Re: Action 218 Subject Attachment Extensibility in guidelines

Umit and Maryann,
We'd suggest some minor editorial comments to this proposed text, and 
consideration if a best practice may also be advised.

See .pdf and .htm attached with redlines.

Thanks.

>Yalcinalp, Umit wrote: The following text completes our action item 218 for Subject Attachment
>Extensibility. It is proposed as a new subsection in Section 5. 
>
>Umit and Maryann
>
>[Action 218] http://www.w3.org/2005/06/tracker/wspolicy/actions/218
>Note: The text will use the reference that is already existing in the
>guidelines document to WS-RM Policy. 
>
>
>-------------------------------------
>5.3 Subject Attachment Extensibility: 
>Overtime, a policy expression may evolve to be applicable to policy
>subjects different than the policy subjects that it was originally
>designed for. When this type of evolution occurs, the author of the
>assertion should carefully consider the applicability of this usage with
>respect to the compatibility of the assertion's semantics. When an
>assertion needs to evolve to indicate a behavior that is no longer
>compatible with its originally intended semantics or policy subjects, a
>new namespace should be designed to designate the new behavior that is
>signified with the new namespace. Section 5.2 further clarifies the
>usage of multiple behaviors. 
>In general, it is NOT recommended to deprecate policy subjects by
>reducing the policy subjects that an assertion was originally designed
>for. 
>When the assertion's semantics does not change to invalidate any of the
>original policy subjects but new policy subjects need to be added, it
>may be possible to use the same assertion to designate the additional
>policy subjects without a namespace change.  The authors must retain the
>compatible behavior of the policy assertion. For example, a policy
>assertion for a protocol that is originally designed for endpoint policy
>subject may add message policy subject to indicate finer granular
>attachment provided that endpoint policy subject is also retained in its
>design. This approach has been used by WS-RM Policy. 
>
>----------------------
>
>Dr. Umit Yalcinalp
>Research Scientist
>SAP Labs, LLC
>Email: umit.yalcinalp@sap.com Tel: (650) 320-3095 
>SDN: https://www.sdn.sap.com/irj/sdn/weblogs?blog=/pub/u/36238
>--------
>"Nearly all men can stand adversity, but if you want to test a man's
>character, give him power." Abraham Lincoln. 
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