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Re: Coordinated Choreographies Proposal 6 - Extending Choreographies

From: Monica J. Martin <Monica.Martin@Sun.COM>
Date: Tue, 09 Nov 2004 16:20:02 -0800
To: Haugen Robert <Robert.Haugen@choreology.com>
Cc: public-ws-chor@w3.org
Message-id: <41915EB2.40608@sun.com>


Bob,
In thinking about nested choreographies, you could have a child derived 
from a parent OR a child that is dependent on a parent but not extended 
from it.
Can we address either case (Proposal 6 includes the former only).

Thanks.

>Haugen: Coordinated Choreographies WS-CDL Spec Changes
>Plain text inline, pdf to come Monday, word.doc sent on request.
>
>Extending Choreographies
>
>The extends mechanism provides a kind of inheritance relationship from
>parent CDL elements to child CDL elements.
>
>The result is a merger of the behaviors of both parent and child
>packages and/or choreographies.
>
>The benefits of this mechanism include:
>*	providing standard interaction patterns to be emulated by child
>choreographies, as in industry business protocol standards;
>*	providing patterns for coordination/transaction protocols;
>*	providing a mechanism for tool support for choreography
>patterns.
>
>The extends mechanism only allows single inheritance, that is, a child
>choreography can extend one and only one parent choreography.  However,
>one parent choreograph may be extended by many child choreographies.
>
>Any CDL element with a name may be extended by a compatible child
>element.  That includes: a Package as a whole, Role Types, Participant
>Types, Channel Types, Relationship Types, Information Types, a
>Choreography as a whole, Variables, Tokens, Work Units, Interactions,
>Exchanges, Records, Exception Blocks and Finalizer Blocks.
>
>With one exception, the syntax is very simple: the second statement of
>the child element which is to extend a parent element must take the
>form:
>   <extends name=ncname/>
>where ncname is the name of the parent element to be extended, which
>must be of the same type as the child element.
>
>The exception is Packages, where the syntax is:
>   <extends name=<uri>/>
>
>[Part of this proposal is to add an optional extends element to each of
>the CDL elements listed above. Alternatively, extends could be an
>attribute. ]
>
>Extends for inner elements of a choreography can only be used inside a
>choreography which is itself extended.
>
>This mechanism imposes some constraints on parent elements: 
>*	A parent element to be extended must have a name.
>*	If a parent choreography performs another choreography, the
>performed choreography must be enclosed within the parent choreography.
>The parent choreography cannot perform another choreography that is
>outside its scope.
>o	However, a choreography designer would be well advised to keep
>parent choreographies simple.  Performing even enclosed choreographies
>makes the parent-child relationship much more complex.
>
>Notably excluded from being extended are Ordering Structures, which do
>not have names.  The Ordering Structures of the parent choreography must
>be reproduced exactly in the child choreography.
>
>Other than for elements of Ordering Structures, "merger of behaviors"
>means that any elements of the parent choreography that are not extended
>by the child, still occur in the merged choreography. For these
>unextended elements to work properly in the merged choreography, the
>child choreography may need to extend (alias) the roles and variables
>involved. It also means that the child choreography has no mechanism to
>turn off or override parent behaviors.  [Should we add one?]
>
>"Merger of behaviors" also means that the child may add additional
>behaviors that are not present in the parent, and they will also occur
>in the merged choreography.  
>
>Extending an element usually amounts to mapping names of child elements
>to parent elements, e.g. mapping role and variables names from something
>abstract (for example, a protocol role like "Superior") to something
>concrete (for example, a business role like "CreditRequestor"). 
>
>In all cases, extending an element does not change any of its attributes
>except for those whose values have already been extended by the same
>child.   For example, in an Interaction, channels, relationships, roles,
>etc. might be overridden by child-extended versions of the elements
>specified in the parent. 
>
>It is invalid for the child to override with a value that was not
>extended from the element specified in the parent element.  For example,
>if the parent element specified a roleType, the extended child element
>must specify a roleType that was extended from the same roleType as in
>the parent element.  It is also invalid for the child to change a simple
>value that cannot be extended, e.g. causeException="true". 
>
