Web Services Eventing (WS-Eventing)

2.1 Requirements

This specification intends to meet the following requirements:

• Define means to create and delete event subscriptions.

• Define expiration for subscriptions and allow them to be renewed.

• Define how one Web service can subscribe on behalf of another.

• Define how an event source delegates subscription management to another Web service.

• Allow subscribers to specify how notifications should be delivered.

• Leverage other Web service specifications for secure, reliable, transacted message delivery.

• Support complex eventing topologies that allow the originating event source and the final event sink to be decoupled.

• Provide extensibility for more sophisticated and/or currently unanticipated subscription scenarios.

• Support a variety of encoding formats, including (but not limited to) both SOAP 1.1 [SOAP 1.1] and SOAP 1.2 [SOAP 1.2] Envelopes.

2.2 Delivery Modes

While the general pattern of asynchronous, event-based messages is extremely common, different applications often require different notification delivery mechanisms. For instance, in some cases a simple asynchronous message is optimal, while other situations may work better if the event consumer can poll for notification in order to control the flow and timing of message arrival. Some consumers will require notifications to be wrapped in a standard "event" SOAP envelope, while others will prefer messages to be delivered unwrapped. Some consumers may require notifications to be delivered reliably, while others may be willing to accept best-effort event delivery.

In order to support this broad variety of event delivery requirements, this specification introduces an abstraction called a Delivery Mode and an abstraction called Delivery Format. These concepts are used as an extension points, so that event sources and event consumers may freely create new delivery mechanisms that are tailored to their specific requirements. This specification provides a minimal amount of support for delivery mode and format negotiation by allowing an event source to provide a list of supported delivery modes and formats in response to a subscription request specifying a delivery mode or format it does not support.

When the Delivery Format feature is engaged the formatting of the going events occurs after any filtering. This ensures that regardless of what type of formatting might occur, the same Filter dialect/expression can be used to subset the event stream.

This specification defines a single delivery mode, Push Mode, which is simple asynchronous messaging.

This specification specifies two delivery formats: wrapped and unwrapped. Use of wrapped format indicates that notification messages should be contained in a wrapper element. Use of unwrapped format indicates that notification messages are not wrapped.

2.3 Subscription Managers

In some scenarios the event source itself manages the subscriptions it has created. In other scenarios, for example a geographically distributed publish-and-subscribe system, it may be useful to delegate the management of a subscription to another Web service. To support this flexibility, the response to a subscription request to an event source will include the EPR of a service that the subscriber may interact with to manage this subscription. This EPR should be the target for future requests to renew or cancel the subscription. It may address the same Web service (Address and ReferenceParameters) as the event source itself, or it may address some other Web service to which the event source has delegated management of this subscription; however, the full subscription manager EPR (Address and Reference Parameters) must be unique for each subscription.

We use the term "subscription manager" in this specification to refer to the Web service that manages the subscription, whether it is the event source itself or some separate Web service.

2.4 Example

Example 2-1 lists a hypothetical request to create a subscription for storm warnings.

(01) <s12:Envelope
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing"
(04)     xmlns:wse="http://www.w3.org/2009/02/ws-evt"
(05)     xmlns:ew="http://www.example.com/warnings" >
(06)   <s12:Header>
(07)     <wsa:Action>
(08)       http://www.w3.org/2009/02/ws-evt/Subscribe
(09)     </wsa:Action>
(10)     <wsa:MessageID>
(11)       uuid:d7c5726b-de29-4313-b4d4-b3425b200839
(12)     </wsa:MessageID>
(13)     <wsa:ReplyTo>
(14)      <wsa:Address>http://www.example.com/MyEventSink</wsa:Address>
(15)     </wsa:ReplyTo>
(16)     <wsa:To>http://www.example.org/oceanwatch/EventSource</wsa:To>
(17)   </s12:Header>
(18)   <s12:Body>
(19)     <wse:Subscribe>
(20)       <wse:Delivery>
(21)         <wse:NotifyTo>
(22)           <wsa:Address>
(23)             http://www.example.com/MyEventSink/OnStormWarning
(24)           </wsa:Address>
(25)           <wsa:ReferenceParameters>
(26)             <ew:MySubscription>2597</ew:MySubscription>
(27)           </wsa:ReferenceParameters>
(28)         </wse:NotifyTo>
(29)       </wse:Delivery>
(30)     </wse:Subscribe>
(31)   </s12:Body>
(32)
</s12:Envelope>

Lines (07-09) in Example 2-1 indicate the message is a request to create a subscription, and Line line (16) indicates that it is sent to a hypothetical event source of ocean events.

While Lines lines (13-15) indicate where a reply should be sent, Lines lines (20-29) indicate where and how notifications should be delivered; there is no requirement that these match. The absence of a Mode attribute on Line line (20) indicates that notifications should be delivered using Push mode; that is, they should be asynchronously sent as SOAP messages to the endpoint described in lines (21-28). Note that Lines lines (25-27) illustrate a typical pattern where the event sink lists a reference parameter (Line (line 26) that identifies the subscription and will be included in each notification.

Example 2-2 lists a hypothetical response to the request in Example 2-1 .

