the following Infoset
properties:
-
A [local name] of operation
-
A [namespace name] of "http://www.w3.org/ns/wsdl"
-
Two or more attribute information items amongst its
[attributes] as follows:
-
One or more element information item amongst its
[children], in order, as follows:
-
Zero or more documentation element information
items (see 5.
Documentation).
-
One or more element information items from among the
following, in any order:
-
One or more element information items from among the
following, in any order:
-
Zero or more namespace-qualified element information
items whose [namespace name] is NOT
"http://www.w3.org/ns/wsdl".
2.4.2.1 name
attribute information item with operation
[owner element]
The name attribute information item
identifies a given operation element information
item inside a given interface element
information item.
The name attribute information item has
the following Infoset properties:
The type of the name attribute information
item is xs:NCName.
2.4.2.2
pattern attribute information item with
operation [owner element]
The pattern attribute information item
identifies the message exchange pattern a given operation uses.
The pattern attribute information item has
the following Infoset properties:
The type of the pattern attribute information
item is xs:anyURI. Note that its value must be an
absolute IRI (see [IETF RFC
3987]).
2.4.2.3 style
attribute information item with operation
[owner element]
The style attribute information item
indicates the rules that were used to construct the {element
declaration} properties of the Interface Message
Reference components which are members of the {interface
message references} property of the [owner element]
operation.
The style attribute information item has
the following Infoset properties:
The type of the style attribute information
item is list of xs:anyURI. Note that its value must
be an absolute IRI (see [IETF RFC
3987]).