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RE: [w3c sml] Bugzilla Issue: 4639 - Cyclic SML models

From: Wilson, Kirk D <Kirk.Wilson@ca.com>
Date: Wed, 27 Jun 2007 09:50:10 -0400
Message-ID: <F9576E62032243419E097FED5F0E75F30152B9C6@USILMS12.ca.com>
To: "Lynn, James \(Software Escalations\)" <james.lynn@hp.com>, "Valentina Popescu" <popescu@ca.ibm.com>, "Smith, Virginia \(HP Software\)" <virginia.smith@hp.com>
Cc: <public-sml@w3.org>, <public-sml-request@w3.org>
I would urge that an issue that the use cases might try to clarify is
exactly what element the sml:acyclic attribute applies to.  If the
acyclic attribute travels with the sml reference type (be that
sml:refType" or an type defined with sml:ref="true"-however we decide
this issue), then the actual reference elements are children of the
element of the reference type.  Could an element of a sml reference type
have multiple children reference elements, some of which may permit
cylces while others prohibit cycles?  In this case, what is the parent
element of the sml reference type?  I admit, I DON'T have a use case for
this, but I think it is something we need to make sure that we don't
need to consider.


Another question I have is, Is it clear what it means for an instance to
prevent a cycle from occurring in a diagram?  The current text states
that for a type R having acyclic="true", instances of R MUST NOT create
cycles in any model.  If R references S and S is acyclic="false", does a
cycle involving S invalidate the acyclic="true" constraint on R.  I
wouldn't think so, but is that clear from the text.  I believe
"cyclic"/"acyclic" usually apply to graphs as a whole and not to what
individual nodes in the graph are responsible for (I assume that if R
"creates" something, R is "responsible" for that thing).



Kirk Wilson, Ph.D.
Architect, Development

CA Labs / IP&S

603 823-7146



From: public-sml-request@w3.org [mailto:public-sml-request@w3.org] On
Behalf Of Lynn, James (Software Escalations)
Sent: Tuesday, June 26, 2007 9:23 AM
To: Valentina Popescu; Smith, Virginia (HP Software)
Cc: public-sml@w3.org; public-sml-request@w3.org
Subject: RE: Bugzilla Issue: 4639 - Cyclic SML models


I would be in favor of the use case approach. Has anyone out together
use cases for either the element or document cycle cases?



James Lynn 

HP Software 




From: public-sml-request@w3.org [mailto:public-sml-request@w3.org] On
Behalf Of Valentina Popescu
Sent: Tuesday, June 26, 2007 12:36 AM
To: Smith, Virginia (HP Software)
Cc: public-sml@w3.org; public-sml-request@w3.org
Subject: Re: Bugzilla Issue: 4639 - Cyclic SML models

There is an SML validator implementation in the COSMOS open source
project http://www.eclipse.org/cosmos/ <http://www.eclipse.org/cosmos/>
and I am leading this team. 
We did not have any issue with supporting cycles at the element level as
opposed to ( or complementing ) document cycles as described by the
current specification. Our validator is using a file based SML
repository implementation. 

To be honest, I think that what is missing here are the set of usecases
we want to enable with this function. 

Thank you,
Valentina Popescu
IBM Toronto Labs
Phone:  (905)413-2412         (tie-line  969)
Fax: (905) 413-4850

"Smith, Virginia (HP Software)" <virginia.smith@hp.com> 
Sent by: public-sml-request@w3.org 

06/25/2007 05:45 PM 






Bugzilla Issue: 4639 - Cyclic SML models




This email is to start a discussion on document-based cycles vs.
element-based cycles in SML.

In the current SML spec, there is a mismatch in that references are
defined as pointing to elements and model cycles are defined based on
documents. Since the concept is question (references) are based on
elements, it makes sense to me that SML model cycles should be defined
based on elements. 

I see 2 scenarios that pose a problem when testing for cycles according
to the current spec.

1) Since a reference can point to an element defined in the same
document as the reference, a cycle could exist within a single document
but not appear as a cycle in a document-based graph. (false negative)

2) Let's say Document A contains a reference to element X in Document B
and Document B contains a reference to element Y in Document A and
elements X and Y are not related in any way. This is not really a cycle
(of element references) but will appear as a cycle in a document-based
graph. (false positive)

I think we need to answer the following question:

- Are there implementation-related reasons to support document-based
graphs but not element-based graphs? (An SML validator implementation
must be realistically achievable.) 

Does anyone have experience with implementing an SML validator (or know
someone with relevant experience)? 


Virginia Smith 
HP Software / BTO R&D
8000 Foothills Blvd | Roseville | CA 95747
Received on Wednesday, 27 June 2007 13:50:32 UTC

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