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RE: Issue 996 - A proposal

From: Tony Fletcher <tony_fletcher@btopenworld.com>
Date: Sat, 26 Feb 2005 16:01:21 -0000
To: "'Gary Brown'" <gary@enigmatec.net>, <public-ws-chor@w3.org>
Message-ID: <000001c51c1c$6b300ba0$6401a8c0@corp.choreology.com>
Dear Gary,
 
I have been thinking about your proposal and I think it works all right.
One concern is that it looks fine as you have written it but what if other
stuff starts being inserted between the different parts of the one
'operation'?  Putting within an interaction bracket makes it clear (and the
spec can and should state this) that all the enclosed exchanges are part of
the same semantically coupled set of messages and the only things that can
be interspersed between them are endpoint 'events', such as the current
'record' that are directly coupled to that message exchange.  So long as we
keep the coupling then I am not too worried about the precise syntax.  (Or
to put it another way I want to prevent people from being 'silly' and just
scattering parts of the same 'myop' liberally around the description, just
because the spec does not say you can not do that!)
 
I am concerned that we somehow have the ability to say that a request
message may have more than one valid response message associated with it.
 
Best Regards     Tony
A M Fletcher
 
Cohesions  (TM)
 
Business transaction management software for application coordination
www.choreology.com <http://www.choreology.com/> 
 
Choreology Ltd., 68 Lombard Street, London EC3V 9LJ     UK
Tel: +44 (0) 1473 729537   Mobile: +44 (0) 7801 948219
tony.fletcher@choreology.com     (Home: amfletcher@iee.org)
-----Original Message-----
From: public-ws-chor-request@w3.org [mailto:public-ws-chor-request@w3.org]
On Behalf Of Gary Brown
Sent: 25 February 2005 09:00
To: Tony Fletcher; public-ws-chor@w3.org
Subject: Re: Issue 996 - A proposal


Hi Tony
 
Just to clarify, in my example below I was referring to an MEP where the two
responses were received in sequence, so in this case there is no choice
necessary - i.e. one response is not being favoured over another.
 
However, if we wanted to model the two mutually exclusive response case,
then it could be modelled as:
 
<interaction op="myop" >
    <exchange action="request" />
</interaction>
<choice>
    <interaction op="myop" >
        <exchange action="response" name="firstResponse" />
    <interaction>
    <interaction op="myop" >
        <exchange action="response" name="secondResponse" />
    </interaction>
</choice>
 
This is similar to your solution but just externalises the choice outside
the interaction. The only addition required here is to provide a name with
the exchange response - which would map to the messageLabel in the WSDL
(which answers your other question).
 
Regards
Gary

----- Original Message ----- 
From: Tony Fletcher <mailto:tony_fletcher@btopenworld.com>  
To: 'Gary Brown' <mailto:gary@enigmatec.net>  ; public-ws-chor@w3.org 
Sent: Thursday, February 24, 2005 9:55 PM
Subject: RE: Issue 996 - A proposal


Dear Gary,
 
Thank you for a thoughtful response - as always from you.  I have embedded a
few responses below.
 


Best Regards     Tony
A M Fletcher
 
Cohesions  (TM)
 
Business transaction management software for application coordination
www.choreology.com
 
Choreology Ltd., 68 Lombard Street, London EC3V 9LJ     UK
Tel: +44 (0) 1473 729537   Mobile: +44 (0) 7801 948219
tony.fletcher@choreology.com     (Home: amfletcher@iee.org)

-----Original Message-----
From: Gary Brown [mailto:gary@enigmatec.net] 
Sent: 24 February 2005 19:30
To: Tony Fletcher; public-ws-chor@w3.org
Subject: Re: Issue 996 - A proposal


Hi Tony
 
If this proposal is accepted, then I think it would need to reference the
response's 'messageLabel' (as mentioned in Arthur's email) in the exchange
element. 
<Tony>Very likely.  I agree we would need to study WSDL 2.0 in sufficient
detail to determine what we would need to make a clear linkage, although if
the responses have unique names I am not sure what they would add. </Tony> 
 