>However, the child may add more Work Units to extended Choreographies
>and more activities to Work Units, and may add additional respond
>Exchanges and Records with causeException="true" to Interactions.  
>
>In every case where a child adds elements that are not extended from
>parent elements, the child elements are added in at the end of the
>parent elements in the directly enclosing extended CDL construct, and
>are to be executed in sequence after the parent elements.  For example,
>if the child adds activities to an extended Work Unit, the additional
>activities are added after the last parent activity in the extended Work
>Unit.
>
>In the case of coordination protocols, it may not be necessary to define
>every aspect of the protocol in the parent choreography.  For example,
>the parent choreography below can be bound to a variety of business
>transaction protocols, but the underlying protocols have more signals
>than are shown in the choreography.  It may only be useful to put
>interactions that might have business content into the choreography,
>while the lower-level protocol signals are handled by transaction
>infrastructure software.
>
>Moreover, while bindings to coordination and other underlying protocols
>are not specified by WS-CDL, we assume that they will be required in
>many situations (see the explanation of the Choreography coordination
>attribute in Section ? and the discussion about Coordination/Transaction
>Protocols in Section 6).  In such situations, the protocol needs only to
>be bound once for the parent choreography, to be inherited by the
>children.
> 
>Example
>
>This example shows a coordinated parent Choreography modelling a generic
>business transaction protocol, extended by a Credit Authorization
>Choreography that follows the protocol.
>
>[The example uses Nick's exception-throwing proposal. The
>exception-throwing mechanism does not affect the Extends proposal.]
>
>   <roleType name="Superior">
>      <behavior name="superiorForInferior"/>
>   </roleType>
>   <roleType name="Inferior">
>      <behavior name="inferiorForSuperior"/>
>   </roleType>
>   <relationshipType name="SuperiorInferior">
>      <role type="tns:Superior" behavior="superiorForInferior"/>
>      <role type="tns:Inferior" behavior="inferiorForSuperior"/>
>   </relationshipType>
>   <informationType name="refusalType" exceptionType="true"/>
>   
>   <!-- Extensions -->
>   <roleType name="CreditRequestor">
>      <extends name="Superior"/>
>      <behavior name="requestCredit">
>         <extends name="superiorForInferior"/>
>      </behavior>
>   </roleType>
>   <roleType name="CreditResponder">
>      <extends name="Inferior"/>
>      <behavior name="extendCredit">
>         <extends name="inferiorForSuperior"/>
>      </behavior>
>   </roleType>
>   <relationshipType name="CreditReqCreditResp">
>      <extends name="SuperiorInferior"/>
>   </relationshipType>   
>   <informationType name="creditDeniedType">
>      <extends name="refusalType"/>
>   </informationType>
>   
>   <!-- Parent Coordination choreography with new exceptions-->
>   <choreography name="Coordination" root="false" coordinated="true">
>      <relationship type="tns:SuperiorInferior"/>
>      <variableDefinition>
>         <variable name="state" silentAction="true"/>
>         <variable name="requestAndContext"/>
>         <variable name="positiveResponse"/>
>         <variable name="refusal" informationType="tns:refusalType"/>
>      </variableDefinition>
>      
>      <!-- the normal work - receive the request and decide whether to
>approve -->
>      <interaction name="activePhase" channelVariable="tns:coordination"
>operation="propagate">
>         <participate relationship="SuperiorInferior"
>fromRole="tns:Superior" toRole="Inferior"/>
>         <exchange name="propagate" informationType="requestAndContext"
>action="request">
>            <send variable="tns:requestAndContext"/>
>            <receive variable="tns:requestAndContext"/>
>         </exchange>
>         <exchange name="prepared" informationType="positiveResponse"
>action="respond">
>            <send variable="tns:positiveResponse"/>
>            <receive variable="tns:positiveResponse"/>
>         </exchange>
>         <exchange name="refused" informationType="refusal"
>action="respond">
>            <send variable="tns:refusal" causeException="true"/>
>            <receive variable="tns:refusal" causeException="true"/>
>         </exchange>
>      </interaction>
>      
>      <!-- catch the exception - as an exception it will abort the
>choreography and the finalizers are not accessible -->
>      <exception name="handleRefusedException">
>         <interaction name="refused" channelVariable="tns:coordination"
>operation="refused">
>            <participate relationship="SuperiorInferior"
>fromRole="tns:Inferior" toRole="Superior"/>
>         </interaction>