(01) <s12:Envelope
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing"
(04)     xmlns:wse="http://www.w3.org/2009/02/ws-evt"
(05)     xmlns:ow="http://www.example.org/oceanwatch" >
(06)   <s12:Header>
(07)     <wsa:Action>
(08)       http://www.w3.org/2009/02/ws-evt/SubscribeResponse
(09)     </wsa:Action>
(10)     <wsa:RelatesTo>
(11)       uuid:d7c5726b-de29-4313-b4d4-b3425b200839
(12)     </wsa:RelatesTo>
(13)     <wsa:To>http://www.example.com/MyEventSink</wsa:To>
(14)   </s12:Header>
(15)   <s12:Body>
(16)     <wse:SubscribeResponse>
(17)       <wse:SubscriptionManager>
(18)         <wsa:Address>
(19)           http://www.example.org/oceanwatch/SubscriptionManager
(20)         </wsa:Address>
(21)         <wsa:ReferenceParameters>
(22)           <ow:MyId>
(23)             28
(24)           </ow:MyId>
(25)         </wsa:ReferenceParameters>
(26)       </wse:SubscriptionManager>
(27)       <wse:Expires>P0Y0M0DT30H0M0S</wse:Expires>
(28)     </wse:SubscribeResponse>
(29)   </s12:Body>
(30)
</s12:Envelope>

Lines (07-09) in Example 2-2 indicate this message is a response to a request to create a subscription, and Lines lines (10-12) indicate that it is a response to the request in Example 2-1 . Lines lines (17-26) provide the subscription manager EPR for this subscription, and Line line (27) indicates the subscription will expire in 30 hours unless renewed.

3.1 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 [RFC2119] .

This specification uses the following syntax to define normative outlines for messages:

• The syntax appears as an XML instance, but values in italics indicate data types instead of values.

• Characters are appended to elements and attributes to indicate cardinality:

  • "?" (0 or 1)

  • "*" (0 or more)

  • "+" (1 or more)

• The character "|" is used to indicate a choice between alternatives.

• The characters "(" and ")" are used to indicate that contained items are to be treated as a group with respect to cardinality or choice.

• The characters "[" and "]" are used to call out references and property names.

• Ellipsis (i.e. "...") indicate a point of extensibility.

• XML namespace prefixes (see Table 3-1 ) are used to indicate the namespace of the element being defined.

In addition to Message Information Header properties [WS-Addressing] , this specification uses the following properties to define messages:

[Headers]

Unordered message headers.

[Action]

The value to be used for the wsa:Action URI.

[Body]

A message body.

These properties bind to a SOAP Envelope as follows:

<s:Envelope>
  <s:Header>
    [Headers]
    <wsa:Action>[Action]</wsa:Action>
    ...
  </s:Header>
  <s:Body>[Body]</s:Body>
</s:Envelope>

3.2 Considerations on the Use of Extensibility Points

The elements defined in this specification MAY be extended at the points indicated by their outlines and schema. Implementations MAY add child elements and/or attributes at the indicated extension points but MUST NOT contradict the semantics of the parent and/or owner, respectively. If a receiver does not recognize an extension, the receiver SHOULD ignore that extension. Senders MAY indicate the presence of an extension that has to be understood through the use of a corresponding SOAP Header with a soap:mustUnderstand attribute with the value "1".

Extension elements and attributes MUST NOT use the Web Services Eventing namespace URI.

3.3 XML Namespaces

The XML namespace URI that MUST be used by implementations of this specification is:

http://www.w3.org/2009/02/ws-evt

Table 3-1 lists XML namespaces that are used in this specification. The choice of any namespace prefix is arbitrary and not semantically significant.

The working group intends to update the value of the Web Services Eventing namespace URI each time a new version of this document is published until such time that the document reaches Candidate Recommendation status. Once it has reached Candidate Recommendation status, the working group intends to maintain the value of the Web Services Eventing namespace URI that was assigned in the Candidate Recommendation unless significant changes are made that impact the implementation or break post-CR implementations of the specification. Also see http://www.w3.org/2001/tag/doc/namespaceState.html and http://www.w3.org/2005/07/13-nsuri .

3.4 Terminology

Delivery Mode

The mechanism by which notifications are delivered from the source to the sink.

Event Source

A Web service that sends notifications and accepts requests to create subscriptions.

Event Sink

A Web service that receives notifications.

Notification

A one-way message sent to indicate that an event, or events, have occurred.

Push Mode

A delivery mechanism where the source sends notifications to the sink as unsolicited, asynchronous SOAP messages.

Subscriber

A Web service that sends requests to create, renew, and/or delete subscriptions.

Subscription Manager

A Web service that accepts requests to create, manage, get the status of, renew, and/or delete subscriptions on behalf of an event source.

3.5 Compliance

An implementation is not compliant with this specification if it fails to satisfy one or more of the MUST or REQUIRED level requirements defined herein. A SOAP Node MUST NOT use the XML namespace identifier for this specification (listed in 3.3 XML Namespaces ) within SOAP Envelopes unless it is compliant with this specification.

Normative text within this specification takes precedence over the XML Schema and WSDL descriptions, which in turn take precedence over outlines, which in turn take precedence over examples.

All messages defined by this specification MUST be sent to a Web service that is addressable by an EPR (see [WS-Addressing] ).

4.1 Subscribe

To create a subscription, a subscriber sends a request message of the following form to an event source:

[Action]
  http://www.w3.org/2009/02/ws-evt/Subscribe
[Body]
  <wse:Subscribe ...>
    <wse:EndTo> endpoint-reference </wse:EndTo> ?
    <wse:Delivery Mode="xs:anyURI"? ...> xs:any* </wse:Delivery>
    <wse:Format Name="xs:anyURI"? > xs:any* </wse:Format> ?
    <wse:Expires> (xs:dateTime | xs:duration) </wse:Expires> ?
    <wse:Filter Dialect="xs:anyURI"? ...> xs:any* </wse:Filter> ?
    xs:any*
</wse:Subscribe>

The following describes additional, normative constraints on the outline listed above:

[Body] /wse:Subscribe/wse:EndTo

Where to send a SubscriptionEnd message if the subscription is terminated unexpectedly. (See 4.5 Subscription End .) If present, this element MUST be of type wsa:EndpointReferenceType. Default is not to send this message. The endpoint to which the EndTo EPR refers MUST support the SubcriptionEndPortType portType.