However, what is to prevent a MEP having multiple request messages? Is this
covered in WSDL2? 
<Tony>Do not know.  Again we would need to study WSDL 2.0.  I said one
request as I assumed that it was the request name that distinguished one
'operation' or set of request and allowable responses from another.  Do you
have a particular 'use case' in mind, where you would need to do as a single
unit rather than having the ability to send requests 'in parallel' (where
each request had its own define pattern of allowed responses)?  Even if the
multiple request case is theoretically possible I would have thought it is a
bit of an 'edge' case and we could omit for an 80 - 90% case solution.
</Tony>  
 
Although we do have a charter to bind to WSDL2, I am not sure that CDL
necessarily needs to be so literal in the way that it expresses the
interactions that will map to a particular MEP. We do need to ensure that
CDL could describe the message exchanges that may be defined within a WSDL
definition, but I don't think this needs to necessarily be confined to a
single interaction. 
<Tony> I agree in principle - see above as well</Tony>
 
For example - if you have a MEP that has one request followed by two
responses, then one approach would be to model it with two interactions, the
first having the req-resp exchange elements and the second interaction
having the second response exchange. 
 <Tony> But in this case it seems to me that you are 'favouring' one
response over another.  If both are legitimate responses of equal standing,
why should there be a need to treat them differently in the choreo
description?</Tony>
 
At model verification time, the overall sequence of message exchanges for
the interactions in CDL could be compared against those in the WSDL
definition - and if the second response is not found to follow the initial
req-resp in all cases, then this would generate an error.
<Tony> Yes certainly should be able to check that the sequencing of messages
according to the choreo description is supported by the WS description. (It
may not be the only one supported in general.)</Tony>
 
Regards
Gary

----- Original Message ----- 
From: Tony Fletcher <mailto:tony_fletcher@btopenworld.com>  
To: public-ws-chor@w3.org 
Sent: Thursday, February 24, 2005 4:28 PM
Subject: Issue 996 - A proposal

Dear Colleagues,
 
I am informed by the Web Service Description group that WSDL 2.0 in its
current draft form is able to describe the possibility of having several
response messages for a (single) request message (refer to
http://lists.w3.org/Archives/Public/public-ws-chor/2005Feb/0024.html).
 
As a resolution for Issue 996 I therefore propose that the following changes
are made to the CDL specification:
 
1)  It is made clear that an 'interaction' element can only have one
'exchange' element with action="request".
 
2)  That an 'interaction' element can have more than one 'exchange' element
with action="response".
   a) the responses occur in the lexical order the are written in (i.e. with
no wrapping element they occur in the sequence they are written)
   b) if the responses, or a subset of them, are contained within a 'choice'
element then one but only one of the responses in the choice occur
   c) if the responses, or a subset of them, are contained within a 'set'
element then they all may occur and in any order
 
3)  The text with regard to causeException as left as is, that is there can
be zero, one, or more exception causing (or fault) messages listed as
responses in an interaction and they form an implicit 'choice' group (that
is only one of them can occur).
 
4) If there are multiple responses defined then a CDL endpoint may emit an
exception causing message after emitting one or more normal responses
according to the definition.  It is invalid to emit a normal response after
emitting an exception causing message.  A receiver may choose to receive a
normal response message after receiving an exception causing message (within
a single interaction definition) as it may have been generated before the
exception causing message or may ignore it and just act on the exception
causing message.
 
5) Amend the CDL schema as follows:
 
 <complexType name="tInteraction">
    <complexContent>
      <extension base="cdl:tExtensibleElements">
        <sequence>
          <element name="participate" type="cdl:tParticipate"/>
          <element name="exchangeGroup" type="cdl:tExchangeGroup"
minOccurs="0"  maxOccurs="unbounded"/>
          <element name="timeout" type="cdl:tTimeout" minOccurs="0"
maxOccurs="1"/>
          <element name="record" type="cdl:tRecord" minOccurs="0"
maxOccurs="unbounded"/>
        </sequence>
        <attribute name="name" type="NCName" use="required"/>
        <attribute name="channelVariable" type="QName" use="required"/>
        <attribute name="operation" type="NCName" use="required"/>
        <attribute name="align" type="boolean" use="optional"
default="false"/>
        <attribute name="initiate" type="boolean"  use="optional"
default="false"/>
      </extension>
    </complexContent>
  </complexType>
 
 <complexType name="tExchangeGroup">
    <complexContent>
      <extension base="cdl:tExtensibleElements">
        <choice>
            <element name="exchange" type="cdl:tExchange"/>
            <element name="choice" type="cdl:tChoiceExchange"/>
            <element name="set" type="cdl:tSetExchange"/>
          </choice>
       </extension>
    </complexContent>
  </complexType>
 