>      </exception>
>      
>      <!-- Finalizers -->
>      <!-- what to do if the decision is to confirm -->
>      <finalizer name="confirm">
>         <interaction name="confirm" channelVariable="tns:coordination"
>operation="confirm">
>            <participate relationship="SuperiorInferior"
>fromRole="tns:Superior" toRole="Inferior"/>
>         </interaction>
>      </finalizer>
>      <!-- what to do if the decision is to cancel -->
>      <finalizer name="cancel" default="true">
>         <interaction name="cancel" channelVariable="tns:coordination"
>operation="cancel">
>            <participate relationship="SuperiorInferior"
>fromRole="tns:Superior" toRole="Inferior"/>
>         </interaction>
>      </finalizer>
>   </choreography>
>   
>   <!-- Coordination child CreditAuthorization  choreography -->
>   <choreography name="CreditAuthorization" root="false"
>coordinated="true">
>      <extends name="Coordination"/>
>      <relationship type="tns:CreditReqCreditResp"/>
>      <variableDefinition>
>         <variable name="CreditExtended" informationType="xsd:int"
>silentAction="true" roleType="tns:CreditResponder"/>
>         <variable name="creditRequest">
>            <extends name="requestAndContext"/>
>         </variable>
>         <variable name="creditAuthorized">
>            <extends name="positiveResponse"/>
>         </variable>
>         <variable name="creditDenied">
>            <extends name="refusal"/>
>         </variable>
>      </variableDefinition>
>      
>      <!-- the normal work - receive the request and decide whether to
>approve -->
>      <interaction name="creditAuthorization"
>channelVariable="tns:CreditRequestor">
>         <extends name="activePhase"/>
>         <participate relationship="SuperiorInferior"
>fromRole="tns:Superior" toRole="Inferior"/>
>         <exchange name="creditRequest"
>informationType="creditRequestType" action="request">
>            <extends name="propagate"/>
>            <send variable="tns:creditRequest"/>
>            <receive variable="tns:creditRequest"/>
>         </exchange>
>         <exchange name="creditAuthorized"
>informationType="creditAuthorizedType" action="respond">
>            <extends name="prepared"/>
>            <send variable="tns:creditAuthorized"/>
>            <receive variable="tns:creditAuthorized"/>
>         </exchange>
>         <exchange name="creditDenied"
>informationType="creditDeniedType" action="respond">
>            <extends name="refused"/>
>            <send variable="tns:creditDenied" causeException="true"/>
>            <receive variable="tns:creditDenied" causeException="true"/>
>         </exchange>
>      </interaction>
>      
>      <!-- catch the (application) exception - as an exception it will
>abort the choreography and the finalizers are not accessible -->
>      <exception name="handleBadCreditException">
>         <extends name="handleRefusedException"/>
>         <interaction channelVariable="tns:CreditResponder"
>operation="creditDenied">
>            <extends name="refused"/>
>            <participate relationship="CreditReqCreditResp"
>fromRole="tns:Responder" toRole="CreditRequestor"/>
>         </interaction>
>      </exception>
>      
>      <!-- Finalizers -->
>      <!-- what to do if the credit is drawn down -->
>      <finalizer name="drawDown">
>         <extends name="confirm"/>
>         <!-- if there is no application content to send, this could
>just be an assignment to the statecapturevariable creditExtended -->
>         <interaction channelVariable="tns:CreditRequestor"
>operation="drawDown">
>            <extends name="confirm"/>
>            <participate relationship="CreditReqCreditResp"
>fromRole="tns:CreditRequestor" toRole="CreditResponder"/>
>            <record when="before">
>               <source value="drawnDown"/>
>               <target variable="CreditExtended"/>
>            </record>
>         </interaction>
>      </finalizer>
>      <!-- what to do if the credit is not used -->
>      <finalizer name="replenish" case="cancel" default="true">
>         <extends name="cancel"/>
>         <!-- if there is no application content to send, this could
>just be an assignment to the statecapturevariable creditExtended -->
>         <interaction channelVariable="tns:CreditRequestor"
>operation="replenish">
>            <extends name="cancel"/>
>            <participate relationship="CreditReqCreditResp"
>fromRole="tns:CreditRequestor" toRole="CreditResponder"/>
>            <record when="before">
>               <source value="released"/>
>               <target variable="CreditExtended"/>
>            </record>
>         </interaction>
>      </finalizer>
>   </choreography>
>
>
>Choreology Anti virus scan completed
>  
>
Received on Wednesday, 10 November 2004 00:20:03 GMT

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