RE: [sca-policy] ISSUE POLICY-18 : Should qualifiable intents have adefault qualifier

[Mike Edwards <mike_edwards@uk.ibm.com>]

Dave,

Comments inline.

Yours,  Mike.

Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014    Mobile: +44-7802-467431  
Email:  mike_edwards@uk.ibm.com

David Booz <booz@us.ibm.com> wrote on 27/11/2007
22:24:35:

> Does anyone else think that having two defaults (default quallifiers
AND
> defaults in intent maps) is overly complex?  I think the problems
are more
> fundamental.
> 

It is good to worry about complexity - I'm with you
there.

But what are the "more fundamental" problems?

> I have a different perspective on (1) and (2) from Michael Rowley's
email
> below,
> 
> 1) Any binding should be able to provide an intent without the need
to add
> a policySet.  I see no reason why binding.sca is special in this
regard.
>

But the question for the binding.sca is how does it
handle the case where it
supports a qualified intent, but the service or reference
only specifies
the unqualified form?  Which of the qualified
forms does it use?

I suppose that this could be part of some "configuration"
of binding.sca, but
we have no place for this today.
 
> 2) @mayProvides on bindingType should be used solely to determine
if a
> binding can be attached to a service or reference based on what the
service
> or reference @requires.  It has no bearing on policySet assignment
to the
> service or reference.
> 

Well, it has the bearing that IF the bindingType satisfies
the intent, then
there is no need to search for a policySet to apply
to the binding.

> 3) I think we should decide if we really want to keep intentMaps in
the
> model before we go down these complex cases.  Perhaps we've overly
> complicated the policySet model with intentMaps.  For example
(WS-Policy),
> can we reuse more of the WS-Policy FW feature functions (optional,
> exactlyOne, etc) without needing to put more FW on top of it.

Well, to be fair, going way back when Chris Sharp
was involved with this
effort, we did make some big efforts to use WS-Policy
and WS-Policy attachment
without extensions.

The basic problem is that IF you have some domain
of policy, say such as
confidentiality (encryption), there is no obvious
way within WS-Policy to link 
some intent name (typically a qualifier) to a particular
policy within a policy file.

That was why intent maps were created.

The idea of intents in the first place is to provide
some simple high level
means that a developer or an assembler can indicate
requirements.  There is a
deliberate separation from low level policies since
the low level policies 
may change from installation to installation and may
change with a change of
bindings (say).  Without the indirection provided
by intents, this can't be
done.

Once you have indirection, there has to be some form
of mechanics to resolve
the indirection.  Intent maps are the way in
which this is done currently.
There may be other possible approaches, but without
some mechanism, the whole
idea of intents will not work.

Optional, exactly one, etc don't provide indirection.
 Indeed, I don't think
there is anything within WS-Policy that would provide
this sort of capability.

Unless someone thinks that WS-PolicyAttachment could
be bent to suit our needs.
I have now reached the start of a new path that leads
I know not where - but
there are lots of thorn bushes along the way.  I'll
need some encouragement
before stepping further down there.

> 
> I do realize the implications of what I've written.  When the
design starts
> to get complex we should step back and examine the landscape from
above the
> trees.  Feels like we're patching patches.

Hmm.

> 
> 
> Dave Booz
> STSM, SCA and WebSphere Architecture
> Co-Chair OASIS SCA-Policy TC
> "Distributed objects first, then world hunger"
> Poughkeepsie, NY (845)-435-6093  or  8-295-6093
> e-mail:booz@us.ibm.com
> http://washome.austin.ibm.com/xwiki/bin/view/SCA2Team/WebHome

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