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Web Services Addressing provides transport-neutral mechanisms to address Web services and messages. Web Services Addressing 1.0 - Core (this document) defines an XML Infoset [XML Information Set] to reference Web services and to facilitate end-to-end addressing of endpoints in messages. This specification enables messaging systems to support message transmission through networks that include processing nodes such as endpoint managers, firewalls, and gateways in a transport-neutral manner.
This document is an editors' copy that has no official standing.
1. Introduction
1.1 Notational Conventions
1.2 Namespaces
2. Endpoint References
2.1 Endpoint Reference Representation
2.2 Endpoint Reference Comparison
2.3 Endpoint Reference Lifecycle
2.4 Endpoint Reference Extensibility
3. Message Addressing Properties
3.1 Representation of Message Addressing Properties
3.1.1 Comparing IRIs
3.2 Formulating a Reply Message
4. Security Considerations
5. References
A. Acknowledgements (Non-Normative)
B. Change Log (Non-Normative)
B.1 Changes Since Last Call Working Draft
B.2 Changes Since Second Working Draft
B.3 Changes Since First Working Draft
B.4 Changes Since Submission
Web Services Addressing 1.0 - Core (WS-Addressing) defines two constructs, message addressing properties and endpoint references, that normalize the information typically provided by transport protocols and messaging systems in a way that is independent of any particular transport or messaging system.
A Web service endpoint is a (referenceable) entity, processor, or resource to which Web service messages can be addressed. Endpoint references convey the information needed to address a Web service endpoint.
This specification defines a family of message addressing properties that convey end-to-end message characteristics including references for source and destination endpoints and message identity that allows uniform addressing of messages independent of the underlying transport.
Both of these constructs are designed to be extensible and re-usable so that other specifications can build on and leverage endpoint references and message addressing properties.
The following example illustrates the use of these mechanisms in a SOAP 1.2 message being sent from http://example.com/business/client1 to http://example.com/fabrikam/Purchasing (see Web Services Addressing 1.0 - SOAP Binding[WS-Addressing-SOAP] for more information on the use of WS-Addressing in SOAP):
Example 1-1. Use of message addressing properties in a SOAP 1.2 message.
(01) <S:Envelope xmlns:S="http://www.w3.org/2003/05/soap-envelope"
xmlns:wsa="http://www.w3.org/@@@@/@@/addressing">
(02) <S:Header>
(03) <wsa:MessageID>http://example.com/6B29FC40-CA47-1067-B31D-00DD010662DA</wsa:MessageID>
(04) <wsa:ReplyTo>
(05) <wsa:Address>http://example.com/business/client1</wsa:Address>
(06) </wsa:ReplyTo>
(07) <wsa:To>http://example.com/fabrikam/Purchasing</wsa:To>
(08) <wsa:Action>http://example.com/fabrikam/SubmitPO</wsa:Action>
(09) </S:Header>
(10) <S:Body>
(11) ...
(12) </S:Body>
(13) </S:Envelope>
Lines (02) to (09) represent the header of the SOAP message where the mechanisms defined in the specification are used. The body is represented by lines (10) to (12).
Lines (03) to (08) contain the message addressing header blocks. Specifically, line (02) specifies the identifier for this message and lines (04) to (06) specify the endpoint to which replies to this message should be sent as an endpoint reference. Line (07) specifies the address URI of the ultimate receiver of this message. Line (08) specifies an action URI identifying expected semantics.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [IETF RFC 2119].
When describing concrete XML schemas [XML Schema Structures, XML Schema Datatypes], this specification uses the notational convention of WS-Security [WS-Security]. Specifically, each member of an Element Information Item's [children] or [attributes] property is described using an XPath-like notation (e.g., /x:MyHeader/x:SomeProperty/@value1). The use of {any} indicates the presence of an element wildcard (<xs:any/>). The use of @{any} indicates the presence of an attribute wildcard (<xs:anyAttribute/>). In addition, where pseudo-schemas are provided for a component, they use BNF-style conventions for attributes and elements: "?" denotes optionality (i.e. zero or one occurrences), "*" denotes zero or more occurrences, "+" one or more occurrences, "[" and "]" are used to form groups, and "|" represents choice. Attributes are conventionally assigned a value which corresponds to their type, as defined in the normative schema. Elements with simple content are conventionally assigned a value which corresponds to the type of their content, as defined in the normative schema.
