%entities; ]>
&wsa-core.title; &w3c-designation-wsa-core; &document.status; &draft.day; &draft.month; &draft.year; &w3c-designation-wsa-core; &altlocs; &prevloc; &wsa-core.latest; Martin Gudgin Microsoft Corp Marc Hadley Sun Microsystems, Inc

Web Services Addressing provides transport-neutral mechanisms to address Web services and messages. &wsa-core.title; (this document) defines a set of abstract properties and an XML Infoset [] representation thereof 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.

 &status; English

Last Modified: $Date: 2005/07/12 18:46:50 $
Introduction

&wsa-core.title; (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 &wsa-soap.title;[] for more information on the use of WS-Addressing in SOAP):

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="&nsuri;"> (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.

 Notational Conventions

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 [].

When describing abstract data models, this specification uses the notational convention used by the XML Infoset []. Specifically, abstract property names always appear in square brackets (e.g., [some property]).

When describing concrete XML information items, this specification uses the notational convention of 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/> in XML Schema 1.0 for XML 1.0 serialization). The use of @{any} indicates the presence of an attribute wildcard (<xs:anyAttribute/> in XML Schema 1.0 for XML 1.0 serialization). 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.

When defining the cardinality of endpoint reference properties and message addressing properties, this specification uses the following notation: (n..m), where n is the minimum allowed number of ocurrances of the property and m is the maximum allowed number of occurances. When n has the same value as m then exactly that number of ocurrances of the property must be present in the associated endpoint reference or message.

 Namespaces

This specification uses a number of namespace prefixes throughout; they are listed in . Note that the choice of any namespace prefix is arbitrary and not semantically significant (see []).

Prefixes and Namespaces used in this specification
Prefix Namespace
S http://www.w3.org/2003/05/soap-envelope
wsa &nsuri;
xs http://www.w3.org/2001/XMLSchema

WS-Addressing may be used with SOAP [, ] as described in &wsa-soap.title;[]. WS-Addressing may be used with WSDL [, ] described services as described in &wsa-wsdl.title;[]. Examples in this specification use an XML 1.0 [] representation but this is not a requirement.

All information items defined by this specification are identified by the XML namespace URI [] &nsuri;. A normative XML Schema [, ] document for XML 1.0 serialization can be obtained by dereferencing the XML namespace URI.

 Endpoint References

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.

 Information Model for Endpoint References

An endpoint reference consists of the following abstract properties:

An absolute IRI representing the address of the endpoint. This specification introduces two predefined [address] values as shown in .

Predefined [address] values
URI Description
&nsuri;/anonymous 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. This URI is used to allow such endpoints to send and receive messages. Messages sent to EPRs whose [address] is this value MUST rely on some out-of-band mechanism for delivery (e.g. using a pre-existing transport connection) from a prior interaction.
&nsuri;/none Messages sent to EPRs whose [address] is this value MUST be discarded (i.e. not sent). This URI is typically used in EPRs that designate a reply or fault endpoint (see section ) to indicate that no reply or fault message should be sent.

A reference may contain a number of individual parameters that 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 - &wsa-soap.title;[] describes the default binding for the SOAP protocol.

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 ) or retrieval of metadata from an authoritative source, SHOULD be used.

 Endpoint Reference XML Infoset Representation

This section defines an XML Infoset-based representation for an endpoint reference as both an XML element (<wsa:EndpointReference>) and as an XML type (wsa:EndpointReferenceType) for XML 1.0 serialization which MAY be used wherever a Web service endpoint is referenced in an XML 1.0 document. 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.

<wsa:EndpointReference> <wsa:Address>IRI</wsa:Address> <wsa:ReferenceParameters>{any}*</wsa:ReferenceParameters> ? <wsa:Metadata>{any}*</wsa:Metadata>? </wsa:EndpointReference>

The following describes the attributes and elements listed in the schema overview above:

This represents an Endpoint Reference. This example uses the predefined <wsa:EndpointReference> element, but any element of the same type (of the wsa:EndpointReferenceType for an XML 1.0 serialization) may be used.