Note, subscribers wishing to correlate SubscriptionEnd messages with the subscription to which they apply MAY wish to add a distinguishing reference parameter to the EndTo EPR. For convenience in this common situation, this specification defines a global element, wse:Identifier of type xs:anyURI, that MAY be used as a distinguishing reference parameter.

[Body] /wse:Subscribe/wse:Delivery

A delivery destination for notification messages, using some delivery mode. See 2.2 Delivery Modes for details.

[Body] /wse:Subscribe/wse:Delivery/@Mode

The delivery mode to be used for notification messages sent in relation to this subscription. Implied value is "http://www.w3.org/2009/02/ws-evt/DeliveryModes/Push", which indicates that Push Mode delivery should be used. See 2.2 Delivery Modes for details.

If the event source does not support the requested delivery mode, the request MUST fail, and the event source MAY MUST generate a wse:DeliveryModeRequestedUnavailable fault indicating that the requested delivery mode is not supported.

[Body] /wse:Subscribe/wse:Delivery/@Mode="http://www.w3.org/2009/02/ws-evt/DeliveryModes/Push"

Value of [Body] /wse:Subscribe/wse:Delivery MUST contain at least the single element, wse:NotifyTo, that contains the endpoint reference to which notification messages should be sent. The value of this element is not constrained for other delivery modes.

[Body] /wse:Subscribe/wse:Format

This optional element contains the delivery format to be used for notification messages sent in relation to this subscription. Implied value is "http://www.w3.org/2009/02/ws-evt/DeliveryFormats/Unwrap", which indicates that unwraped delivery should be used. See Section 2.2 Delivery Modes for details.

If the event source does not support the requested delivery format, the request MUST generate a wse:DeliveryFormatRequestedUnavailable fault indicating that the requested delivery format is not supported.

[Body] /wse:Subscribe/wse:Format@Name="http://www.w3.org/2009/02/ws-evt/DeliveryFormats/Unwrap"

Indicate the unwrapped event delivery format.

[Body] /wse:Subscribe/wse:Format@Name="http://www.w3.org/2009/02/ws-evt/DeliveryFormats/Wrap"

Indicate the wrapped event delivery format.

[Body] /wse:Subscribe/wse:Expires

Requested expiration time for the subscription. (No implied value.) The event source defines the actual expiration and is not constrained to use a time less or greater than the requested expiration. The expiration time may be a specific time or a duration from the subscription's creation time. Both specific times and durations are interpreted based on the event source's clock.

If this element does not appear, then the request is for a subscription that will not expire. That is, the subscriber is requesting the event source to create a subscription with an indefinite lifetime. If the event source grants such a subscription, it may be terminated by the subscriber using an Unsubscribe request, or it may be terminated by the event source at any time for reasons such as connection termination, resource constraints, or system shut-down.

If the expiration time is either a zero duration or a specific time that occurs in the past according to the event source, then the request MUST fail, and the event source MAY MUST generate a wse:InvalidExpirationTime fault indicating that an invalid expiration time was requested.

Some event sources may not have a "wall time" clock available, and so are only able to accept durations as expirations. If such a source receives a Subscribe request containing a specific time expiration, then the request MAY fail; if so, the event source MAY MUST generate a wse:UnsupportedExpirationType fault indicating that an unsupported expiration type was requested.

[Body] /wse:Subscribe/wse:Filter

A Boolean expression in some dialect, either as a string or as an XML fragment (see [ [Body]/wse:Subscribe/wse:Filter/@Dialect ] ). If the expression evaluates to false for a notification, the notification MUST NOT be sent to the event sink. Implied value is an expression that always returns true. If the event source does not support filtering, then a request that specifies a filter MUST fail, and the event source MAY MUST generate a wse:FilteringNotSupported fault indicating that filtering is not supported.

If the event source supports filtering but cannot honor the requested filtering, the request MUST fail, and the event source MAY MUST generate a wse:FilteringRequestedUnavailable fault indicating that the requested filter dialect is not supported.

It is possible for a Subscribe request to contain a filter that will never evaluate to true for the lifetime of the Subscription. If an Event Source detects this condition it MAY MUST generate a wse:EmptyFilter fault in response to the Subscribe request message.

[Body] /wse:Subscribe/wse:Filter/@Dialect

Implied value is "http://www.w3.org/TR/1999/REC-xpath-19991116".

While an XPath predicate expression provides great flexibility and power, alternate filter dialects may be defined. For instance, a simpler, less powerful dialect might be defined for resource-constrained implementations, or a new dialect might be defined to support filtering based on data not included in the notification message itself. If desired, a filter dialect could allow the definition of a composite filter that contained multiple filters from other dialects.

[Body] /wse:Subscribe/wse:Filter/@Dialect=" http://www.w3.org/TR/1999/REC-xpath-19991116 "

Value of [Body] /wse:Subscribe/wse:Filter is an XPath [XPath 1.0] predicate expression (PredicateExpr); the context of the expression is:

• Context Node: the SOAP Envelope containing root of the notification. event XML.

• Context Position: 1.

• Context Size: 1.

• Variable Bindings: None.

• Function Libraries: Core Function Library [XPath 1.0] .

• Namespace Declarations: The [in-scope namespaces] property [XML Infoset] of /s:Envelope/s:Body/*/wse:Filter.