This specification uses a number of namespace prefixes throughout; they are listed in Table 1-1. Note that the choice of any namespace prefix is arbitrary and not semantically significant (see [XML Namespaces]).
| Prefix | Namespace |
|---|---|
| S | http://www.w3.org/2003/05/soap-envelope |
| wsa | http://www.w3.org/@@@@/@@/addressing |
| xs | http://www.w3.org/2001/XMLSchema |
WS-Addressing may be used with SOAP [SOAP 1.2 Part 1: Messaging Framework, SOAP 1.1] as described in Web Services Addressing 1.0 - SOAP Binding[WS-Addressing-SOAP]. WS-Addressing may be used with WSDL [WSDL 2.0, WSDL 1.1] described services as described in Web Services Addressing 1.0 - WSDL Binding[WS-Addressing-WSDL]. Examples in this specification use an XML 1.0 [XML 1.0] representation but this is not a requirement.
All information items defined by this specification are identified by the XML namespace URI [XML Namespaces] http://www.w3.org/@@@@/@@/addressing. A normative XML Schema [XML Schema Structures, XML Schema Datatypes] document can be obtained by dereferencing the XML namespace URI.
This section defines the information model and syntax of an endpoint reference.
This specification introduces the endpoint reference, a construct designed to support the following usage scenarios:
Dynamic generation and customization of service endpoint descriptions.
Referencing and description of specific service instances that are created as the result of stateful interactions.
Flexible and dynamic exchange of endpoint information in tightly coupled environments where communicating parties share a set of common assumptions about specific policies or protocols that are used during the interaction.
This section defines the XML Infoset-based representation for an endpoint reference as both an XML type (wsa:EndpointReferenceType) and as an XML element (<wsa:EndpointReference>). For brevity simple XML terms are used, e.g. 'element' instead of 'element information item' - this is not intended to constrain use of the constructs defined in this section to textual XML representations.
The wsa:EndpointReferenceType type is used wherever a Web service endpoint is referenced. The following describes the contents of this type:
<wsa:EndpointReference>
<wsa:Address>xs:anyURI</wsa:Address>
<wsa:ReferenceParameters>xs:any*</wsa:ReferenceParameters> ?
<wsa:Metadata>xs:any*</wsa:Metadata>?
</wsa:EndpointReference>The following describes the attributes and elements listed in the schema overview above:
This represents some element of type wsa:EndpointReferenceType. This example uses the predefined <wsa:EndpointReference> element, but any element of type wsa:EndpointReferenceType may be used.
An absolute IRI representing the address of the endpoint.
This is a REQUIRED element whose content is of type xs:anyURI property of the endpoint reference.
This is an extensibility mechanism to allow additional attributes to be specified.
A reference may contain a number of individual parameters which are associated with the endpoint to facilitate a particular interaction. Reference parameters are namespace-qualified element information items that are required to properly interact with the endpoint. Reference parameters are provided by the issuer of the endpoint reference and are assumed to be opaque to other users of an endpoint refernce. The binding of reference parameters to messages depends upon the protocol binding used to interact with the endpoint - Web Services Addressing 1.0 - SOAP Binding[WS-Addressing-SOAP] describes the default binding for the SOAP protocol.
This OPTIONAL element may contain elements (individual parameters) from any namespace.
This is an extensibility mechanism to allow additional attributes to be specified.
Each element (including all of that element's [children], [attributes] and [in-scope namespaces]) that is a child of /wsa:EndpontReference/wsa:ReferenceParameters represents an individual reference parameter.
This OPTIONAL element may contain elements from any namespace. Such elements form the metadata that is relevant to the interaction with the endpoint.
A reference may contain metadata that describes the behavior, policies and capabilities of the endpoint. Metadata may be included in an endpoint reference to facilitate easier processing by a user of an endpoint reference, or because the metadata was dynamically generated.
