Resilient References? (Re: [ogsa-wg] ogsa London f2f minutes uploaded)

[Andrew Grimshaw]

Frank et. Al.
Let me begin by saying that I believe there are two basic arguments for
keeping resolution out of the base profile and in WS-Naming (really the
WS-Name Resolution component): 1) architectural cleanliness and politics,
and 2) purely technical. Mark Morgan will address (2) in a subsequent email.
I will address (1).

Architectural cleanliness and politics. 
Let's take the architectural issue first. 

What we are taking about is naming and name resolution including rebinding
of existing bindings. Here a binding is some sort of <address, way to
identify the thing the binding is for> tuple. Multi-layer schemes for this
are as old as Moses in distributed systems - and even in regular operating
systems and programming languages (think swizzle).

Now, suppose that we have a mechanism in WSRF-Base Profile for doing the
rebinding as proposed, i.e,  
	ogsa-bp:resilientReference
	ogsa-rns:Resolve

Later, a different OGSA base profile, perhaps for WSI, comes along and they
also need a resolution scheme. So we have another set of names/namespaces
for doing EXACTLY the same thing. 

OR, a basic WS facility, endorsed by many major players, comes along that
also does resolution ... and we yet another way of doing the same thing.

It is, in my opinion, much better to do resolution ONCE, along with other
naming and name resolution, and in such a way as to be completely
INDEPENDENT of grid. Why independent of grid? Because we want a system that
will be as ubiquitous as possible - and used for both "grid services" and
more general "web services".

Now to politics. If we assume for the moment that a) naming and binding has
broader impact than just grids, and b) we are striving for wide-spread
usage, then it is very important that all of the major vendors are willing
to "buy in" to whatever scheme we come up with. The reality right now is
that some vendors will not touch anything associated with WSRF. Yet your
proposal will be in the WSRF-Base-Profile! 

As I mentioned earlier Mark will address some of the more technical issues.
I'll steal some of his thunder and point out that the current proposal in
WS-Naming clearly separates "naming" from "resolution".  Indeed, once could
resolve an EPR that does not contain an abstract name.

Andrew

Ps. Below I comment on some of your specific points, with <AG> .. </AG>
tags.

-----Original Message-----
From: owner-ogsa-wg at ggf.org [mailto:owner-ogsa-wg at ggf.org] On Behalf Of
Frank Siebenlist
Sent: Wednesday, June 01, 2005 8:55 PM
To: ogsa-wg at ggf.org
Cc: Hiro Kishimoto
Subject: Re: Resilient References? (Re: [ogsa-wg] ogsa London f2f minutes
uploaded)

Let me try to argue one more time about NOT including the resilient
reference spec in the ws-naming.

First of all, this resilient reference (RR) is not dependent on any
naming scheme; not on any notion of what an identity is, may be or
smells like: no name is "visible" to the consumer of the RR's EPR as all
is hidden inside of that EPR.

<AG> This is the case in the proposed WS-Naming scheme as well, the consumer
does not have to look at the AbstractName if there is one - and indeed with
the modifications based on Tom's feedback, there need not be an AbstractName
at all. </AG>

The interface has no input message parameter, is extremely simple and
easy to implement - the code that would deal with those RRs would be
fairly straightforward and would provide clients with that extra
stability that will allow them to connect with those resources that may
move, or may listen on other ports, or bound to a different protocol,
whatever...

<AG> Dito </AG>


In other words, it is a thing or rare beauty and an abstraction you
don't find often.

<AG> Dito </AG>

Now the cons of adding this to the ws-naming are:

* all naming discussions that I've been part of get bugged down in
religious discussions about what names are, what identities are, whether
we need them, what their formats are or should be or should not be,
whether we should use URIs or should not, how many naming levels we
need, what interfaces we will have for resolutions and what parameters
will be passed - none of this is trivial and it will take time for all
to agree ... and it is very possible that not all will agree...

<AG> First, as I said above AbstractNames and resolution are separate.
Second, one of the nice things about AbstractNames is they are just strings.
Interpretation is up to the generator of the names, they need no parsing.
</AG>

* ...and the most important thing is that there will also be the notion
of "ws-naming" compliance that is needed for interoperability, which
brings up another complicated discussion of what subset of ws-naming
needs a MUST or a SHOULD...

Note that the RRs are very useful stand-alone, without any of the
additional naming features, bells and whistles.
<AG> See my above comments on cleanliness and politics. </AG>

So in order to keep the RRs save and allow for adoption of RRs, we would
then need a ws-naming "level-0 compliance" that would allow implementers
to adopt the RRs without the rest of ws-naming. Higher level compliances
would then deal with the actual use of names, naming conventions and such.

That last observation could also lead to a decision to split the charter
of ws-naming in two. The first part would deal with RRs only and could
most probably be decided quickly with a separate, very short spec, while
the second part of the charter would deal with the more complicated
matter that involves the visible names. I can imagine that MS would be
very much in favor of such a pragmatic approach.

-Frank.

PS. Please note that I am very interested in ws-naming and truly hope
that useful things will come out of it, but for the reasons stated I
would like to save this little RR-gem from unnecessary delays and
adoption hurdles such that it could actually be deployed.


Frank Siebenlist wrote:

>I've been reading the minutes and was wondering if anything was decided
>about those Resilient References.
>
>Personally I hope it is still in the BP as it seems
>independent/stays-clear of any of the naming issues.
>
>In other words, this seems low hanging fruit and moving it in the naming
>profile could delay adoption (unless anyone can tell me that all the
>naming will be resolved next week ;-) ).
>
>-Frank.
>
>
>
>
>Hiro Kishimoto wrote:
>
>  
>
>>Hi all,
>>
>>Mark and Andreas upload F2F minutes to GridForge.
>>Please have a look and approve them tomorrow.
>>
>> 
>>
>>    
>>
>>>They are now online:
>>>
>>>   
>>>
>>>      
>>>
>>https://forge.gridforum.org/projects/ogsa-wg/document/f2f-minutes-20050524
/en/1
>> 
>>
>>    
>>
>>>   
>>>
>>>      
>>>
>>https://forge.gridforum.org/projects/ogsa-wg/document/f2f-minutes-20050523
/en/1
>>
>>
>>Thanks Mark and Andreas for your excellent minutes!
>>----
>>Hiro Kishimoto
>>
>>
>> 
>>
>>    
>>
>
>  
>

-- 
Frank Siebenlist               franks at mcs.anl.gov
The Globus Alliance - Argonne National Laboratory