Other message information headers defined by WS-Addressing [WS-Addressing] MAY be included in the request and response messages, according to the usage and semantics defined in WS-Addressing.

Other components of the outline above are not further constrained by this specification.

If included within the Subscribe request message, the wse:NotifyTo and wse:EndTo SHOULD have some cursory validity checking performed before the Subscribe response is returned. While not all errors can be detected prior to sending a message to those EPRs, some obvious ones can be detected. For example, an unsupported transport specified within the wsa:Address IRI. Detecting these errors during Subscribe processing will lessen the chances of the subscriber creating an unusable subscription. If this check is performed and a problem is detected then the event source MAY MUST generate a wse:UnusableEPR fault rather than returning the SubscribeResponse message.

If the event source accepts a request to create a subscription, it MUST reply with a response of the following form:

[Action]
  http://www.w3.org/2009/02/ws-evt/SubscribeResponse
[Body]
  <wse:SubscribeResponse ...>
    <wse:SubscriptionManager>
      wsa:EndpointReferenceType
    </wse:SubscriptionManager>
    <wse:Expires>(xs:dateTime | xs:duration)</wse:Expires>
    xs:any*
</wse:SubscribeResponse>

The following describes additional, normative constraints on the outline listed above:

[Body] /wse:SubscribeResponse/wse:SubscriptionManager

The EPR of the subscription manager for this subscription.

In some cases, it is convenient for all EPRs issued by a single event source to address a single Web service and use a reference parameter to distinguish among the active subscriptions. For convenience in this common situation, this specification defines a global element, wse:Identifier of type xs:anyURI, that MAY be used as a distinguishing reference parameter if desired by the event source.

[Body] /wse:SubscribeResponse/wse:Expires

The expiration time assigned by the event source. The expiration time MAY be either an absolute time or a duration but SHOULD be of the same type as the requested expiration (if any).

If this element does not appear, then the subscription will not expire. That is, the subscription has an indefinite lifetime. It may be terminated by the subscriber using an Unsubscribe request, or it may be terminated by the event source at any time for reasons such as connection termination, resource constraints, or system shut-down.

Other components of the outline above are not further constrained by this specification.

If the event source chooses not to accept a subscription, the request MUST fail, and the event source MAY MUST generate a wse:EventSourceUnableToProcess fault indicating that the request was not accepted.

Example 4-1 lists another hypothetical request to create a subscription.

(01) <s12:Envelope 
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing"
(04)     xmlns:wse="http://www.w3.org/2009/02/ws-evt"
(05)     xmlns:ew="http://www.example.com/warnings" >
(06)   <s12:Header>
(07)     <wsa:Action>
(08)       http://www.w3.org/2009/02/ws-evt/Subscribe
(09)     </wsa:Action>
(10)     <wsa:MessageID>
(11)       uuid:e1886c5c-5e86-48d1-8c77-fc1c28d47180
(12)     </wsa:MessageID>
(13)     <wsa:ReplyTo>
(14)      <wsa:Address>http://www.example.com/MyEvEntsink</wsa:Address>
(15)      <wsa:ReferenceParameters>
(16)        <ew:MySubscription>2597</ew:MySubscription>
(17)      </wsa:ReferenceParameters>
(18)     </wsa:ReplyTo>
(19)     <wsa:To>http://www.example.org/oceanwatch/EventSource</wsa:To>
(20)   </s12:Header>
(21)   <s12:Body>
(22)     <wse:Subscribe>
(23)       <wse:EndTo>
(24)         <wsa:Address>
(25)           http://www.example.com/MyEventSink
(26)         </wsa:Address>
(27)         <wsa:ReferenceParameters>
(28)           <ew:MySubscription>2597</ew:MySubscription>
(29)         </wsa:ReferenceParameters>
(30)       </wse:EndTo>
(31)       <wse:Delivery>
(32)         <wse:NotifyTo>
(33)           <wsa:Address>
(34)             http://www.other.example.com/OnStormWarning
(35)           </wsa:Address>
(36)           <wsa:ReferenceParameters>
(37)             <ew:MySubscription>2597</ew:MySubscription>
(38)           </wsa:ReferenceParameters>
(39)         </wse:NotifyTo>
(40)       </wse:Delivery>
(41)       <wse:Expires>2004-06-26T21:07:00.000-08:00</wse:Expires>
(42)       <wse:Filter xmlns:ow="http://www.example.org/oceanwatch"
(43)           Dialect="http://www.example.org/topicFilter" >
(44)         weather.storms
(45)       </wse:Filter>
(46)     </wse:Subscribe>
(47)   </s12:Body>
(48)

(42)       <wse:Filter xmlns:ow="http://www.example.org/oceanwatch" >
(43)         /*/ow:Speed/[node() &gt; 50]
(44)       </wse:Filter>
(45)     </wse:Subscribe>
(46)   </s12:Body>
(47)

</s12:Envelope>

Like the request in Example 2-1 , Lines lines (07-09) of Example 4-1 indicate the message is a request to create a subscription. Line (19) indicates that it is sent to a hypothetical event source of ocean events.

Lines (13-18) indicate where to send the response to this request, Lines lines (23-30) indicate where to send a SubscriptionEnd message if necessary, and Lines lines (31-34) indicate how and where to send notifications.

Line (41) indicates the event sink would prefer to have the subscription expire on 26 June 2004 at 9:07 PM Pacific time.

Lines (42-45) (42-44) indicate the event sink only wants weather reports where topic the speed of wind is storms, using a custom filter dialect. greater than 50.

Example 4-2 lists a hypothetical response to the request in Example 4-1 .