The metadata embedded in an EPR is not necessarily a complete statement of the metadata pertaining to the endpoint. Moreover, while embedded metadata is necessarily valid at the time the EPR is initially created it may become stale at a later point in time.
To deal with conflicts between the embedded metadata of two EPRs that have the same [address], or between embedded metadata and metadata obtained from a different source, or to ascertain the current validity of embedded metadata, mechanisms that are outside of the scope of this specification, such as EPR life cycle information (see 2.3 Endpoint Reference Lifecycle) or retrieval of metadata from an authoritative source, SHOULD be used.
Each child element of Metadata represents an individual piece of metadata.
This is an extensibility mechanism to allow additional attributes to be specified. Some examples in this specification show use of this extensibility point to include a wsdlLocation[WSDL 2.0] attribute to provide a hint for the location of a WSDL description of the service deployed at the endpoint.
This is an extensibility mechanism to allow additional elements to be specified.
This is an extensibility mechanism to allow additional attributes to be specified.
The following shows an example endpoint reference. This element references the the endpoint at the URI "http://example.com/fabrikam/acct".
Example 2-1. Example endpoint reference.
<wsa:EndpointReference xmlns:wsa="http://www.w3.org/@@@@/@@/addressing">
<wsa:Address>http://example.com/fabrikam/acct</wsa:Address>
</wsa:EndpointReference>
This specification provides no concept of endpoint identity and therefore does not provide any mechanism to determine equality or inequality of EPRs and does not specify the consequences of their equality or inequality. However, note that it is possible for other specifications to provide a comparison function that is applicable within a limited scope.
This specification does not define a lifecycle model for endpoint references and does not address the question of time-to-live for endpoint references. Other specifications that build on or use WS-Addressing may define a lifecycle model for endpoint references created according to that specification.
As noted in 2.1 Endpoint Reference Representation endpoint references are extensible. When extension attributes or elements appear as part of an endpoint reference, the processing model for such extensions is defined by the specification for those extensions. Software that processes endpoint references can safely ignore any such extensions that it does not recognise or understand.
Extensions MAY modify the rules for binding an endpoint reference to message addressing properties, or otherwise indicate that a different binding be used.
Note that this extensibility and binding behavior, when coupled with the fact that software can ignore unknown or unrecognised extensions, may result in a difference in behaviour depending on whether such an extended endpoint reference is processed by software that understands the extension(s). When designing endpoint reference extensions designers should consider whether they desire standard processing per this specification in cases where their extension is not recogonised or understood.
This section defines the information model and syntax of message addressing properties.
Note:
The Working Group requests feedback regarding the mechanism for and description of Message Addressing Property extensibility beyond the MEPs currently described in the WSDL specifications, along with use cases that illustrate how referencing specifications and other users of Addressing intend to extend them. Although the Working Group has resolved upon a particular design, some participants believe it is not adequately specified. Such feedback will help the Working Group determine whether it needs to re-examine this issue.
Message addressing properties provide references for the endpoints involved in an interaction. The use of these properties to support specific interactions is in general defined by both the semantics of the properties themselves and the implicit or explicit contract that governs the message exchange. If explicitly available, this contract can take different forms including but not being limited to WSDL MEPs and interfaces; business processes and e-commerce specifications, among others, can also be used to define explicit contracts between the parties.
The basic interaction pattern from which all others are composed is "one way". In this pattern a source sends a message to a destination without any further definition of the interaction. "Request-response" is a common interaction pattern that consists of an initial message sent by a source endpoint (the request) and a subsequent message sent from the destination of the request back to the source (the response). A response in this case can be either an application message, a fault, or any other message. Note, however, that reply messages may be sent as part of other message exchanges as well, and are not restricted to the usual single Request, single Response pattern, or to a particular WSDL MEP. The contract between the interacting parties may specify that multiple or even a variable number of replies be delivered.
The set of message addressing properties defined in this specification is sufficient for many simple variations of one-way and request-response MEPs. More advanced MEPs may require additional message addressing properties to augment the facilities provided here.
