Re: Proposal on isolation levels in WS-CDL

The issue I have with the current text, which I believe is also an issue in 
your proposed new text, is that a locking mechanism would be required to 
prevent enclosed choreographies overwriting variables being modified within 
an isolation level of "dirty-read" or "immediately-visible".

The approach used in other parts of the spec may be more appropriate - e.g. 
in assignment, if the activity does not complete successfully, then any 
changes made to variables during that activity will not be made visible - 
however, there is no locking mechanism to prevent concurrent activities from 
also attempting to set the same variables.

Therefore possibly a choreography should also only support two modes - 
changes are either immediately applied or await the successful completion of 
the choreography.

This would avoid any need to support a locking mechanism, and would ensure 
consistency in the way changes are applied (and become visible) across the 
CDL specification.

Regards
Gary

----- Original Message ----- 
From: "Steve Ross-Talbot" <steve@enigmatec.net>
To: "WS-Choreography List" <public-ws-chor@w3.org>
Sent: Tuesday, November 02, 2004 8:13 PM
Subject: Proposal on isolation levels in WS-CDL


>
> Gary,
>
> enclosed is my proposal for isolation levels.
>
> The specification today says:
>
> "The optional isolation attribute specifies when a variable information 
> that is defined in an enclosing and changed within an enclosed 
> Choreography is visible to its enclosing and sibling Choreographies:
>
> · When isolation is set to "dirty-write", the variable information can be 
> immediately overwritten by actions in other Choreographies
>
> · When isolation is set to "dirty-read", the variable information is 
> immediately visible to other Choreographies
>
> When isolation is set to "serializable", the variable information is 
> visible to other Choreographies only after this Choreography has ended 
> successfully"
>
> The first point I want to make is that the text itself is most unclear as 
> to what the visible scope is for a variable given it's isolation level.
> The second point I want to make is that it is unclear as to what the 
> purpose of isolation levels really is.
>
> How can we resolve this? We can do it in one of two ways. The first way is 
> to clarify the text so that the purpose and semantics of the isolation 
> levels is made clearer (Proposal One) and the second (Proposal Two) 
> assumes a particular use of isolation levels which, if accepted, could be 
> simplified into visible scopes.
>
> *** Proposal One ***
> Retain isolation levels but replace the existing text (above) with the 
> following:
>
> "The purpose of the the isolation attribute is to define the visible scope 
> of a variable. That is it describes when changes to
> a variable defined within the enclosing choreography are visible to 
> enclosed choreographies. In this context an enclosing choreography is 
> defined as the out-most defined choreography relative to the enclosed 
> choreography. An enclosing choreography is the one in which the variable 
> is defined. An enclosed choreography is a choreography that is enclosed by 
> the enclosed choreography such that it changes a variable defined in the 
> enclosing choreography. A sibling choreography is an enclosed choreography 
> that has a common outer-choreography that is shared with the other 
> enclosing choreographies such that the variable is not changed but may be 
> accessed.
>
> The optional isolation attribute specifies when a variable information 
> that is defined in an enclosing and changed within an enclosed 
> Choreography is visible to its enclosing and sibling Choreographies:
>
> · When isolation is set to "dirty-write", the variable information can be 
> immediately overwritten by actions in other enclosed choreographies.
>
> · When isolation is set to "dirty-read", the variable information is 
> immediately visible to other enclosed and sibling choroegraphies but 
> cannot be over written.
>
> When isolation is set to "serializable", the variable information is 
> visible to other enclosed and sibiling only after the enclosed 
> choreography changing the variable has ended successfully. If the optional 
> isolation attribute is not present then variable information defined 
> within in either and enclosing, sibling or enclosed choreographies 
> defaults to serializable".
>
>
> *** Proposal Two ***
> Remove isolation levels and add the following scope attribute to variable 
> definitions with the enclosed text:
>
> Replace "isolation" with "visible-scope".
> Replace "dirty-write" with "immediately-available"
> Replace "dirty-read" with "immediately-visible"
> Replace "serializable" with "locally-available"
>
> Replace the modified text above with:
> "The purpose of the the visible-scope attribute is to define the visible 
> scope of a variable. That is it describes when changes to
> a variable defined within the enclosing choreography are visible to 
> enclosed choreographies. In this context an enclosing choreography is 
> defined as the out-most defined choreography relative to the enclosed 
> choreography. An enclosing choreography is the one in which the variable 
> is defined. An enclosed choreography is a choreography that is enclosed by 
> the enclosed choreography such that it changes a variable defined in the 
> enclosing choreography. A sibling choreography is an enclosed choreography 
> that has a common outer-choreography that is shared with the other 
> enclosing choreographies such that the variable is not changed but may be 
> accessed.
>
> The optional visible-scope attribute specifies when a variable information 
> that is defined in an enclosing and changed within an enclosed 
> Choreography is visible to its enclosing and sibling Choreographies:
>
> · When visible-scope is set to "immediately-available", the variable 
> information can be immediately overwritten by actions in other enclosed 
> choreographies.
>
> · When visible-scope is set to "immediately-visible", the variable 
> information is immediately visible to other enclosed and sibling 
> choroegraphies but cannot be over written.
>
> · When visible-scope is set to "locally-available", the variable 
> information is visible to other enclosed and sibiling only after the 
> enclosed choreography changing the variable has ended successfully, hence 
> changes to the variable are "locally available" and not available outside 
> of the choreography that made the changes until that choreography 
> completes successfully.
>
> If the optional visible-scope attribute is not present then variable 
> information defined within in either and enclosing, sibling or enclosed 
> choreographies defaults to "locally-available".
>
>

Received on Thursday, 4 November 2004 12:08:01 UTC