(01) <s12:Envelope 
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing"
(04)     xmlns:wse="http://www.w3.org/2009/02/ws-evt"
(05)     xmlns:ew="http://www.example.com/warnings"
(06)     xmlns:ow="http://www.example.org/oceanwatch" >
(07)   <s12:Header>
(08)     <wsa:Action>
(09)       http://www.w3.org/2009/02/ws-evt/SubscribeResponse
(10)     </wsa:Action>
(11)     <wsa:RelatesTo>
(12)       uuid:e1886c5c-5e86-48d1-8c77-fc1c28d47180
(13)     </wsa:RelatesTo>
(14)     <wsa:To>http://www.example.com/MyEventSink</wsa:To>
(15)     <ew:MySubscription wsa:IsReferenceParameter="true">
(16)       2597
(17)     </ew:MySubscription>
(18)   </s12:Header>
(19)   <s12:Body>
(20)     <wse:SubscribeResponse>
(21)       <wse:SubscriptionManager>
(22)         <wsa:Address>
(23)           http://www.example.org/oceanwatch/SubscriptionManager
(24)         </wsa:Address>
(25)         <wsa:ReferenceParameters>
(26)           <wse:Identifier>

(26)           <x:SubID xmlns:x="http://example.com">

(27)             uuid:22e8a584-0d18-4228-b2a8-3716fa2097fa
(28)           </wse:Identifier>

(28)           </x:SubID>

(29)         </wsa:ReferenceParameters>
(30)       </wse:SubscriptionManager>
(31)       <wse:Expires>2004-07-01T00:00:00.000-00:00</wse:Expires>
(32)     </wse:SubscribeResponse>
(33)   </s12:Body>
(34)
</s12:Envelope>

Like the response in Example 2-2 , Lines lines (08-10) of Example 4-2 indicate this message is a response to a request to create a subscription, and Lines lines (11-13) indicate that it is a response to the request in Example 4-1 . Lines (14-17) indicate the response is sent to the event sink indicated in Lines lines (13-18) of Example 4-1 . Lines (21-30) provide the address of the subscription manager for this subscription; note that this particular response uses the global wse:Identifier x:SubID element defined by as a reference parameter to distinguish this specification. subscription EPR from other subscription EPRs. Finally, Line line (31) indicates the subscription will expire on 1 July 2004 unless renewed; there is no requirement that this time be necessarily longer or shorter than the requested expiration (Line (line (41) of Example 4-1 ).

4.2 Renew

To update the expiration for a subscription, subscription managers MUST support requests to renew subscriptions.

To renew a subscription, the subscriber sends a request of the following form to the subscription manager:

[Action]
  http://www.w3.org/2009/02/ws-evt/Renew
[Body]
  <wse:Renew ...>
    <wse:Expires>(xs:dateTime | xs:duration)</wse:Expires> ?
    xs:any*
</wse:Renew>

Components of the outline listed above are additionally constrained as for a request to create a subscription (see 4.1 Subscribe ). Other components of the outline above are not further constrained by this specification.

If the subscription manager accepts a request to renew a subscription, it MUST reply with a response of the following form:

[Action]
  http://www.w3.org/2009/02/ws-evt/RenewResponse
[Body]
  <wse:RenewResponse ...>
    <wse:Expires>(xs:dateTime | xs:duration)</wse:Expires> ?
    xs:any*
</wse:RenewResponse>

Components of the outline listed above are constrained as for a response to a subscribe request (see 4.1 Subscribe ) with the following addition(s):

[Body] /wse:RenewResponse/wse:Expires

If the requested expiration is a duration, then the implied start of that duration is the time when the subscription manager starts processing the Renew request.

If the subscription manager chooses not to renew this subscription, the request MUST fail, and the subscription manager MAY MUST generate a wse:UnableToRenew fault indicating that the renewal was not accepted.

Other components of the outline above are not further constrained by this specification.

Example 4-3 lists a hypothetical request to renew the subscription created in Example 4-2 .

(01) <s12:Envelope 
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing"
(04)     xmlns:wse="http://www.w3.org/2009/02/ws-evt"
(05)     xmlns:ow="http://www.example.org/oceanwatch" >
(06)   <s12:Header>
(07)     <wsa:Action>
(08)       http://www.w3.org/2009/02/ws-evt/Renew
(09)     </wsa:Action>
(10)     <wsa:MessageID>
(11)       uuid:bd88b3df-5db4-4392-9621-aee9160721f6
(12)     </wsa:MessageID>
(13)     <wsa:ReplyTo>
(14)      <wsa:Address>http://www.example.com/MyEventSink</wsa:Address>
(15)     </wsa:ReplyTo>
(16)     <wsa:To>
(17)       http://www.example.org/oceanwatch/SubscriptionManager
(18)     </wsa:To>
(19)     <wse:Identifier wsa:IsReferenceParameter="true">

(19)     <x:SubID wsa:IsReferenceParameter="true" xmlns:x="http://example.com">

(20)       uuid:22e8a584-0d18-4228-b2a8-3716fa2097fa
(21)     </wse:Identifier>

(21)     </x:SubID>

(22)   </s12:Header>
(23)   <s12:Body>
(24)     <wse:Renew>
(25)       <wse:Expires>2004-06-26T21:07:00.000-08:00</wse:Expires>
(26)     </wse:Renew>
(27)   </s12:Body>
(28)
</s12:Envelope>

Lines (07-09) indicate this is a request to renew a subscription. Lines (19-21) contain the reference parameter that indicates the subscription to be renewed is the one created in Example 4-2 . Line (25) in Example 4-3 indicates the request is to extend the subscription until 26 June 2004 at 9:07 PM Pacific.

Example 4-4 lists a hypothetical response to the request in Example 4-3 .