Message addressing properties collectively augment a message with the following properties (represented as XML Infosets) to support one-way, request-response, and other interaction patterns:
<wsa:To>xs:anyURI</wsa:To> ?
<wsa:From>wsa:EndpointReferenceType</wsa:From> ?
<wsa:ReplyTo>wsa:EndpointReferenceType</wsa:ReplyTo> ?
<wsa:FaultTo>wsa:EndpointReferenceType</wsa:FaultTo> ?
<wsa:Action>xs:anyURI</wsa:Action>
<wsa:MessageID>xs:anyURI</wsa:MessageID> ?
<wsa:RelatesTo RelationshipType="xs:anyURI"?>xs:anyURI</wsa:RelatesTo> *
<wsa:ReferenceParameters>xs:any*</wsa:ReferenceParameters>
The following describes the attributes and elements listed in the schema overview above:
An absolute IRI representing the address of the intended receiver of this message.
This OPTIONAL element has content of type xs:anyURI). Omitting this element is defined as being semantically equivalent to including this element with the value of "http://www.w3.org/@@@@/@@/addressing/anonymous".
This OPTIONAL element (of type wsa:EndpointReferenceType) provides the reference to the endpoint from which the message originated.
This OPTIONAL element (of type wsa:EndpointReferenceType) provides the value of the endpoint reference for the intended receiver for replies to this message.
This OPTIONAL element (of type wsa:EndpointReferenceType) provides the value of the endpoint reference for the intended receiver for faults related to this message.
This REQUIRED element (whose content is of type xs:anyURI) is an absolute IRI that uniquely identifies the semantics implied by this message.
It is RECOMMENDED that the value be an IRI identifying an input, output, or fault message within a WSDL interface. An action may be explicitly or implicitly associated with the corresponding WSDL definition. Web Services Addressing 1.0 - WSDL Binding[WS-Addressing-WSDL] describes the mechanisms of association.
This OPTIONAL element (whose content is of type xs:anyURI) is an absolute IRI that uniquely identifies the message. When present, it is the responsibility of the sender to ensure that each message is uniquely identified. The behavior of a receiver when receiving a message that contains the same /wsa:MessageID as a previously received message is unconstrained by this specification.
This OPTIONAL (repeating) element information item indicates how this message relates to another message. The content of this element (of type xs:anyURI) is an absolute IRI and corresponds to the /wsa:MessageID of the related message. The message identifier IRI may refer to a specific message, or be the following pre-defined URI that means "unspecified message": "http://www.w3.org/@@@@/@@/addressing/unspecified"
This OPTIONAL attribute (of type xs:anyURI) conveys the relationship type as an absolute IRI.
This specification has one predefined relationship type as shown in Table 3-1.
| URI | Description |
|---|---|
| "http://www.w3.org/@@@@/@@/addressing/reply" | Indicates that this is a reply to the message identified by the [message id] IRI. |
When absent, the implied value of this attribute is "http://www.w3.org/@@@@/@@/addressing/reply".
Corresponds to the value of the /wsa:ReferenceParameters of the endpoint reference to which the message is addressed. Each element information item found in /wsa:ReferenceParameter of the endpoint reference (including all of that elements [children], [attributes] and [in-scope namespaces]) is represented as is.
Note that each of the element information items described above allows attribute wildcards for future extensibility. A message processor may safely ignore any extension attribute it does not recognize.
The /wsa:To and /was:action elements indicate the target processing location and the verb or intent of the message respectively. The values of these elements can be used to facilitate the dispatch of messages.
Due to the range of network technologies currently in wide-spread use (e.g., NAT, DHCP, firewalls), many deployments cannot assign a meaningful global IRI to a given endpoint. To allow these "anonymous" endpoints to send and receive messages, WS-Addressing defines the following pre-defined URI for use by endpoints that cannot have a stable, resolvable IRI: "http://www.w3.org/@@@@/@@/addressing/anonymous". Messages whose /wsa:ReplyTo, /wsa:From and/or /wsa:FaultTo use this address MUST rely on some out-of-band mechanism for delivering replies or faults (e.g. returning the reply on the same transport connection).
