RE: Issue 998 - State that sequential lexically ordering is the default for interpretation of CDL

Dear Gary and others,
 
Having had a careful look at the specification including the schema I now
see that you are quite correct - I wish someone had pointed that out on the
call!!
 
More than that the schema is carefully crafted such that you can only ever
have one activity in series except within an explicit SEQUENCE, PARALLEL or
CHOICE construct.  So my second solution has already been adopted!  So we
could leave as is, which I suspect is what folk will be inclined to to do,
or we could do what I was originally suggesting, which would be to relax
this rule, allow a series of activities to legally occur and make the
semantics implicitly 'sequence' by adding the default rule.
 
I have to say that this was not immediately obvious.  It is from the schema,
and can be inferred from the informal schema fragments found in the body of
the specification.  
 
Suggested changes to clarify the situation for others:
In Section 2.4.5 Choreographies 8th paragraph change from: A Choreography
MUST contain an <emph>Activity-Notation</emph>. The Activity-Notation
specifies the actions of the Choreography that perform the actual work.  
 
to: A Choreography MUST contain a single <emph>Activity-Notation</emph>. The
Activity-Notation MAY contain within it other Activity-Notations and it
specifies the actions of the Choreography that perform the actual work. 
 
So that has dealt with activities, and I think the situation with the
elements "below" activities is clear so that brings us back to
choreographies which is the subject of your other email on relationships
which I have attached to this mail as I am going to reply to that one as
well.
 
Here I am going to change my position because I think choreographies are
different.  Normally (possibly though what is normal may vary and be subject
to debate!!) one might expect a root choreography to drive the complete
choreography description and for the complete evolution to be shown in a
connected manner.  I think this is what you are wanting to restrict CDL to.
I agree it is perhaps the usual case as I have just said, but I do not think
it has to be the only one.  If you add a third choreography as in the
attached XML doc and there is no default lexical ordering rule (my original
point) then we can say that the rules of CDL mean that choreography 1 will
happen first as that is marked as the root, but we can not tell the order of
choreographies 2 and 3.  They may happen on either order, or overlapped /
concurrently.
 
One has to remember that at one level a choreography description is just
marks on paper or bits in a computer.  It is a description of something, not
the thing itself.  So if someone has chosen to put three actually
independent choreographies in a description (perhaps so that one or other
can be cut and pasted / XIncluded into another description I think that is
just fine.  We already have the problem of what makes a particular endpoint
start up a choreography and which choreography description (out of many
potential ones) is it obeying.  This situation adds the different but
similar type of problem of what makes the 2nd and 3rd choreographies start
up and what determines there ordering (concurrency).  In an actual instance
of execution of a choreography description they may be some link that is
hidden i.e. not described in the choreography description, or it may be that
this choreography description is not intended to ever be executed, it is
just a repository of useful choreographies for use elsewhere.
 
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: Gary Brown [mailto:gary@enigmatec.net] 
Sent: 16 March 2005 17:05
To: Tony Fletcher; public-ws-chor@w3.org
Subject: Re: Issue 998 - State that sequential lexically ordering is the
default for interpretation of CDL


Hi Tony
 
I believe a workunit can only have one immediate child activity, so if you
wanted more than one activity, you would need to place them inside a
sequence, parallel or choice anyway.
 
Regards
Gary

----- Original Message ----- 
From: Tony Fletcher <mailto:tony_fletcher@btopenworld.com>  
To: public-ws-chor@w3.org 
Sent: Wednesday, March 16, 2005 2:32 PM
Subject: Issue 998 - State that sequential lexically ordering is the default
for interpretation of CDL

Dear Colleagues,
 
I was hoping to illustrate the point of this issue by taking some of the
examples from the the specification directly, but unfortunately they are all
a bit too simple in that they only have one activity in a series.  The point
I am addressing comes into play when there is more than one activity in
series in the choreography description not wrapped in an explicit SEQUENCE,
PARALLEL or CHOICE construct, which is currently permitted.  So I have just
taken a couple of partially filled out examples to illustrate the point.
 
Are:


<workunit  name="StockCheck" 

           guard="cdl:getVariable('StockQuantity','','"/Product/Qty"', 

                                  '"tns:Retailer") > 10')"            

           block="false" >

   ... <!--some activity -->

   ... <!--some other activity -->

</workunit>

 
and 


<workunit  name="StockCheck" 

           guard="cdl:getVariable('StockQuantity','','"/Product/Qty"', 

                                  '"tns:Retailer") > 10')"            

           block="false" >

   ... <!--some other activity -->

   ... <!--some activity -->

</workunit>




the same?  (Where typically 'some activity' would be an interaction and
'some other activity' would be a different interaction.)

Another pseudo example:



<workunit  name="StockCheck">

   ... <interaction name="1" ...>

   ... <interaction name="2" ...>

</workunit>

workunit  name="StockReplenish">

   ... <interaction name="3" ...>

</workunit>

and



workunit  name="StockReplenish">

   ... <interaction name="3" ...>

</workunit>

<workunit  name="StockCheck">

   ... <interaction name="2" ...>

   ... <interaction name="1" ...>

</workunit>

 

I hope this makes the point clear  One solution is to include a default
ordering statement in the specification as the issue suggests.  Another
solution is to declare all of the above examples illegal CDL and state that
when more than one activity is placed lexically next to another (and they do
not have to be of the same type) then they MUST be wrapped with and explicit
SEQUENCE, PARALLEL or CHOICE activity.

 

 Best Regards,

Tony                           


 <http://www.choreology.com/> 

Tony Fletcher

Technical Advisor 
Choreology Ltd.
68, Lombard Street, London EC3V 9L J   UK


Phone:  

+44 (0) 1473 729537


Mobile: 

+44 (0) 7801 948219


Fax:    

+44 (0) 870 7390077


Web:

 <http://www.choreology.com/> www.choreology.com


CohesionsT


Business transaction management software for application coordination



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