This REQUIRED element, whose content is an IRI (of type xs:anyURI for an XML 1.0 serialization), specifies the [address] property of the endpoint reference.

This is an extensibility mechanism to allow additional attributes to be specified.

This OPTIONAL element may contain elements from any namespace. Such elements form the [reference parameters] of the reference.

This is an extensibility mechanism to allow additional attributes to be specified.

Each element information item found in [reference parameters] (including all of that elements [children], [attributes] and [in-scope namespaces]) is represented as is.

This OPTIONAL element may contain elements from any namespace. Such elements form the metadata that is relevant to the interaction with the endpoint.

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[] 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 endpoint reference. <wsa:EndpointReference xmlns:wsa="&nsuri;"> <wsa:Address>http://example.com/fabrikam/acct</wsa:Address> </wsa:EndpointReference> Endpoint Reference Comparison

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.

 Endpoint Reference Lifecycle

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.

 Endpoint Reference Extensibility

As noted in 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.

Extension elements and attributes MAY add additional properties to an endpoint reference in addition to those specified in . Endpoint reference extensions MAY modify the value of one or more existing properties of an endpoint reference. Extensions MAY modify the rules for binding endpoint reference properties to message addressing properties, or otherwise indicate that a different binding be used.

Note that this ability to modify existing properties 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 recognized or understood.

 Message Addressing Properties

This section defines the information model and syntax of message addressing properties.

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 transmission primitive or 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.

Abstract Property Definitions

Message addressing properties collectively augment a message with the following abstract properties to support one-way, request-response, and other interaction patterns:

An absolute IRI representing the address of the intended receiver of this message.

Reference to the endpoint from which the message originated.

An endpoint reference for the intended receiver for replies to this message.

An endpoint reference for the intended receiver for faults related to this message.

An absolute IRI that uniquely identifies the semantics implied by this message.

It is RECOMMENDED that the value of the [action] property is an IRI identifying an input, output, or fault message within a WSDL interface or port type. An action may be explicitly or implicitly associated with the corresponding WSDL definition. &wsa-wsdl.title;[] describes the mechanisms of association.

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 [message id] as a previously received message is unconstrained by this specification.

A pair of values that indicate how this message relates to another message. The type of the relationship is identified by an absolute IRI. The related message is identified by an absolute IRI that corresponds to the related message's [message id] property. The message identifier IRI may refer to a specific message, or be the following pre-defined URI that means "unspecified message": &nsuri;/unspecified

This specification has one predefined relationship type as shown in .

Predefined [relationship] values
URI Description
&nsuri;/reply Indicates that this is a reply to the message identified by the [message id] IRI.

Corresponds to the value of the [reference parameters] property of the endpoint reference to which the message is addressed.

The [destination] and [action] properties indicate the target processing location and the verb or intent of the message respectively. The values of these properties can be used to facilitate the dispatch of messages.

A binding of WS_Addressing message addressing properties MUST reflect the property cardinality shown above. &wsa-soap.title;[] defines such a binding for the SOAP [, ] protocol.

 XML Infoset Representation of Message Addressing Properties

The following shows the XML Infoset representation of the message addressing properties defined in :

<wsa:To>IRI</wsa:To> <wsa:From>Endpoint Reference</wsa:From> <wsa:ReplyTo>Endpoint Reference</wsa:ReplyTo> <wsa:FaultTo>Endpoint Reference</wsa:FaultTo> <wsa:Action>IRI</wsa:Action> <wsa:MessageID>IRI</wsa:MessageID> <wsa:RelatesTo RelationshipType="IRI"?>IRI</wsa:RelatesTo> <wsa:ReferenceParameters>{any}*</wsa:ReferenceParameters>

The following describes the attributes and elements listed in the schema overview above:

This OPTIONAL element, whose content is an IRI (of type xs:anyURI for an XML 1.0 serialization), provides the value for the [destination] property. If this element is NOT present then the value of the [destination] property is &nsuri;/anonymous.