A binding of WS_Addressing message addressing properties MUST reflect the property cardinality shown above. Web Services Addressing 1.0 - SOAP Binding[WS-Addressing-SOAP] defines such a binding for the SOAP [SOAP 1.2 Part 1: Messaging Framework, SOAP 1.1] protocol.
The values of the Message Addressing Properties wsa:Action, wsa:MessageID, and wsa:RelatesTo are absolute IRIs. The purpose of these IRIs is primarily identification, rather than resource retrieval. As such, simple string comparison, as indicated in Internationalized Resource Identifiers IETF RFC 3987 section 5.3.1, is sufficient to determine equivalence of these IRIs.
Comparison of wsa:To property values is out of scope, other than using simple string comparison to detect whether the value is anonymous, that is, where wsa:To has the value "http://www.w3.org/@@@@/@@/addressing/anonymous".
This section specifies the WS-Addressing-specific rules for creating a reply or fault message related to another message.
Select the appropriate EPR:
If the reply is a normal message, select the EPR from the related message's wsa:ReplyTo message addressing property. If none is present, the processor MUST fault.
Otherwise, if the reply is a fault message and the related message's wsa:FaultTo message addressing property is not empty, select the EPR from that property. If the wsa:FaultTo property is empty, select the EPR from the related message's wsa:ReplyTo message addressing property. Otherwise, if the wsa:ReplyTo property is empty, the behavior of the recipient of the related message is unconstrained by this specification.
In either of the above cases, if the related message lacks a wsa:MessageID property, the processor MUST fault.
Populate the reply message's message addressing properties:
wsa:To: this property takes the value of the selected EPR's wsa:Address
wsa:RelatesTo: this property MUST include a pair of IRIs as follows; the relationship type is the predefined reply URI "http://www.w3.org/@@@@/@@/addressing/reply" and the related message's identifier is the wsa:MessageID property value from the message being replied to; other relationships MAY be expressed in this property
wsa:ReferenceParameters: this property takes the value of the selected EPR's wsa:ReferenceParameters
The following example illustrates a message containing message addressing properties serialized as header blocks in a SOAP 1.2 message:
Example 3-1. Example message.
<S:Envelope xmlns:S="http://www.w3.org/2003/05/soap-envelope"
xmlns:wsa="http://www.w3.org/@@@@/@@/addressing">
<S:Header>
<wsa:MessageID>http://example.com/someuniquestring</wsa:MessageID>
<wsa:ReplyTo>
<wsa:Address>http://example.com/business/client1</wsa:Address>
</wsa:ReplyTo>
<wsa:To>mailto:fabrikam@example.com</wsa:To>
<wsa:Action>http://example.com/fabrikam/mail/Delete</wsa:Action>
</S:Header>
<S:Body>
<f:Delete xmlns:f="http://example.com/fabrikam">
<maxCount>42</maxCount>
</f:Delete>
</S:Body>
</S:Envelope>
This message would have the following property values:
wsa:To: "mailto:fabrikam@example.com"
wsa:ReplyTo: The endpoint with wsa:Address "http://example.com/business/client1"
wsa:Action: "http://example.com/fabrikam/mail/Delete"
wsa:MessageID: "http://example.com/someuniquestring"
The following example illustrates a reply to the above message:
Example 3-2. Example reply message.