(01) <s12:Envelope
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing"
(04)     xmlns:wse="http://www.w3.org/2009/02/ws-evt"
(05)     xmlns:ow="http://www.example.org/oceanwatch" >
(06)   <s12:Header>
(07)     <wsa:Action>
(08)      http://www.w3.org/2009/02/ws-evt/RenewResponse
(09)     </wsa:Action>
(10)     <wsa:RelatesTo>
(11)       uuid:bd88b3df-5db4-4392-9621-aee9160721f6
(12)     </wsa:RelatesTo>
(13)     <wsa:To>http://www.example.com/MyEventSink</wsa:To>
(14)   </s12:Header>
(15)   <s12:Body>
(16)     <wse:RenewResponse>
(17)       <wse:Expires>2004-06-26T12:00:00.000-00:00</wse:Expires>
(18)     </wse:RenewResponse>
(19)   </s12:Body>
(20)
</s12:Envelope>

Line (17) in Example 4-4 indicates the subscription has been extended only until 26 June 2004 at noon.

4.3 GetStatus

To get the status of a subscription, the subscriber sends a request of the following form to the subscription manager:

[Action]
  http://www.w3.org/2009/02/ws-evt/GetStatus
[Body]
  <wse:GetStatus ...>
    xs:any*
</wse:GetStatus>

Components of the outline listed above are additionally constrained as for a request to renew a subscription (see 4.2 Renew ). Other components of the outline above are not further constrained by this specification.

If the subscription is valid and has not expired, the subscription manager MUST reply with a response of the following form:

[Action]
  http://www.w3.org/2009/02/ws-evt/GetStatusResponse
[Body]
  <wse:GetStatusResponse ...>
    <wse:Expires>(xs:dateTime | xs:duration)</wse:Expires> ?
    xs:any*
</wse:GetStatusResponse>

Components of the outline listed above are constrained as for a response to a renew request (see 4.2 Renew ). Other components of the outline above are not further constrained by this specification.

Example 4-5 lists a hypothetical request to get the status of the subscription created in Example 4-2 .

(01) <s12:Envelope
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing"
(04)     xmlns:wse="http://www.w3.org/2009/02/ws-evt"
(05)     xmlns:ow="http://www.example.org/oceanwatch" >
(06)   <s12:Header>
(07)     <wsa:Action>
(08)       http://www.w3.org/2009/02/ws-evt/GetStatus
(09)     </wsa:Action>
(10)     <wsa:MessageID>
(11)       uuid:bd88b3df-5db4-4392-9621-aee9160721f6
(12)     </wsa:MessageID>
(13)     <wsa:ReplyTo>
(14)       <wsa:Address>http://www.example.com/MyEventSink</wsa:Address>
(15)     </wsa:ReplyTo>
(16)     <wsa:To>
(17)       http://www.example.org/oceanwatch/SubscriptionManager
(18)     </wsa:To>
(19)     <wse:Identifier wsa:IsReferenceParameter="true">

(19)     <x:SubID wsa:IsReferenceParameter="true" xmlns:x="http://example.com">

(20)       uuid:22e8a584-0d18-4228-b2a8-3716fa2097fa
(21)     </wse:Identifier>

(21)     </x:SubID>

(22)   </s12:Header>
(23)   <s12:Body>
(24)     <wse:GetStatus />
(25)   </s12:Body>
(26)
</s12:Envelope>

Lines (07-09) indicate this is a request to get the status of a subscription. Lines (16-21) indicate that the request is sent to the subscription manager for the subscription created in Example 4-2 .

Example 4-6 lists a hypothetical response to the request in Example 4-5 .

(01) <s12:Envelope 
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing"
(04)     xmlns:wse="http://www.w3.org/2009/02/ws-evt"
(05)     xmlns:ow="http://www.example.org/oceanwatch" >
(06)   <s12:Header>
(07)     <wsa:Action>
(08)       http://www.w3.org/2009/02/ws-evt/GetStatusResponse
(09)     </wsa:Action>
(10)     <wsa:RelatesTo>
(11)       uuid:bd88b3df-5db4-4392-9621-aee9160721f6
(12)     </wsa:RelatesTo>
(13)     <wsa:To>http://www.example.com/MyEventSink</wsa:To>
(14)   </s12:Header>
(15)   <s12:Body>
(16)     <wse:GetStatusResponse>
(17)       <wse:Expires>2004-06-26T12:00:00.000-00:00</wse:Expires>
(18)     </wse:GetStatusResponse>
(19)   </s12:Body>
(20)
</s12:Envelope>

Line (17) in Example 4-6 indicates the subscription will expire on 26 June 2004 at noon.

4.4 Unsubscribe

Though subscriptions expire eventually, to minimize resources, the subscribing event sink SHOULD explicitly delete a subscription when it no longer wants notifications associated with the subscription.

To explicitly delete a subscription, a subscribing event sink sends a request of the following form to the subscription manager:

[Action]
  http://www.w3.org/2009/02/ws-evt/Unsubscribe
[Body]
  <wse:Unsubscribe ...>
    xs:any*
</wse:Unsubscribe>

Components of the outline above are additionally constrained only as for a request to renew a subscription (see 4.2 Renew ). For example, the faults listed there are also defined for a request to delete a subscription.

If the subscription manager accepts a request to delete a subscription, it MUST reply with a response of the following form:

[Action]
  http://www.w3.org/2009/02/ws-evt/UnsubscribeResponse
[Body]
  <wse:UnsubscribeResponse ...>
    xs:any*
</wse:UnsubscribeResponse>

Components of the outline listed above are not further constrained by this specification.