This OPTIONAL element, an Endpoint Reference as defined in (of type wsa:EndpointReferenceType for an XML 1.0 serialization), provides the value for the [source endpoint] property.

This OPTIONAL element, an Endpoint Reference as defined in (of type wsa:EndpointReferenceType for an XML 1.0 serialization), provides the value for the [reply endpoint] property. If this element is NOT present then the value of the [address] property of the [reply endpoint] EPR is &nsuri;/anonymous.

This OPTIONAL element, an Endpoint Reference as defined in (of type wsa:EndpointReferenceType for an XML 1.0 serialization), provides the value for the [fault endpoint] property.

This REQUIRED element, whose content is an IRI (of type xs:anyURI for an XML 1.0 serialization), conveys the value of the [action] property.

This OPTIONAL element, whose content is an IRI (of type xs:anyURI for an XML 1.0 serialization), conveys the [message id] property.

This OPTIONAL (repeating) element information item contributes one abstract [relationship] property value, in the form of an (IRI, IRI) pair. The content of this element (of type xs:anyURI for an XML 1.0 serialization) conveys the [message id] of the related message.

This OPTIONAL attribute, whose content is an IRI (of type xs:anyURI for an XML 1.0 serialization), conveys the relationship type. When absent, the implied value of this attribute is &nsuri;/reply.

Each element information item found in [reference parameters] (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.

Comparing IRIs

The values of the Message Addressing Properties [action], [message id], and [relationship] 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 section 5.3.1, is sufficient to determine equivalence of these IRIs.

Comparison of [destination] property values is out of scope, other than using simple string comparison to detect whether the value is anonymous, that is, where [destination] has the value "&nsuri;/anonymous".

 Formulating a Reply Message

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 [reply endpoint] message addressing property. If none is present, the processor MUST fault.

When using the XML Infoset representation, in the absence of a wsa:ReplyTo element the value of the [reply endpoint] message addressing property defaults to an EPR with an [address] property of &nsuri;/anonymous - see section .

Otherwise, if the reply is a fault message and the related message's [fault endpoint] message addressing property is not empty, select the EPR from that property. If the [fault endpoint] property is empty, select the EPR from the related message's [reply endpoint] message addressing property. Otherwise, if the [reply endpoint] 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 [message id] property, the processor MUST fault.

If the selected EPR's [address] property is &nsuri;/none the reply message is discarded, if not then populate the reply message's message addressing properties:

[destination]: this property takes the value of the selected EPR's [address] property.

[relationship]: this property MUST include a pair of IRIs as follows; the relationship type is the predefined reply URI &nsuri;/reply and the related message's identifier is the [message id] property value from the message being replied to; other relationships MAY be expressed in this property

[reference parameters]: this property takes the value of the selected EPR's [reference parameters] property

The following example illustrates a message containing message addressing properties serialized as header blocks in a SOAP 1.2 message:

Example message. <S:Envelope xmlns:S="http://www.w3.org/2003/05/soap-envelope" xmlns:wsa="&nsuri;"> <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:

[destination]: mailto:fabrikam@example.com

[reply endpoint]: The endpoint with [address] http://example.com/business/client1

[action]: http://example.com/fabrikam/mail/Delete

[message id]: http://example.com/someuniquestring

The following example illustrates a reply to the above message:

Example reply message. <S:Envelope xmlns:S="http://www.w3.org/2003/05/soap-envelope" xmlns:wsa="&nsuri;"> <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:

[destination]: http://example.com/business/client1

[action]: http://example.com/fabrikam/mail/DeleteAck

[message id]: http://example.com/someotheruniquestring

[relationship]: (&nsuri;/reply, http://example.com/someuniquestring)

 Security Considerations

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 [address] or [reference parameters] properties.

Some processors may use message identifiers ([message id]) as part of a uniqueness metric in order to detect replays of messages. In this case, 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 [reply endpoint] and/or [fault endpoint] 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 [reply endpoint] or [fault endpoint] for the target of the attack.

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