<S:Envelope
xmlns:S="http://www.w3.org/2003/05/soap-envelope"
xmlns:wsa="http://www.w3.org/@@@@/@@/addressing">
<S:Header>
<wsa:MessageID>http://example.com/someotheruniquestring</wsa:MessageID>
<wsa:RelatesTo>http://example.com/someuniquestring</wsa:RelatesTo>
<wsa:To>http://example.com/business/client1</wsa:To>
<wsa:Action>http://example.com/fabrikam/mail/DeleteAck</wsa:Action>
</S:Header>
<S:Body>
<f:DeleteAck xmlns:f="http://example.com/fabrikam"/>
</S:Body>
</S:Envelope>
This message would have the following property values:
wsa:To: "http://example.com/business/client1"
wsa:Action: "http://example.com/fabrikam/mail/DeleteAck"
wsa:MessageID: "http://example.com/someotheruniquestring"
wsa:RelatesTo: ("http://www.w3.org/@@@@/@@/addressing/reply", "http://example.com/someuniquestring")
Users of WS-Addressing and EPRs (i.e., entities creating and receiving Message Addressing Properties and EPRs) SHOULD only use EPRs from sources they trust. For example, such users might rely on the presence of a verifiable signature by a trusted party over the EPR, or an out-of-band means of establishing trust, to determine whether they should use a particular EPR.
EPRs and message addressing properties SHOULD be integrity-protected to prevent tampering. Such optional integrity protection might be provided by the transport, a message level signature, or use of an XML digital signature within EPRs.
To prevent information disclosure, EPR issuers SHOULD NOT put sensitive information into the wsa:Address or wsa:ReferenceParameters.
Some processors may use message identifiers (wsa:MessageID) as part of a uniqueness metric in order to detect replays of messages. Care should be taken to ensure that for purposes of replay detection, the message identifier is combined with other data, such as a timestamp, so that a legitimate retransmission of the message is not confused with a replay attack. It is also advisable to use message identifiers that are not predictable, to prevent attackers from constructing and sending an unsolicited reply to a message without having to see the actual message.
When wsa:ReplyTo and/or wsa:FaultTo do not contain the anonymous URI, the processor of such an EPR should take care to avoid a denial of service attack caused by opening an excessive number network connections, which are typically a scarce resource.
Care should be taken to avoid participating in a denial of service attack in which an attacker sends messages to many receivers and includes a wsa:ReplyTo or wsa:FaultTo for the target of the attack.
This document is the work of the W3C Web Service Addressing Working Group.
Members of the Working Group are (at the time of writing, and by alphabetical order): Abbie Barbir (Nortel Networks), Rebecca Bergersen (IONA Technologies, Inc.), Andreas Bjärlestam (ERICSSON), Ugo Corda (SeeBeyond Technology Corporation), Francisco Curbera (IBM Corporation), Glen Daniels (Sonic Software), Paul Downey (BT), Jacques Durand (Fujitsu Limited), Michael Eder (Nokia), Robert Freund (Hitachi, Ltd.), Yaron Goland (BEA Systems, Inc.), Martin Gudgin (Microsoft Corporation), Arun Gupta (Sun Microsystems, Inc.), Hugo Haas (W3C/ERCIM), Marc Hadley (Sun Microsystems, Inc.), David Hull (TIBCO Software, Inc.), Yin-Leng Husband (HP), Anish Karmarkar (Oracle Corporation), Paul Knight (Nortel Networks), Philippe Le Hégaret (W3C/MIT), Mark Little (Arjuna Technologies Ltd.), Jonathan Marsh (Microsoft Corporation), Jeff Mischkinsky (Oracle Corporation), Nilo Mitra (ERICSSON), Eisaku Nishiyama (Hitachi, Ltd.), Mark Nottingham (BEA Systems, Inc.), Ales Novy (Systinet Inc.), David Orchard (BEA Systems, Inc.), Mark Peel (Novell, Inc.), Tony Rogers (Computer Associates), Tom Rutt (Fujitsu Limited), Rich Salz (DataPower Technology, Inc.), Davanum Srinivas (Computer Associates), Jiri Tejkl (Systinet Inc.), Greg Truty (IBM Corporation), Steve Vinoski (IONA Technologies, Inc.), Pete Wenzel (SeeBeyond Technology Corporation), Steve Winkler (SAP AG), Ümit Yalçınalp (SAP AG), Prasad Yendluri (webMethods, Inc.).
Previous members of the Working Group were: Lisa Bahler (SAIC - Telcordia Technologies), Marc Goodner (SAP AG), Harris Reynolds (webMethods, Inc.).
The people who have contributed to discussions on public-ws-addressing@w3.org are also gratefully acknowledged.