Example 4-7 lists a hypothetical request to delete the subscription created in Example 4-2 .

(01) <s12:Envelope 
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing"
(04)     xmlns:wse="http://www.w3.org/2009/02/ws-evt"
(05)     xmlns:ow="http://www.example.org/oceanwatch" >
(06)   <s12:Header>
(07)     <wsa:Action>
(08)       http://www.w3.org/2009/02/ws-evt/Unsubscribe
(09)     </wsa:Action>
(10)     <wsa:MessageID>
(11)       uuid:2653f89f-25bc-4c2a-a7c4-620504f6b216
(12)     </wsa:MessageID>
(13)     <wsa:ReplyTo>
(14)      <wsa:Address>http://www.example.com/MyEventSink</wsa:Address>
(15)     </wsa:ReplyTo>
(16)     <wsa:To>
(17)       http://www.example.org/oceanwatch/SubscriptionManager
(18)     </wsa:To>
(19)     <wse:Identifier wsa:IsReferenceParameter="true">

(19)     <x:SubID wsa:IsReferenceParameter="true" xmlns:x="http://example.com">

(20)       uuid:22e8a584-0d18-4228-b2a8-3716fa2097fa
(21)     </wse:Identifier>

(21)     </x:SubID>

(22)   </s12:Header>
(23)   <s12:Body>
(24)     <wse:Unsubscribe />
(25)   </s12:Body>
(26)
</s12:Envelope>

Lines (07-09) in Example 4-7 indicate the message is a request to delete a subscription. Lines (16-21) indicate that the request is addressed to the manager for the subscription created in Example 4-2 .

Example 4-8 lists a hypothetical response to the request in Example 4-7 .

(01) <s12:Envelope 
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing" >
(04)   <s12:Header>
(05)     <wsa:Action>
(06)       http://www.w3.org/2009/02/ws-evt/UnsubscribeResponse
(07)     </wsa:Action>
(08)     <wsa:RelatesTo>
(09)       uuid:2653f89f-25bc-4c2a-a7c4-620504f6b216
(10)     </wsa:RelatesTo>
(11)     <wsa:To>http://www.example.com/MyEventSink</wsa:To>
(12)   </s12:Header>
(13)   <s12:Body>
(14)     <wse:UnsubscribeResponse/>
(15)   </s12:Body>
(16)
</s12:Envelope>

4.5 Subscription End

If the event source terminates a subscription unexpectedly, the event source SHOULD send a Subscription End SOAP message to the endpoint reference indicated when the subscription was created (see 4.1 Subscribe ). This endpoint reference MUST refer to an endpoint that supports the SubscriptionEndPortType portType. The message MUST be of the following form:

[Action]
  http://www.w3.org/2009/02/ws-evt/SubscriptionEnd
[Body]
  <wse:SubscriptionEnd ...>
    <wse:Status>
      ( http://www.w3.org/2009/02/ws-evt/DeliveryFailure | 
        http://www.w3.org/2009/02/ws-evt/SourceShuttingDown |
        http://www.w3.org/2009/02/ws-evt/SourceCancelling )
    </wse:Status>
    <wse:Reason xml:lang="language identifier" >xs:string</wse:Reason> ?
    xs:any*
</wse:SubscriptionEnd>

The following describes additional, normative constraints on the outline listed above:

[Body] /wse:SubscriptionEnd/wse:Status = "http://www.w3.org/2009/02/ws-evt/DeliveryFailure"

This value MUST be used if the event source terminated the subscription because of problems delivering notifications.

[Body] /wse:SubscriptionEnd/wse:Status = "http://www.w3.org/2009/02/ws-evt/SourceShuttingDown"

This value MUST be used if the event source terminated the subscription because the source is being shut down in a controlled manner; that is, if the event source is being shut down but has the opportunity to send a SubscriptionEnd message before it exits.

[Body] /wse:SubscriptionEnd/wse:Status = "http://www.w3.org/2009/02/ws-evt/SourceCancelling"

This value MUST be used if the event source terminated the subscription for some other reason before it expired.

[Body] /wse:SubscriptionEnd/wse:Reason

This optional element contains text, in the language specified by the @xml:lang attribute, describing the reason for the unexpected subscription termination.

Other message information headers defined by WS-Addressing [WS-Addressing] MAY be included in the message, according to the usage and semantics defined in WS-Addressing.

Other components of the outline above are not further constrained by this specification.

Example 4-9 lists a hypothetical SubscriptionEnd message corresponding to an early termination of the subscription created in Example 4-1 .

(01) <s12:Envelope 
(02)     xmlns:s12="http://www.w3.org/2003/05/soap-envelope"
(03)     xmlns:wsa="http://www.w3.org/2005/08/addressing"
(04)     xmlns:wse="http://www.w3.org/2009/02/ws-evt" 
(05)     xmlns:ew="http://www.example.com/warnings" >
(06)   <s12:Header>
(07)     <wsa:Action>
(08)       http://www.w3.org/2009/02/ws-evt/SubscriptionEnd
(09)     </wsa:Action>
(10)     <wsa:To>http://www.example.com/MyEventSink</wsa:To>
(11)     <ew:MySubscription wsa:IsReferenceParameter="true">
(12)       2597
(13)     </ew:MySubscription>
(14)   </s12:Header>
(15)   <s12:Body>
(16)     <wse:SubscriptionEnd>
(17)       <wse:Status>wse:SourceShuttingDown</wse:Status>
(18)       <wse:Reason xml:lang="en-US" >
(19)         Event source going off line.
(20)       </wse:Reason>
(21)     </wse:SubscriptionEnd>
(22)   </s12:Body>
(23)
</s12:Envelope>

Line (08) is the action URI for Subscription End. Lines (10-13) indicate the message is sent to the EndTo of the subscribe request (Lines (lines (23-30) in Example 4-1 .). Line (17) indicates the event source is shutting down, and Lines lines (18-20) indicate that the event source was going off line.