<complexType name="tChoiceExchange">
    <complexContent>
      <extension base="cdl:tExtensibleElements">
        <sequence>
            <element name="exchange" type="cdl:tExchange"/>
        </sequence>
      </extension>
    </complexContent>
  </complexType>
 
<complexType name="tSetExchange">
    <complexContent>
      <extension base="cdl:tExtensibleElements">
        <sequence>
            <element name="exchange" type="cdl:tExchange"/>
        </sequence>
      </extension>
    </complexContent>
  </complexType>
 

Examples:
So the following would all become valid.
 
A)
<interaction name="ABCF" channelVariable="tns:aChannel" operation="a"> 
      <participate relationshipType="SuperiorInferior"
fromRole="tns:Superior" toRole="Inferior"/> 
      <exchange name="A" informationType="Atype" action="request">
              <send variable="tns:A"/>
              <receive variable="tns:A"/>
       </exchange>
       <exchange name="B" informationType="BType" action="respond">
              <send variable="tns:B"/>
              <receive variable="tns:B"/>
        </exchange>
        <exchange name="C" informationType="CType" action="respond">
              <send variable="tns:C"/> 
              <receive variable="tns:C"/>
        </exchange>
        <exchange name="F" informationType="FType" action="respond">
              <send variable="tns:F" causeException="true"/>
              <receive variable="tns:F" causeException="true"/>
        </exchange>
</interaction>
 
B)

<interaction name="ABCF" channelVariable="tns:aChannel" operation="a"> 
      <participate relationshipType="SuperiorInferior"
fromRole="tns:Superior" toRole="Inferior"/> 
      <exchange name="A" informationType="Atype" action="request">
              <send variable="tns:A"/>
              <receive variable="tns:A"/>
       </exchange>
    <choice>
        <exchange name="B" informationType="BType" action="respond">
              <send variable="tns:B"/>
              <receive variable="tns:B"/>
        </exchange>
        <exchange name="C" informationType="CType" action="respond">
              <send variable="tns:C"/> 
              <receive variable="tns:C"/>
        </exchange>
     </choice>
        <exchange name="D" informationType="DType" action="respond">
              <send variable="tns:D"/> 
              <receive variable="tns:D"/>
        </exchange>
        <exchange name="F" informationType="FType" action="respond">
              <send variable="tns:F" causeException="true"/>
              <receive variable="tns:F" causeException="true"/>
        </exchange>
</interaction>
 
C)
<interaction name="ABCF" channelVariable="tns:aChannel" operation="a"> 
      <participate relationshipType="SuperiorInferior"
fromRole="tns:Superior" toRole="Inferior"/> 
      <exchange name="A" informationType="Atype" action="request">
              <send variable="tns:A"/>
              <receive variable="tns:A"/>
       </exchange>
    <set> 
        <exchange name="B" informationType="BType" action="respond">
              <send variable="tns:B"/>
              <receive variable="tns:B"/>
        </exchange>
        <exchange name="C" informationType="CType" action="respond">
              <send variable="tns:C"/> 
              <receive variable="tns:C"/>
        </exchange>
     </set>
        <exchange name="D" informationType="DType" action="respond">
              <send variable="tns:D"/> 
              <receive variable="tns:D"/>
        </exchange>
        <exchange name="F" informationType="FType" action="respond">
              <send variable="tns:F" causeException="true"/>
              <receive variable="tns:F" causeException="true"/>
        </exchange>
</interaction>
 
Note:  I added the 'set' element as seemed to be a logical extension of the
ideas.  If other are uncomfortable with it then I would be happy to see it
removed.  I think the sequence and choice possibilities for multiple
responses will cover at least  80% of the cases.
 


Best Regards     Tony
A M Fletcher
 
Cohesions  (TM)
 
Business transaction management software for application coordination
www.choreology.com <http://www.choreology.com/> 
 
Choreology Ltd., 68 Lombard Street, London EC3V 9LJ     UK
Tel: +44 (0) 1473 729537   Mobile: +44 (0) 7801 948219
tony.fletcher@choreology.com     (Home: amfletcher@iee.org)

 
Received on Saturday, 26 February 2005 16:01:54 GMT

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