6.1 Fault Detail RetryAfter Element

The following element is used to convey additional information in the faults.

/wse:RetryAfter

This element (whose content is of type xs:unsignedLong) is a suggested minimum duration in milliseconds to wait before retransmitting the message. Omission of this element indicates that a retry is never likely to succeed.

/wse:RetryAfter/@any

Optional extensibility attributes that do not affect processing.

6.2 DeliveryModeRequestedUnavailable

This fault is sent when a Subscribe request specifies a delivery mode that is not supported by the event source. Optionally, this fault may contain a list of supported delivery mode URIs in the Detail property.

6.3 InvalidExpirationTime

This fault is sent when a Subscribe request specifies an expiration time that is in the past or an expiration duration of zero.

6.4 UnsupportedExpirationType

This fault is sent when a Subscribe request specifies an expiration time and the event source is only capable of accepting expiration durations; for instance, if the event source does not have access to absolute time.

6.5 FilteringNotSupported

This fault is sent when a Subscribe request contains a filter and the event source does not support filtering.

6.6 FilteringRequestedUnavailable

This fault is sent when a Subscribe request specifies a filter dialect that the event source does not support. Optionally, this fault may contain a list of supported filter dialect URIs in the Detail property.

6.7 EventSourceUnableToProcess

This fault is sent when the event source is not capable of fulfilling a Subscribe request for local reasons unrelated to the specific request.

6.8 UnableToRenew

This fault is sent when the event source is not capable of fulfilling a Renew request for local reasons unrelated to the specific request.

6.9 InvalidMessage

If a request message does not comply with the corresponding outline listed above, the request MUST fail and the event source or subscription manager MAY MUST generate the following fault indicating that the request is invalid:

6.10 DeliveryFormatRequestUnavailable

This fault is sent when a Subscribe request specifies a delivery mode format that is not supported by the event source. Optionally, this fault may contain a list of supported delivery mode format URIs in the Detail property.

6.11 EmptyFilter

This fault MAY be generated when an Event Source detects a wse:Subscribe request containing a filter that, for whatever reason, will never evaluate to true.

6.12 UnusableEPR

This fault MAY be generated when an Event Source detects that the wse:NotifyTo or wse:EndTo EPR is unusable.

7.1 Message Security

It is strongly RECOMMENDED that the communication between services be secured using the mechanisms described in WS-Security [WS-Security] . In order to properly secure messages, the body and all relevant headers need to be included in the signature. Specifically, any headers identified in the <wse:NotifyTo> element and standard messaging headers, such as those from WS-Addressing [WS-Addressing] , need to be signed with the body in order to "bind" the two together. For messages with empty bodies, the <s12:Body> element should be signed so content cannot be added in transit.

Different security mechanisms may be desired depending on the frequency of messages. For example, for infrequent messages, public key technologies may be adequate for integrity and confidentiality. However, for high-frequency events, it may be more performant to establish a security context for the events using the mechanisms described in WS-Trust [WS-Trust] and WS-SecureConversation [WS-SecureConversation] .

It should be noted that if a shared secret is used it is RECOMMENDED that derived keys be used to strengthen the secret as described in WS-SecureConversation.

The following list summarizes common classes of attacks that apply to this protocol and identifies the mechanism to prevent/mitigate the attacks:

• Message alteration - Alteration is prevented by including signatures of the message information using WS-Security.

• Message disclosure - Confidentiality is preserved by encrypting sensitive data using WS-Security.

• Key integrity - Key integrity is maintained by using the strongest algorithms possible (by comparing secured policies - see WS-Policy [WS-Policy] and WS-SecurityPolicy [WS-SecurityPolicy] ).

• Authentication - Authentication is established using the mechanisms described in WS-Security and WS-Trust. Each message is authenticated using the mechanisms described in WS-Security.

• Accountability - Accountability is a function of the type of and string of the key and algorithms being used. In many cases, a strong symmetric key provides sufficient accountability. However, in some environments, strong PKI signatures are required.

• Availability - All reliable messaging services are subject to a variety of availability attacks. Replay detection is a common attack and it is RECOMMENDED that this be addressed by the mechanisms described in WS-Security. Other attacks, such as network-level denial of service attacks are harder to avoid and are outside the scope of this specification. That said, care should be taken to ensure that minimal state is saved prior to any authenticating sequences.

• Replay - Messages may be replayed for a variety of reasons. To detect and eliminate this attack, mechanisms should be used to identify replayed messages such as the timestamp/nonce outlined in WS-Security. Alternatively, and optionally, other technologies, such as sequencing, can also be used to prevent replay of application messages.

7.2 Access Control

It is important for event sources to properly authorize requests. This is especially true for Subscribe requests, as otherwise the ability to subscribe on behalf of a third-party event sink could be used to create a distributed denial-of-service attack.

Some possible schemes for validating Subscribe requests include:

• Send a message to the event sink that describes the requested subscription, and then wait for a confirmation message to be returned by the event sink, before the event source accepts the subscription request. While this provides strong assurance that the event sink actually desires the requested subscription, it does not work for event sinks that are not capable of sending a confirmation, and requires additional logic on the event sink.

• Require user authentication on the Subscribe request, and allow only authorized users to Subscribe.

Other mechanisms are also possible. Note that event sources that are not reachable from the Internet have less need to control Subscribe requests.